/* * Copyright (c) 2017-present, Facebook, Inc. * All rights reserved. * * This source code is licensed under the BSD-style license found in the * LICENSE file in the root directory of this source tree. An additional grant * of patent rights can be found in the PATENTS file in the same directory. */ /// Zstandard educational decoder implementation /// See https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md #include #include #include #include #include "zstd_decompress.h" /******* UTILITY MACROS AND TYPES *********************************************/ // Max block size decompressed size is 128 KB and literal blocks can't be // larger than their block #define MAX_LITERALS_SIZE ((size_t)128 * 1024) #define MAX(a, b) ((a) > (b) ? (a) : (b)) #define MIN(a, b) ((a) < (b) ? (a) : (b)) /// This decoder calls exit(1) when it encounters an error, however a production /// library should propagate error codes #define ERROR(s) \ do { \ fprintf(stderr, "Error: %s\n", s); \ exit(1); \ } while (0) #define INP_SIZE() \ ERROR("Input buffer smaller than it should be or input is " \ "corrupted") #define OUT_SIZE() ERROR("Output buffer too small for output") #define CORRUPTION() ERROR("Corruption detected while decompressing") #define BAD_ALLOC() ERROR("Memory allocation error") #define IMPOSSIBLE() ERROR("An impossibility has occurred") typedef uint8_t u8; typedef uint16_t u16; typedef uint32_t u32; typedef uint64_t u64; typedef int8_t i8; typedef int16_t i16; typedef int32_t i32; typedef int64_t i64; /******* END UTILITY MACROS AND TYPES *****************************************/ /******* IMPLEMENTATION PRIMITIVE PROTOTYPES **********************************/ /// The implementations for these functions can be found at the bottom of this /// file. They implement low-level functionality needed for the higher level /// decompression functions. /*** IO STREAM OPERATIONS *************/ /// ostream_t/istream_t are used to wrap the pointers/length data passed into /// ZSTD_decompress, so that all IO operations are safely bounds checked /// They are written/read forward, and reads are treated as little-endian /// They should be used opaquely to ensure safety typedef struct { u8 *ptr; size_t len; } ostream_t; typedef struct { const u8 *ptr; size_t len; // Input often reads a few bits at a time, so maintain an internal offset int bit_offset; } istream_t; /// The following two functions are the only ones that allow the istream to be /// non-byte aligned /// Reads `num` bits from a bitstream, and updates the internal offset static inline u64 IO_read_bits(istream_t *const in, const int num_bits); /// Backs-up the stream by `num` bits so they can be read again static inline void IO_rewind_bits(istream_t *const in, const int num_bits); /// If the remaining bits in a byte will be unused, advance to the end of the /// byte static inline void IO_align_stream(istream_t *const in); /// Write the given byte into the output stream static inline void IO_write_byte(ostream_t *const out, u8 symb); /// Returns the number of bytes left to be read in this stream. The stream must /// be byte aligned. static inline size_t IO_istream_len(const istream_t *const in); /// Advances the stream by `len` bytes, and returns a pointer to the chunk that /// was skipped. The stream must be byte aligned. static inline const u8 *IO_read_bytes(istream_t *const in, size_t len); /// Advances the stream by `len` bytes, and returns a pointer to the chunk that /// was skipped so it can be written to. static inline u8 *IO_write_bytes(ostream_t *const out, size_t len); /// Advance the inner state by `len` bytes. The stream must be byte aligned. static inline void IO_advance_input(istream_t *const in, size_t len); /// Returns an `ostream_t` constructed from the given pointer and length. static inline ostream_t IO_make_ostream(u8 *out, size_t len); /// Returns an `istream_t` constructed from the given pointer and length. static inline istream_t IO_make_istream(const u8 *in, size_t len); /// Returns an `istream_t` with the same base as `in`, and length `len`. /// Then, advance `in` to account for the consumed bytes. /// `in` must be byte aligned. static inline istream_t IO_make_sub_istream(istream_t *const in, size_t len); /*** END IO STREAM OPERATIONS *********/ /*** BITSTREAM OPERATIONS *************/ /// Read `num` bits (up to 64) from `src + offset`, where `offset` is in bits, /// and return them interpreted as a little-endian unsigned integer. static inline u64 read_bits_LE(const u8 *src, const int num_bits, const size_t offset); /// Read bits from the end of a HUF or FSE bitstream. `offset` is in bits, so /// it updates `offset` to `offset - bits`, and then reads `bits` bits from /// `src + offset`. If the offset becomes negative, the extra bits at the /// bottom are filled in with `0` bits instead of reading from before `src`. static inline u64 STREAM_read_bits(const u8 *src, const int bits, i64 *const offset); /*** END BITSTREAM OPERATIONS *********/ /*** BIT COUNTING OPERATIONS **********/ /// Returns the index of the highest set bit in `num`, or `-1` if `num == 0` static inline int highest_set_bit(const u64 num); /*** END BIT COUNTING OPERATIONS ******/ /*** HUFFMAN PRIMITIVES ***************/ // Table decode method uses exponential memory, so we need to limit depth #define HUF_MAX_BITS (16) // Limit the maximum number of symbols to 256 so we can store a symbol in a byte #define HUF_MAX_SYMBS (256) /// Structure containing all tables necessary for efficient Huffman decoding typedef struct { u8 *symbols; u8 *num_bits; int max_bits; } HUF_dtable; /// Decode a single symbol and read in enough bits to refresh the state static inline u8 HUF_decode_symbol(const HUF_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset); /// Read in a full state's worth of bits to initialize it static inline void HUF_init_state(const HUF_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset); /// Decompresses a single Huffman stream, returns the number of bytes decoded. /// `src_len` must be the exact length of the Huffman-coded block. static size_t HUF_decompress_1stream(const HUF_dtable *const dtable, ostream_t *const out, istream_t *const in); /// Same as previous but decodes 4 streams, formatted as in the Zstandard /// specification. /// `src_len` must be the exact length of the Huffman-coded block. static size_t HUF_decompress_4stream(const HUF_dtable *const dtable, ostream_t *const out, istream_t *const in); /// Initialize a Huffman decoding table using the table of bit counts provided static void HUF_init_dtable(HUF_dtable *const table, const u8 *const bits, const int num_symbs); /// Initialize a Huffman decoding table using the table of weights provided /// Weights follow the definition provided in the Zstandard specification static void HUF_init_dtable_usingweights(HUF_dtable *const table, const u8 *const weights, const int num_symbs); /// Free the malloc'ed parts of a decoding table static void HUF_free_dtable(HUF_dtable *const dtable); /// Deep copy a decoding table, so that it can be used and free'd without /// impacting the source table. static void HUF_copy_dtable(HUF_dtable *const dst, const HUF_dtable *const src); /*** END HUFFMAN PRIMITIVES ***********/ /*** FSE PRIMITIVES *******************/ /// For more description of FSE see /// https://github.com/Cyan4973/FiniteStateEntropy/ // FSE table decoding uses exponential memory, so limit the maximum accuracy #define FSE_MAX_ACCURACY_LOG (15) // Limit the maximum number of symbols so they can be stored in a single byte #define FSE_MAX_SYMBS (256) /// The tables needed to decode FSE encoded streams typedef struct { u8 *symbols; u8 *num_bits; u16 *new_state_base; int accuracy_log; } FSE_dtable; /// Return the symbol for the current state static inline u8 FSE_peek_symbol(const FSE_dtable *const dtable, const u16 state); /// Read the number of bits necessary to update state, update, and shift offset /// back to reflect the bits read static inline void FSE_update_state(const FSE_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset); /// Combine peek and update: decode a symbol and update the state static inline u8 FSE_decode_symbol(const FSE_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset); /// Read bits from the stream to initialize the state and shift offset back static inline void FSE_init_state(const FSE_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset); /// Decompress two interleaved bitstreams (e.g. compressed Huffman weights) /// using an FSE decoding table. `src_len` must be the exact length of the /// block. static size_t FSE_decompress_interleaved2(const FSE_dtable *const dtable, ostream_t *const out, istream_t *const in); /// Initialize a decoding table using normalized frequencies. static void FSE_init_dtable(FSE_dtable *const dtable, const i16 *const norm_freqs, const int num_symbs, const int accuracy_log); /// Decode an FSE header as defined in the Zstandard format specification and /// use the decoded frequencies to initialize a decoding table. static void FSE_decode_header(FSE_dtable *const dtable, istream_t *const in, const int max_accuracy_log); /// Initialize an FSE table that will always return the same symbol and consume /// 0 bits per symbol, to be used for RLE mode in sequence commands static void FSE_init_dtable_rle(FSE_dtable *const dtable, const u8 symb); /// Free the malloc'ed parts of a decoding table static void FSE_free_dtable(FSE_dtable *const dtable); /// Deep copy a decoding table, so that it can be used and free'd without /// impacting the source table. static void FSE_copy_dtable(FSE_dtable *const dst, const FSE_dtable *const src); /*** END FSE PRIMITIVES ***************/ /******* END IMPLEMENTATION PRIMITIVE PROTOTYPES ******************************/ /******* ZSTD HELPER STRUCTS AND PROTOTYPES ***********************************/ /// A small structure that can be reused in various places that need to access /// frame header information typedef struct { // The size of window that we need to be able to contiguously store for // references size_t window_size; // The total output size of this compressed frame size_t frame_content_size; // The dictionary id if this frame uses one u32 dictionary_id; // Whether or not the content of this frame has a checksum int content_checksum_flag; // Whether or not the output for this frame is in a single segment int single_segment_flag; } frame_header_t; /// The context needed to decode blocks in a frame typedef struct { frame_header_t header; // The total amount of data available for backreferences, to determine if an // offset too large to be correct size_t current_total_output; const u8 *dict_content; size_t dict_content_len; // Entropy encoding tables so they can be repeated by future blocks instead // of retransmitting HUF_dtable literals_dtable; FSE_dtable ll_dtable; FSE_dtable ml_dtable; FSE_dtable of_dtable; // The last 3 offsets for the special "repeat offsets". u64 previous_offsets[3]; } frame_context_t; /// The decoded contents of a dictionary so that it doesn't have to be repeated /// for each frame that uses it struct dictionary_s { // Entropy tables HUF_dtable literals_dtable; FSE_dtable ll_dtable; FSE_dtable ml_dtable; FSE_dtable of_dtable; // Raw content for backreferences u8 *content; size_t content_size; // Offset history to prepopulate the frame's history u64 previous_offsets[3]; u32 dictionary_id; }; /// A tuple containing the parts necessary to decode and execute a ZSTD sequence /// command typedef struct { u32 literal_length; u32 match_length; u32 offset; } sequence_command_t; /// The decoder works top-down, starting at the high level like Zstd frames, and /// working down to lower more technical levels such as blocks, literals, and /// sequences. The high-level functions roughly follow the outline of the /// format specification: /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md /// Before the implementation of each high-level function declared here, the /// prototypes for their helper functions are defined and explained /// Decode a single Zstd frame, or error if the input is not a valid frame. /// Accepts a dict argument, which may be NULL indicating no dictionary. /// See /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frame-concatenation static void decode_frame(ostream_t *const out, istream_t *const in, const dictionary_t *const dict); // Decode data in a compressed block static void decompress_block(frame_context_t *const ctx, ostream_t *const out, istream_t *const in); // Decode the literals section of a block static size_t decode_literals(frame_context_t *const ctx, istream_t *const in, u8 **const literals); // Decode the sequences part of a block static size_t decode_sequences(frame_context_t *const ctx, istream_t *const in, sequence_command_t **const sequences); // Execute the decoded sequences on the literals block static void execute_sequences(frame_context_t *const ctx, ostream_t *const out, const u8 *const literals, const size_t literals_len, const sequence_command_t *const sequences, const size_t num_sequences); /******* END ZSTD HELPER STRUCTS AND PROTOTYPES *******************************/ size_t ZSTD_decompress(void *const dst, const size_t dst_len, const void *const src, const size_t src_len) { dictionary_t* uninit_dict = create_dictionary(); size_t const decomp_size = ZSTD_decompress_with_dict(dst, dst_len, src, src_len, uninit_dict); free_dictionary(uninit_dict); return decomp_size; } size_t ZSTD_decompress_with_dict(void *const dst, const size_t dst_len, const void *const src, const size_t src_len, dictionary_t* parsed_dict) { istream_t in = IO_make_istream(src, src_len); ostream_t out = IO_make_ostream(dst, dst_len); // "A content compressed by Zstandard is transformed into a Zstandard frame. // Multiple frames can be appended into a single file or stream. A frame is // totally independent, has a defined beginning and end, and a set of // parameters which tells the decoder how to decompress it." /* this decoder assumes decompression of a single frame */ decode_frame(&out, &in, parsed_dict); return out.ptr - (u8 *)dst; } /******* FRAME DECODING ******************************************************/ static void decode_data_frame(ostream_t *const out, istream_t *const in, const dictionary_t *const dict); static void init_frame_context(frame_context_t *const context, istream_t *const in, const dictionary_t *const dict); static void free_frame_context(frame_context_t *const context); static void parse_frame_header(frame_header_t *const header, istream_t *const in); static void frame_context_apply_dict(frame_context_t *const ctx, const dictionary_t *const dict); static void decompress_data(frame_context_t *const ctx, ostream_t *const out, istream_t *const in); static void decode_frame(ostream_t *const out, istream_t *const in, const dictionary_t *const dict) { const u32 magic_number = IO_read_bits(in, 32); // Zstandard frame // // "Magic_Number // // 4 Bytes, little-endian format. Value : 0xFD2FB528" if (magic_number == 0xFD2FB528U) { // ZSTD frame decode_data_frame(out, in, dict); return; } // not a real frame or a skippable frame ERROR("Tried to decode non-ZSTD frame"); } /// Decode a frame that contains compressed data. Not all frames do as there /// are skippable frames. /// See /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#general-structure-of-zstandard-frame-format static void decode_data_frame(ostream_t *const out, istream_t *const in, const dictionary_t *const dict) { frame_context_t ctx; // Initialize the context that needs to be carried from block to block init_frame_context(&ctx, in, dict); if (ctx.header.frame_content_size != 0 && ctx.header.frame_content_size > out->len) { OUT_SIZE(); } decompress_data(&ctx, out, in); free_frame_context(&ctx); } /// Takes the information provided in the header and dictionary, and initializes /// the context for this frame static void init_frame_context(frame_context_t *const context, istream_t *const in, const dictionary_t *const dict) { // Most fields in context are correct when initialized to 0 memset(context, 0, sizeof(frame_context_t)); // Parse data from the frame header parse_frame_header(&context->header, in); // Set up the offset history for the repeat offset commands context->previous_offsets[0] = 1; context->previous_offsets[1] = 4; context->previous_offsets[2] = 8; // Apply details from the dict if it exists frame_context_apply_dict(context, dict); } static void free_frame_context(frame_context_t *const context) { HUF_free_dtable(&context->literals_dtable); FSE_free_dtable(&context->ll_dtable); FSE_free_dtable(&context->ml_dtable); FSE_free_dtable(&context->of_dtable); memset(context, 0, sizeof(frame_context_t)); } static void parse_frame_header(frame_header_t *const header, istream_t *const in) { // "The first header's byte is called the Frame_Header_Descriptor. It tells // which other fields are present. Decoding this byte is enough to tell the // size of Frame_Header. // // Bit number Field name // 7-6 Frame_Content_Size_flag // 5 Single_Segment_flag // 4 Unused_bit // 3 Reserved_bit // 2 Content_Checksum_flag // 1-0 Dictionary_ID_flag" const u8 descriptor = IO_read_bits(in, 8); // decode frame header descriptor into flags const u8 frame_content_size_flag = descriptor >> 6; const u8 single_segment_flag = (descriptor >> 5) & 1; const u8 reserved_bit = (descriptor >> 3) & 1; const u8 content_checksum_flag = (descriptor >> 2) & 1; const u8 dictionary_id_flag = descriptor & 3; if (reserved_bit != 0) { CORRUPTION(); } header->single_segment_flag = single_segment_flag; header->content_checksum_flag = content_checksum_flag; // decode window size if (!single_segment_flag) { // "Provides guarantees on maximum back-reference distance that will be // used within compressed data. This information is important for // decoders to allocate enough memory. // // Bit numbers 7-3 2-0 // Field name Exponent Mantissa" u8 window_descriptor = IO_read_bits(in, 8); u8 exponent = window_descriptor >> 3; u8 mantissa = window_descriptor & 7; // Use the algorithm from the specification to compute window size // https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor size_t window_base = (size_t)1 << (10 + exponent); size_t window_add = (window_base / 8) * mantissa; header->window_size = window_base + window_add; } // decode dictionary id if it exists if (dictionary_id_flag) { // "This is a variable size field, which contains the ID of the // dictionary required to properly decode the frame. Note that this // field is optional. When it's not present, it's up to the caller to // make sure it uses the correct dictionary. Format is little-endian." const int bytes_array[] = {0, 1, 2, 4}; const int bytes = bytes_array[dictionary_id_flag]; header->dictionary_id = IO_read_bits(in, bytes * 8); } else { header->dictionary_id = 0; } // decode frame content size if it exists if (single_segment_flag || frame_content_size_flag) { // "This is the original (uncompressed) size. This information is // optional. The Field_Size is provided according to value of // Frame_Content_Size_flag. The Field_Size can be equal to 0 (not // present), 1, 2, 4 or 8 bytes. Format is little-endian." // // if frame_content_size_flag == 0 but single_segment_flag is set, we // still have a 1 byte field const int bytes_array[] = {1, 2, 4, 8}; const int bytes = bytes_array[frame_content_size_flag]; header->frame_content_size = IO_read_bits(in, bytes * 8); if (bytes == 2) { // "When Field_Size is 2, the offset of 256 is added." header->frame_content_size += 256; } } else { header->frame_content_size = 0; } if (single_segment_flag) { // "The Window_Descriptor byte is optional. It is absent when // Single_Segment_flag is set. In this case, the maximum back-reference // distance is the content size itself, which can be any value from 1 to // 2^64-1 bytes (16 EB)." header->window_size = header->frame_content_size; } } /// A dictionary acts as initializing values for the frame context before /// decompression, so we implement it by applying it's predetermined /// tables and content to the context before beginning decompression static void frame_context_apply_dict(frame_context_t *const ctx, const dictionary_t *const dict) { // If the content pointer is NULL then it must be an empty dict if (!dict || !dict->content) return; // If the requested dictionary_id is non-zero, the correct dictionary must // be present if (ctx->header.dictionary_id != 0 && ctx->header.dictionary_id != dict->dictionary_id) { ERROR("Wrong dictionary provided"); } // Copy the dict content to the context for references during sequence // execution ctx->dict_content = dict->content; ctx->dict_content_len = dict->content_size; // If it's a formatted dict copy the precomputed tables in so they can // be used in the table repeat modes if (dict->dictionary_id != 0) { // Deep copy the entropy tables so they can be freed independently of // the dictionary struct HUF_copy_dtable(&ctx->literals_dtable, &dict->literals_dtable); FSE_copy_dtable(&ctx->ll_dtable, &dict->ll_dtable); FSE_copy_dtable(&ctx->of_dtable, &dict->of_dtable); FSE_copy_dtable(&ctx->ml_dtable, &dict->ml_dtable); // Copy the repeated offsets memcpy(ctx->previous_offsets, dict->previous_offsets, sizeof(ctx->previous_offsets)); } } /// Decompress the data from a frame block by block static void decompress_data(frame_context_t *const ctx, ostream_t *const out, istream_t *const in) { // "A frame encapsulates one or multiple blocks. Each block can be // compressed or not, and has a guaranteed maximum content size, which // depends on frame parameters. Unlike frames, each block depends on // previous blocks for proper decoding. However, each block can be // decompressed without waiting for its successor, allowing streaming // operations." int last_block = 0; do { // "Last_Block // // The lowest bit signals if this block is the last one. Frame ends // right after this block. // // Block_Type and Block_Size // // The next 2 bits represent the Block_Type, while the remaining 21 bits // represent the Block_Size. Format is little-endian." last_block = IO_read_bits(in, 1); const int block_type = IO_read_bits(in, 2); const size_t block_len = IO_read_bits(in, 21); switch (block_type) { case 0: { // "Raw_Block - this is an uncompressed block. Block_Size is the // number of bytes to read and copy." const u8 *const read_ptr = IO_read_bytes(in, block_len); u8 *const write_ptr = IO_write_bytes(out, block_len); // Copy the raw data into the output memcpy(write_ptr, read_ptr, block_len); ctx->current_total_output += block_len; break; } case 1: { // "RLE_Block - this is a single byte, repeated N times. In which // case, Block_Size is the size to regenerate, while the // "compressed" block is just 1 byte (the byte to repeat)." const u8 *const read_ptr = IO_read_bytes(in, 1); u8 *const write_ptr = IO_write_bytes(out, block_len); // Copy `block_len` copies of `read_ptr[0]` to the output memset(write_ptr, read_ptr[0], block_len); ctx->current_total_output += block_len; break; } case 2: { // "Compressed_Block - this is a Zstandard compressed block, // detailed in another section of this specification. Block_Size is // the compressed size. // Create a sub-stream for the block istream_t block_stream = IO_make_sub_istream(in, block_len); decompress_block(ctx, out, &block_stream); break; } case 3: // "Reserved - this is not a block. This value cannot be used with // current version of this specification." CORRUPTION(); break; default: IMPOSSIBLE(); } } while (!last_block); if (ctx->header.content_checksum_flag) { // This program does not support checking the checksum, so skip over it // if it's present IO_advance_input(in, 4); } } /******* END FRAME DECODING ***************************************************/ /******* BLOCK DECOMPRESSION **************************************************/ static void decompress_block(frame_context_t *const ctx, ostream_t *const out, istream_t *const in) { // "A compressed block consists of 2 sections : // // Literals_Section // Sequences_Section" // Part 1: decode the literals block u8 *literals = NULL; const size_t literals_size = decode_literals(ctx, in, &literals); // Part 2: decode the sequences block sequence_command_t *sequences = NULL; const size_t num_sequences = decode_sequences(ctx, in, &sequences); // Part 3: combine literals and sequence commands to generate output execute_sequences(ctx, out, literals, literals_size, sequences, num_sequences); free(literals); free(sequences); } /******* END BLOCK DECOMPRESSION **********************************************/ /******* LITERALS DECODING ****************************************************/ static size_t decode_literals_simple(istream_t *const in, u8 **const literals, const int block_type, const int size_format); static size_t decode_literals_compressed(frame_context_t *const ctx, istream_t *const in, u8 **const literals, const int block_type, const int size_format); static void decode_huf_table(HUF_dtable *const dtable, istream_t *const in); static void fse_decode_hufweights(ostream_t *weights, istream_t *const in, int *const num_symbs); static size_t decode_literals(frame_context_t *const ctx, istream_t *const in, u8 **const literals) { // "Literals can be stored uncompressed or compressed using Huffman prefix // codes. When compressed, an optional tree description can be present, // followed by 1 or 4 streams." // // "Literals_Section_Header // // Header is in charge of describing how literals are packed. It's a // byte-aligned variable-size bitfield, ranging from 1 to 5 bytes, using // little-endian convention." // // "Literals_Block_Type // // This field uses 2 lowest bits of first byte, describing 4 different block // types" // // size_format takes between 1 and 2 bits int block_type = IO_read_bits(in, 2); int size_format = IO_read_bits(in, 2); if (block_type <= 1) { // Raw or RLE literals block return decode_literals_simple(in, literals, block_type, size_format); } else { // Huffman compressed literals return decode_literals_compressed(ctx, in, literals, block_type, size_format); } } /// Decodes literals blocks in raw or RLE form static size_t decode_literals_simple(istream_t *const in, u8 **const literals, const int block_type, const int size_format) { size_t size; switch (size_format) { // These cases are in the form ?0 // In this case, the ? bit is actually part of the size field case 0: case 2: // "Size_Format uses 1 bit. Regenerated_Size uses 5 bits (0-31)." IO_rewind_bits(in, 1); size = IO_read_bits(in, 5); break; case 1: // "Size_Format uses 2 bits. Regenerated_Size uses 12 bits (0-4095)." size = IO_read_bits(in, 12); break; case 3: // "Size_Format uses 2 bits. Regenerated_Size uses 20 bits (0-1048575)." size = IO_read_bits(in, 20); break; default: // Size format is in range 0-3 IMPOSSIBLE(); } if (size > MAX_LITERALS_SIZE) { CORRUPTION(); } *literals = malloc(size); if (!*literals) { BAD_ALLOC(); } switch (block_type) { case 0: { // "Raw_Literals_Block - Literals are stored uncompressed." const u8 *const read_ptr = IO_read_bytes(in, size); memcpy(*literals, read_ptr, size); break; } case 1: { // "RLE_Literals_Block - Literals consist of a single byte value repeated N times." const u8 *const read_ptr = IO_read_bytes(in, 1); memset(*literals, read_ptr[0], size); break; } default: IMPOSSIBLE(); } return size; } /// Decodes Huffman compressed literals static size_t decode_literals_compressed(frame_context_t *const ctx, istream_t *const in, u8 **const literals, const int block_type, const int size_format) { size_t regenerated_size, compressed_size; // Only size_format=0 has 1 stream, so default to 4 int num_streams = 4; switch (size_format) { case 0: // "A single stream. Both Compressed_Size and Regenerated_Size use 10 // bits (0-1023)." num_streams = 1; // Fall through as it has the same size format case 1: // "4 streams. Both Compressed_Size and Regenerated_Size use 10 bits // (0-1023)." regenerated_size = IO_read_bits(in, 10); compressed_size = IO_read_bits(in, 10); break; case 2: // "4 streams. Both Compressed_Size and Regenerated_Size use 14 bits // (0-16383)." regenerated_size = IO_read_bits(in, 14); compressed_size = IO_read_bits(in, 14); break; case 3: // "4 streams. Both Compressed_Size and Regenerated_Size use 18 bits // (0-262143)." regenerated_size = IO_read_bits(in, 18); compressed_size = IO_read_bits(in, 18); break; default: // Impossible IMPOSSIBLE(); } if (regenerated_size > MAX_LITERALS_SIZE || compressed_size >= regenerated_size) { CORRUPTION(); } *literals = malloc(regenerated_size); if (!*literals) { BAD_ALLOC(); } ostream_t lit_stream = IO_make_ostream(*literals, regenerated_size); istream_t huf_stream = IO_make_sub_istream(in, compressed_size); if (block_type == 2) { // Decode the provided Huffman table // "This section is only present when Literals_Block_Type type is // Compressed_Literals_Block (2)." HUF_free_dtable(&ctx->literals_dtable); decode_huf_table(&ctx->literals_dtable, &huf_stream); } else { // If the previous Huffman table is being repeated, ensure it exists if (!ctx->literals_dtable.symbols) { CORRUPTION(); } } size_t symbols_decoded; if (num_streams == 1) { symbols_decoded = HUF_decompress_1stream(&ctx->literals_dtable, &lit_stream, &huf_stream); } else { symbols_decoded = HUF_decompress_4stream(&ctx->literals_dtable, &lit_stream, &huf_stream); } if (symbols_decoded != regenerated_size) { CORRUPTION(); } return regenerated_size; } // Decode the Huffman table description static void decode_huf_table(HUF_dtable *const dtable, istream_t *const in) { // "All literal values from zero (included) to last present one (excluded) // are represented by Weight with values from 0 to Max_Number_of_Bits." // "This is a single byte value (0-255), which describes how to decode the list of weights." const u8 header = IO_read_bits(in, 8); u8 weights[HUF_MAX_SYMBS]; memset(weights, 0, sizeof(weights)); int num_symbs; if (header >= 128) { // "This is a direct representation, where each Weight is written // directly as a 4 bits field (0-15). The full representation occupies // ((Number_of_Symbols+1)/2) bytes, meaning it uses a last full byte // even if Number_of_Symbols is odd. Number_of_Symbols = headerByte - // 127" num_symbs = header - 127; const size_t bytes = (num_symbs + 1) / 2; const u8 *const weight_src = IO_read_bytes(in, bytes); for (int i = 0; i < num_symbs; i++) { // "They are encoded forward, 2 // weights to a byte with the first weight taking the top four bits // and the second taking the bottom four (e.g. the following // operations could be used to read the weights: Weight[0] = // (Byte[0] >> 4), Weight[1] = (Byte[0] & 0xf), etc.)." if (i % 2 == 0) { weights[i] = weight_src[i / 2] >> 4; } else { weights[i] = weight_src[i / 2] & 0xf; } } } else { // The weights are FSE encoded, decode them before we can construct the // table istream_t fse_stream = IO_make_sub_istream(in, header); ostream_t weight_stream = IO_make_ostream(weights, HUF_MAX_SYMBS); fse_decode_hufweights(&weight_stream, &fse_stream, &num_symbs); } // Construct the table using the decoded weights HUF_init_dtable_usingweights(dtable, weights, num_symbs); } static void fse_decode_hufweights(ostream_t *weights, istream_t *const in, int *const num_symbs) { const int MAX_ACCURACY_LOG = 7; FSE_dtable dtable; // "An FSE bitstream starts by a header, describing probabilities // distribution. It will create a Decoding Table. For a list of Huffman // weights, maximum accuracy is 7 bits." FSE_decode_header(&dtable, in, MAX_ACCURACY_LOG); // Decode the weights *num_symbs = FSE_decompress_interleaved2(&dtable, weights, in); FSE_free_dtable(&dtable); } /******* END LITERALS DECODING ************************************************/ /******* SEQUENCE DECODING ****************************************************/ /// The combination of FSE states needed to decode sequences typedef struct { FSE_dtable ll_table; FSE_dtable of_table; FSE_dtable ml_table; u16 ll_state; u16 of_state; u16 ml_state; } sequence_states_t; /// Different modes to signal to decode_seq_tables what to do typedef enum { seq_literal_length = 0, seq_offset = 1, seq_match_length = 2, } seq_part_t; typedef enum { seq_predefined = 0, seq_rle = 1, seq_fse = 2, seq_repeat = 3, } seq_mode_t; /// The predefined FSE distribution tables for `seq_predefined` mode static const i16 SEQ_LITERAL_LENGTH_DEFAULT_DIST[36] = { 4, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 1, 1, 1, 1, 1, -1, -1, -1, -1}; static const i16 SEQ_OFFSET_DEFAULT_DIST[29] = { 1, 1, 1, 1, 1, 1, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1}; static const i16 SEQ_MATCH_LENGTH_DEFAULT_DIST[53] = { 1, 4, 3, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, -1, -1, -1, -1, -1, -1, -1}; /// The sequence decoding baseline and number of additional bits to read/add /// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#the-codes-for-literals-lengths-match-lengths-and-offsets static const u32 SEQ_LITERAL_LENGTH_BASELINES[36] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 20, 22, 24, 28, 32, 40, 48, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65538}; static const u8 SEQ_LITERAL_LENGTH_EXTRA_BITS[36] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 4, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}; static const u32 SEQ_MATCH_LENGTH_BASELINES[53] = { 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 37, 39, 41, 43, 47, 51, 59, 67, 83, 99, 131, 259, 515, 1027, 2051, 4099, 8195, 16387, 32771, 65539}; static const u8 SEQ_MATCH_LENGTH_EXTRA_BITS[53] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 4, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}; /// Offset decoding is simpler so we just need a maximum code value static const u8 SEQ_MAX_CODES[3] = {35, -1, 52}; static void decompress_sequences(frame_context_t *const ctx, istream_t *const in, sequence_command_t *const sequences, const size_t num_sequences); static sequence_command_t decode_sequence(sequence_states_t *const state, const u8 *const src, i64 *const offset); static void decode_seq_table(FSE_dtable *const table, istream_t *const in, const seq_part_t type, const seq_mode_t mode); static size_t decode_sequences(frame_context_t *const ctx, istream_t *in, sequence_command_t **const sequences) { // "A compressed block is a succession of sequences . A sequence is a // literal copy command, followed by a match copy command. A literal copy // command specifies a length. It is the number of bytes to be copied (or // extracted) from the literal section. A match copy command specifies an // offset and a length. The offset gives the position to copy from, which // can be within a previous block." size_t num_sequences; // "Number_of_Sequences // // This is a variable size field using between 1 and 3 bytes. Let's call its // first byte byte0." u8 header = IO_read_bits(in, 8); if (header == 0) { // "There are no sequences. The sequence section stops there. // Regenerated content is defined entirely by literals section." *sequences = NULL; return 0; } else if (header < 128) { // "Number_of_Sequences = byte0 . Uses 1 byte." num_sequences = header; } else if (header < 255) { // "Number_of_Sequences = ((byte0-128) << 8) + byte1 . Uses 2 bytes." num_sequences = ((header - 128) << 8) + IO_read_bits(in, 8); } else { // "Number_of_Sequences = byte1 + (byte2<<8) + 0x7F00 . Uses 3 bytes." num_sequences = IO_read_bits(in, 16) + 0x7F00; } *sequences = malloc(num_sequences * sizeof(sequence_command_t)); if (!*sequences) { BAD_ALLOC(); } decompress_sequences(ctx, in, *sequences, num_sequences); return num_sequences; } /// Decompress the FSE encoded sequence commands static void decompress_sequences(frame_context_t *const ctx, istream_t *in, sequence_command_t *const sequences, const size_t num_sequences) { // "The Sequences_Section regroup all symbols required to decode commands. // There are 3 symbol types : literals lengths, offsets and match lengths. // They are encoded together, interleaved, in a single bitstream." // "Symbol compression modes // // This is a single byte, defining the compression mode of each symbol // type." // // Bit number : Field name // 7-6 : Literals_Lengths_Mode // 5-4 : Offsets_Mode // 3-2 : Match_Lengths_Mode // 1-0 : Reserved u8 compression_modes = IO_read_bits(in, 8); if ((compression_modes & 3) != 0) { // Reserved bits set CORRUPTION(); } // "Following the header, up to 3 distribution tables can be described. When // present, they are in this order : // // Literals lengths // Offsets // Match Lengths" // Update the tables we have stored in the context decode_seq_table(&ctx->ll_dtable, in, seq_literal_length, (compression_modes >> 6) & 3); decode_seq_table(&ctx->of_dtable, in, seq_offset, (compression_modes >> 4) & 3); decode_seq_table(&ctx->ml_dtable, in, seq_match_length, (compression_modes >> 2) & 3); sequence_states_t states; // Initialize the decoding tables { states.ll_table = ctx->ll_dtable; states.of_table = ctx->of_dtable; states.ml_table = ctx->ml_dtable; } const size_t len = IO_istream_len(in); const u8 *const src = IO_read_bytes(in, len); // "After writing the last bit containing information, the compressor writes // a single 1-bit and then fills the byte with 0-7 0 bits of padding." const int padding = 8 - highest_set_bit(src[len - 1]); // The offset starts at the end because FSE streams are read backwards i64 bit_offset = len * 8 - padding; // "The bitstream starts with initial state values, each using the required // number of bits in their respective accuracy, decoded previously from // their normalized distribution. // // It starts by Literals_Length_State, followed by Offset_State, and finally // Match_Length_State." FSE_init_state(&states.ll_table, &states.ll_state, src, &bit_offset); FSE_init_state(&states.of_table, &states.of_state, src, &bit_offset); FSE_init_state(&states.ml_table, &states.ml_state, src, &bit_offset); for (size_t i = 0; i < num_sequences; i++) { // Decode sequences one by one sequences[i] = decode_sequence(&states, src, &bit_offset); } if (bit_offset != 0) { CORRUPTION(); } } // Decode a single sequence and update the state static sequence_command_t decode_sequence(sequence_states_t *const states, const u8 *const src, i64 *const offset) { // "Each symbol is a code in its own context, which specifies Baseline and // Number_of_Bits to add. Codes are FSE compressed, and interleaved with raw // additional bits in the same bitstream." // Decode symbols, but don't update states const u8 of_code = FSE_peek_symbol(&states->of_table, states->of_state); const u8 ll_code = FSE_peek_symbol(&states->ll_table, states->ll_state); const u8 ml_code = FSE_peek_symbol(&states->ml_table, states->ml_state); // Offset doesn't need a max value as it's not decoded using a table if (ll_code > SEQ_MAX_CODES[seq_literal_length] || ml_code > SEQ_MAX_CODES[seq_match_length]) { CORRUPTION(); } // Read the interleaved bits sequence_command_t seq; // "Decoding starts by reading the Number_of_Bits required to decode Offset. // It then does the same for Match_Length, and then for Literals_Length." seq.offset = ((u32)1 << of_code) + STREAM_read_bits(src, of_code, offset); seq.match_length = SEQ_MATCH_LENGTH_BASELINES[ml_code] + STREAM_read_bits(src, SEQ_MATCH_LENGTH_EXTRA_BITS[ml_code], offset); seq.literal_length = SEQ_LITERAL_LENGTH_BASELINES[ll_code] + STREAM_read_bits(src, SEQ_LITERAL_LENGTH_EXTRA_BITS[ll_code], offset); // "If it is not the last sequence in the block, the next operation is to // update states. Using the rules pre-calculated in the decoding tables, // Literals_Length_State is updated, followed by Match_Length_State, and // then Offset_State." // If the stream is complete don't read bits to update state if (*offset != 0) { FSE_update_state(&states->ll_table, &states->ll_state, src, offset); FSE_update_state(&states->ml_table, &states->ml_state, src, offset); FSE_update_state(&states->of_table, &states->of_state, src, offset); } return seq; } /// Given a sequence part and table mode, decode the FSE distribution /// Errors if the mode is `seq_repeat` without a pre-existing table in `table` static void decode_seq_table(FSE_dtable *const table, istream_t *const in, const seq_part_t type, const seq_mode_t mode) { // Constant arrays indexed by seq_part_t const i16 *const default_distributions[] = {SEQ_LITERAL_LENGTH_DEFAULT_DIST, SEQ_OFFSET_DEFAULT_DIST, SEQ_MATCH_LENGTH_DEFAULT_DIST}; const size_t default_distribution_lengths[] = {36, 29, 53}; const size_t default_distribution_accuracies[] = {6, 5, 6}; const size_t max_accuracies[] = {9, 8, 9}; if (mode != seq_repeat) { // Free old one before overwriting FSE_free_dtable(table); } switch (mode) { case seq_predefined: { // "Predefined_Mode : uses a predefined distribution table." const i16 *distribution = default_distributions[type]; const size_t symbs = default_distribution_lengths[type]; const size_t accuracy_log = default_distribution_accuracies[type]; FSE_init_dtable(table, distribution, symbs, accuracy_log); break; } case seq_rle: { // "RLE_Mode : it's a single code, repeated Number_of_Sequences times." const u8 symb = IO_read_bytes(in, 1)[0]; FSE_init_dtable_rle(table, symb); break; } case seq_fse: { // "FSE_Compressed_Mode : standard FSE compression. A distribution table // will be present " FSE_decode_header(table, in, max_accuracies[type]); break; } case seq_repeat: // "Repeat_Mode : re-use distribution table from previous compressed // block." // Nothing to do here, table will be unchanged if (!table->symbols) { // This mode is invalid if we don't already have a table CORRUPTION(); } break; default: // Impossible, as mode is from 0-3 IMPOSSIBLE(); break; } } /******* END SEQUENCE DECODING ************************************************/ /******* SEQUENCE EXECUTION ***************************************************/ static void execute_sequences(frame_context_t *const ctx, ostream_t *const out, const u8 *const literals, const size_t literals_len, const sequence_command_t *const sequences, const size_t num_sequences) { istream_t litstream = IO_make_istream(literals, literals_len); u64 *const offset_hist = ctx->previous_offsets; size_t total_output = ctx->current_total_output; for (size_t i = 0; i < num_sequences; i++) { const sequence_command_t seq = sequences[i]; { // If the sequence asks for more literals than are left, the // sequence must be corrupted if (seq.literal_length > IO_istream_len(&litstream)) { CORRUPTION(); } u8 *const write_ptr = IO_write_bytes(out, seq.literal_length); const u8 *const read_ptr = IO_read_bytes(&litstream, seq.literal_length); // Copy literals to output memcpy(write_ptr, read_ptr, seq.literal_length); total_output += seq.literal_length; } size_t offset; // Offsets are special, we need to handle the repeat offsets if (seq.offset <= 3) { // "The first 3 values define a repeated offset and we will call // them Repeated_Offset1, Repeated_Offset2, and Repeated_Offset3. // They are sorted in recency order, with Repeated_Offset1 meaning // 'most recent one'". // Use 0 indexing for the array u32 idx = seq.offset - 1; if (seq.literal_length == 0) { // "There is an exception though, when current sequence's // literals length is 0. In this case, repeated offsets are // shifted by one, so Repeated_Offset1 becomes Repeated_Offset2, // Repeated_Offset2 becomes Repeated_Offset3, and // Repeated_Offset3 becomes Repeated_Offset1 - 1_byte." idx++; } if (idx == 0) { offset = offset_hist[0]; } else { // If idx == 3 then literal length was 0 and the offset was 3, // as per the exception listed above offset = idx < 3 ? offset_hist[idx] : offset_hist[0] - 1; // If idx == 1 we don't need to modify offset_hist[2], since // we're using the second-most recent code if (idx > 1) { offset_hist[2] = offset_hist[1]; } offset_hist[1] = offset_hist[0]; offset_hist[0] = offset; } } else { // When it's not a repeat offset: // "if (Offset_Value > 3) offset = Offset_Value - 3;" offset = seq.offset - 3; // Shift back history offset_hist[2] = offset_hist[1]; offset_hist[1] = offset_hist[0]; offset_hist[0] = offset; } size_t match_length = seq.match_length; u8 *write_ptr = IO_write_bytes(out, match_length); if (total_output <= ctx->header.window_size) { // In this case offset might go back into the dictionary if (offset > total_output + ctx->dict_content_len) { // The offset goes beyond even the dictionary CORRUPTION(); } if (offset > total_output) { // "The rest of the dictionary is its content. The content act // as a "past" in front of data to compress or decompress, so it // can be referenced in sequence commands." const size_t dict_copy = MIN(offset - total_output, match_length); const size_t dict_offset = ctx->dict_content_len - (offset - total_output); memcpy(write_ptr, ctx->dict_content + dict_offset, dict_copy); write_ptr += dict_copy; match_length -= dict_copy; } } else if (offset > ctx->header.window_size) { CORRUPTION(); } // We must copy byte by byte because the match length might be larger // than the offset // ex: if the output so far was "abc", a command with offset=3 and // match_length=6 would produce "abcabcabc" as the new output for (size_t j = 0; j < match_length; j++) { *write_ptr = *(write_ptr - offset); write_ptr++; } total_output += seq.match_length; } // Copy any leftover literals { size_t len = IO_istream_len(&litstream); u8 *const write_ptr = IO_write_bytes(out, len); const u8 *const read_ptr = IO_read_bytes(&litstream, len); memcpy(write_ptr, read_ptr, len); total_output += len; } ctx->current_total_output = total_output; } /******* END SEQUENCE EXECUTION ***********************************************/ /******* OUTPUT SIZE COUNTING *************************************************/ /// Get the decompressed size of an input stream so memory can be allocated in /// advance. /// This implementation assumes `src` points to a single ZSTD-compressed frame size_t ZSTD_get_decompressed_size(const void *src, const size_t src_len) { istream_t in = IO_make_istream(src, src_len); // get decompressed size from ZSTD frame header { const u32 magic_number = IO_read_bits(&in, 32); if (magic_number == 0xFD2FB528U) { // ZSTD frame frame_header_t header; parse_frame_header(&header, &in); if (header.frame_content_size == 0 && !header.single_segment_flag) { // Content size not provided, we can't tell return -1; } return header.frame_content_size; } else { // not a real frame or skippable frame ERROR("ZSTD frame magic number did not match"); } } } /******* END OUTPUT SIZE COUNTING *********************************************/ /******* DICTIONARY PARSING ***************************************************/ #define DICT_SIZE_ERROR() ERROR("Dictionary size cannot be less than 8 bytes") #define NULL_SRC() ERROR("Tried to create dictionary with pointer to null src"); dictionary_t* create_dictionary() { dictionary_t* dict = calloc(1, sizeof(dictionary_t)); if (!dict) { BAD_ALLOC(); } return dict; } static void init_dictionary_content(dictionary_t *const dict, istream_t *const in); void parse_dictionary(dictionary_t *const dict, const void *src, size_t src_len) { const u8 *byte_src = (const u8 *)src; memset(dict, 0, sizeof(dictionary_t)); if (src == NULL) { /* cannot initialize dictionary with null src */ NULL_SRC(); } if (src_len < 8) { DICT_SIZE_ERROR(); } istream_t in = IO_make_istream(byte_src, src_len); const u32 magic_number = IO_read_bits(&in, 32); if (magic_number != 0xEC30A437) { // raw content dict IO_rewind_bits(&in, 32); init_dictionary_content(dict, &in); return; } dict->dictionary_id = IO_read_bits(&in, 32); // "Entropy_Tables : following the same format as the tables in compressed // blocks. They are stored in following order : Huffman tables for literals, // FSE table for offsets, FSE table for match lengths, and FSE table for // literals lengths. It's finally followed by 3 offset values, populating // recent offsets (instead of using {1,4,8}), stored in order, 4-bytes // little-endian each, for a total of 12 bytes. Each recent offset must have // a value < dictionary size." decode_huf_table(&dict->literals_dtable, &in); decode_seq_table(&dict->of_dtable, &in, seq_offset, seq_fse); decode_seq_table(&dict->ml_dtable, &in, seq_match_length, seq_fse); decode_seq_table(&dict->ll_dtable, &in, seq_literal_length, seq_fse); // Read in the previous offset history dict->previous_offsets[0] = IO_read_bits(&in, 32); dict->previous_offsets[1] = IO_read_bits(&in, 32); dict->previous_offsets[2] = IO_read_bits(&in, 32); // Ensure the provided offsets aren't too large // "Each recent offset must have a value < dictionary size." for (int i = 0; i < 3; i++) { if (dict->previous_offsets[i] > src_len) { ERROR("Dictionary corrupted"); } } // "Content : The rest of the dictionary is its content. The content act as // a "past" in front of data to compress or decompress, so it can be // referenced in sequence commands." init_dictionary_content(dict, &in); } static void init_dictionary_content(dictionary_t *const dict, istream_t *const in) { // Copy in the content dict->content_size = IO_istream_len(in); dict->content = malloc(dict->content_size); if (!dict->content) { BAD_ALLOC(); } const u8 *const content = IO_read_bytes(in, dict->content_size); memcpy(dict->content, content, dict->content_size); } /// Free an allocated dictionary void free_dictionary(dictionary_t *const dict) { HUF_free_dtable(&dict->literals_dtable); FSE_free_dtable(&dict->ll_dtable); FSE_free_dtable(&dict->of_dtable); FSE_free_dtable(&dict->ml_dtable); free(dict->content); memset(dict, 0, sizeof(dictionary_t)); } /******* END DICTIONARY PARSING ***********************************************/ /******* IO STREAM OPERATIONS *************************************************/ #define UNALIGNED() ERROR("Attempting to operate on a non-byte aligned stream") /// Reads `num` bits from a bitstream, and updates the internal offset static inline u64 IO_read_bits(istream_t *const in, const int num_bits) { if (num_bits > 64 || num_bits <= 0) { ERROR("Attempt to read an invalid number of bits"); } const size_t bytes = (num_bits + in->bit_offset + 7) / 8; const size_t full_bytes = (num_bits + in->bit_offset) / 8; if (bytes > in->len) { INP_SIZE(); } const u64 result = read_bits_LE(in->ptr, num_bits, in->bit_offset); in->bit_offset = (num_bits + in->bit_offset) % 8; in->ptr += full_bytes; in->len -= full_bytes; return result; } /// If a non-zero number of bits have been read from the current byte, advance /// the offset to the next byte static inline void IO_rewind_bits(istream_t *const in, int num_bits) { if (num_bits < 0) { ERROR("Attempting to rewind stream by a negative number of bits"); } // move the offset back by `num_bits` bits const int new_offset = in->bit_offset - num_bits; // determine the number of whole bytes we have to rewind, rounding up to an // integer number (e.g. if `new_offset == -5`, `bytes == 1`) const i64 bytes = -(new_offset - 7) / 8; in->ptr -= bytes; in->len += bytes; // make sure the resulting `bit_offset` is positive, as mod in C does not // convert numbers from negative to positive (e.g. -22 % 8 == -6) in->bit_offset = ((new_offset % 8) + 8) % 8; } /// If the remaining bits in a byte will be unused, advance to the end of the /// byte static inline void IO_align_stream(istream_t *const in) { if (in->bit_offset != 0) { if (in->len == 0) { INP_SIZE(); } in->ptr++; in->len--; in->bit_offset = 0; } } /// Write the given byte into the output stream static inline void IO_write_byte(ostream_t *const out, u8 symb) { if (out->len == 0) { OUT_SIZE(); } out->ptr[0] = symb; out->ptr++; out->len--; } /// Returns the number of bytes left to be read in this stream. The stream must /// be byte aligned. static inline size_t IO_istream_len(const istream_t *const in) { return in->len; } /// Returns a pointer where `len` bytes can be read, and advances the internal /// state. The stream must be byte aligned. static inline const u8 *IO_read_bytes(istream_t *const in, size_t len) { if (len > in->len) { INP_SIZE(); } if (in->bit_offset != 0) { UNALIGNED(); } const u8 *const ptr = in->ptr; in->ptr += len; in->len -= len; return ptr; } /// Returns a pointer to write `len` bytes to, and advances the internal state static inline u8 *IO_write_bytes(ostream_t *const out, size_t len) { if (len > out->len) { OUT_SIZE(); } u8 *const ptr = out->ptr; out->ptr += len; out->len -= len; return ptr; } /// Advance the inner state by `len` bytes static inline void IO_advance_input(istream_t *const in, size_t len) { if (len > in->len) { INP_SIZE(); } if (in->bit_offset != 0) { UNALIGNED(); } in->ptr += len; in->len -= len; } /// Returns an `ostream_t` constructed from the given pointer and length static inline ostream_t IO_make_ostream(u8 *out, size_t len) { return (ostream_t) { out, len }; } /// Returns an `istream_t` constructed from the given pointer and length static inline istream_t IO_make_istream(const u8 *in, size_t len) { return (istream_t) { in, len, 0 }; } /// Returns an `istream_t` with the same base as `in`, and length `len` /// Then, advance `in` to account for the consumed bytes /// `in` must be byte aligned static inline istream_t IO_make_sub_istream(istream_t *const in, size_t len) { // Consume `len` bytes of the parent stream const u8 *const ptr = IO_read_bytes(in, len); // Make a substream using the pointer to those `len` bytes return IO_make_istream(ptr, len); } /******* END IO STREAM OPERATIONS *********************************************/ /******* BITSTREAM OPERATIONS *************************************************/ /// Read `num` bits (up to 64) from `src + offset`, where `offset` is in bits static inline u64 read_bits_LE(const u8 *src, const int num_bits, const size_t offset) { if (num_bits > 64) { ERROR("Attempt to read an invalid number of bits"); } // Skip over bytes that aren't in range src += offset / 8; size_t bit_offset = offset % 8; u64 res = 0; int shift = 0; int left = num_bits; while (left > 0) { u64 mask = left >= 8 ? 0xff : (((u64)1 << left) - 1); // Read the next byte, shift it to account for the offset, and then mask // out the top part if we don't need all the bits res += (((u64)*src++ >> bit_offset) & mask) << shift; shift += 8 - bit_offset; left -= 8 - bit_offset; bit_offset = 0; } return res; } /// Read bits from the end of a HUF or FSE bitstream. `offset` is in bits, so /// it updates `offset` to `offset - bits`, and then reads `bits` bits from /// `src + offset`. If the offset becomes negative, the extra bits at the /// bottom are filled in with `0` bits instead of reading from before `src`. static inline u64 STREAM_read_bits(const u8 *const src, const int bits, i64 *const offset) { *offset = *offset - bits; size_t actual_off = *offset; size_t actual_bits = bits; // Don't actually read bits from before the start of src, so if `*offset < // 0` fix actual_off and actual_bits to reflect the quantity to read if (*offset < 0) { actual_bits += *offset; actual_off = 0; } u64 res = read_bits_LE(src, actual_bits, actual_off); if (*offset < 0) { // Fill in the bottom "overflowed" bits with 0's res = -*offset >= 64 ? 0 : (res << -*offset); } return res; } /******* END BITSTREAM OPERATIONS *********************************************/ /******* BIT COUNTING OPERATIONS **********************************************/ /// Returns `x`, where `2^x` is the largest power of 2 less than or equal to /// `num`, or `-1` if `num == 0`. static inline int highest_set_bit(const u64 num) { for (int i = 63; i >= 0; i--) { if (((u64)1 << i) <= num) { return i; } } return -1; } /******* END BIT COUNTING OPERATIONS ******************************************/ /******* HUFFMAN PRIMITIVES ***************************************************/ static inline u8 HUF_decode_symbol(const HUF_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset) { // Look up the symbol and number of bits to read const u8 symb = dtable->symbols[*state]; const u8 bits = dtable->num_bits[*state]; const u16 rest = STREAM_read_bits(src, bits, offset); // Shift `bits` bits out of the state, keeping the low order bits that // weren't necessary to determine this symbol. Then add in the new bits // read from the stream. *state = ((*state << bits) + rest) & (((u16)1 << dtable->max_bits) - 1); return symb; } static inline void HUF_init_state(const HUF_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset) { // Read in a full `dtable->max_bits` bits to initialize the state const u8 bits = dtable->max_bits; *state = STREAM_read_bits(src, bits, offset); } static size_t HUF_decompress_1stream(const HUF_dtable *const dtable, ostream_t *const out, istream_t *const in) { const size_t len = IO_istream_len(in); if (len == 0) { INP_SIZE(); } const u8 *const src = IO_read_bytes(in, len); // "Each bitstream must be read backward, that is starting from the end down // to the beginning. Therefore it's necessary to know the size of each // bitstream. // // It's also necessary to know exactly which bit is the latest. This is // detected by a final bit flag : the highest bit of latest byte is a // final-bit-flag. Consequently, a last byte of 0 is not possible. And the // final-bit-flag itself is not part of the useful bitstream. Hence, the // last byte contains between 0 and 7 useful bits." const int padding = 8 - highest_set_bit(src[len - 1]); // Offset starts at the end because HUF streams are read backwards i64 bit_offset = len * 8 - padding; u16 state; HUF_init_state(dtable, &state, src, &bit_offset); size_t symbols_written = 0; while (bit_offset > -dtable->max_bits) { // Iterate over the stream, decoding one symbol at a time IO_write_byte(out, HUF_decode_symbol(dtable, &state, src, &bit_offset)); symbols_written++; } // "The process continues up to reading the required number of symbols per // stream. If a bitstream is not entirely and exactly consumed, hence // reaching exactly its beginning position with all bits consumed, the // decoding process is considered faulty." // When all symbols have been decoded, the final state value shouldn't have // any data from the stream, so it should have "read" dtable->max_bits from // before the start of `src` // Therefore `offset`, the edge to start reading new bits at, should be // dtable->max_bits before the start of the stream if (bit_offset != -dtable->max_bits) { CORRUPTION(); } return symbols_written; } static size_t HUF_decompress_4stream(const HUF_dtable *const dtable, ostream_t *const out, istream_t *const in) { // "Compressed size is provided explicitly : in the 4-streams variant, // bitstreams are preceded by 3 unsigned little-endian 16-bits values. Each // value represents the compressed size of one stream, in order. The last // stream size is deducted from total compressed size and from previously // decoded stream sizes" const size_t csize1 = IO_read_bits(in, 16); const size_t csize2 = IO_read_bits(in, 16); const size_t csize3 = IO_read_bits(in, 16); istream_t in1 = IO_make_sub_istream(in, csize1); istream_t in2 = IO_make_sub_istream(in, csize2); istream_t in3 = IO_make_sub_istream(in, csize3); istream_t in4 = IO_make_sub_istream(in, IO_istream_len(in)); size_t total_output = 0; // Decode each stream independently for simplicity // If we wanted to we could decode all 4 at the same time for speed, // utilizing more execution units total_output += HUF_decompress_1stream(dtable, out, &in1); total_output += HUF_decompress_1stream(dtable, out, &in2); total_output += HUF_decompress_1stream(dtable, out, &in3); total_output += HUF_decompress_1stream(dtable, out, &in4); return total_output; } /// Initializes a Huffman table using canonical Huffman codes /// For more explanation on canonical Huffman codes see /// http://www.cs.uofs.edu/~mccloske/courses/cmps340/huff_canonical_dec2015.html /// Codes within a level are allocated in symbol order (i.e. smaller symbols get /// earlier codes) static void HUF_init_dtable(HUF_dtable *const table, const u8 *const bits, const int num_symbs) { memset(table, 0, sizeof(HUF_dtable)); if (num_symbs > HUF_MAX_SYMBS) { ERROR("Too many symbols for Huffman"); } u8 max_bits = 0; u16 rank_count[HUF_MAX_BITS + 1]; memset(rank_count, 0, sizeof(rank_count)); // Count the number of symbols for each number of bits, and determine the // depth of the tree for (int i = 0; i < num_symbs; i++) { if (bits[i] > HUF_MAX_BITS) { ERROR("Huffman table depth too large"); } max_bits = MAX(max_bits, bits[i]); rank_count[bits[i]]++; } const size_t table_size = 1 << max_bits; table->max_bits = max_bits; table->symbols = malloc(table_size); table->num_bits = malloc(table_size); if (!table->symbols || !table->num_bits) { free(table->symbols); free(table->num_bits); BAD_ALLOC(); } // "Symbols are sorted by Weight. Within same Weight, symbols keep natural // order. Symbols with a Weight of zero are removed. Then, starting from // lowest weight, prefix codes are distributed in order." u32 rank_idx[HUF_MAX_BITS + 1]; // Initialize the starting codes for each rank (number of bits) rank_idx[max_bits] = 0; for (int i = max_bits; i >= 1; i--) { rank_idx[i - 1] = rank_idx[i] + rank_count[i] * (1 << (max_bits - i)); // The entire range takes the same number of bits so we can memset it memset(&table->num_bits[rank_idx[i]], i, rank_idx[i - 1] - rank_idx[i]); } if (rank_idx[0] != table_size) { CORRUPTION(); } // Allocate codes and fill in the table for (int i = 0; i < num_symbs; i++) { if (bits[i] != 0) { // Allocate a code for this symbol and set its range in the table const u16 code = rank_idx[bits[i]]; // Since the code doesn't care about the bottom `max_bits - bits[i]` // bits of state, it gets a range that spans all possible values of // the lower bits const u16 len = 1 << (max_bits - bits[i]); memset(&table->symbols[code], i, len); rank_idx[bits[i]] += len; } } } static void HUF_init_dtable_usingweights(HUF_dtable *const table, const u8 *const weights, const int num_symbs) { // +1 because the last weight is not transmitted in the header if (num_symbs + 1 > HUF_MAX_SYMBS) { ERROR("Too many symbols for Huffman"); } u8 bits[HUF_MAX_SYMBS]; u64 weight_sum = 0; for (int i = 0; i < num_symbs; i++) { // Weights are in the same range as bit count if (weights[i] > HUF_MAX_BITS) { CORRUPTION(); } weight_sum += weights[i] > 0 ? (u64)1 << (weights[i] - 1) : 0; } // Find the first power of 2 larger than the sum const int max_bits = highest_set_bit(weight_sum) + 1; const u64 left_over = ((u64)1 << max_bits) - weight_sum; // If the left over isn't a power of 2, the weights are invalid if (left_over & (left_over - 1)) { CORRUPTION(); } // left_over is used to find the last weight as it's not transmitted // by inverting 2^(weight - 1) we can determine the value of last_weight const int last_weight = highest_set_bit(left_over) + 1; for (int i = 0; i < num_symbs; i++) { // "Number_of_Bits = Number_of_Bits ? Max_Number_of_Bits + 1 - Weight : 0" bits[i] = weights[i] > 0 ? (max_bits + 1 - weights[i]) : 0; } bits[num_symbs] = max_bits + 1 - last_weight; // Last weight is always non-zero HUF_init_dtable(table, bits, num_symbs + 1); } static void HUF_free_dtable(HUF_dtable *const dtable) { free(dtable->symbols); free(dtable->num_bits); memset(dtable, 0, sizeof(HUF_dtable)); } static void HUF_copy_dtable(HUF_dtable *const dst, const HUF_dtable *const src) { if (src->max_bits == 0) { memset(dst, 0, sizeof(HUF_dtable)); return; } const size_t size = (size_t)1 << src->max_bits; dst->max_bits = src->max_bits; dst->symbols = malloc(size); dst->num_bits = malloc(size); if (!dst->symbols || !dst->num_bits) { BAD_ALLOC(); } memcpy(dst->symbols, src->symbols, size); memcpy(dst->num_bits, src->num_bits, size); } /******* END HUFFMAN PRIMITIVES ***********************************************/ /******* FSE PRIMITIVES *******************************************************/ /// For more description of FSE see /// https://github.com/Cyan4973/FiniteStateEntropy/ /// Allow a symbol to be decoded without updating state static inline u8 FSE_peek_symbol(const FSE_dtable *const dtable, const u16 state) { return dtable->symbols[state]; } /// Consumes bits from the input and uses the current state to determine the /// next state static inline void FSE_update_state(const FSE_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset) { const u8 bits = dtable->num_bits[*state]; const u16 rest = STREAM_read_bits(src, bits, offset); *state = dtable->new_state_base[*state] + rest; } /// Decodes a single FSE symbol and updates the offset static inline u8 FSE_decode_symbol(const FSE_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset) { const u8 symb = FSE_peek_symbol(dtable, *state); FSE_update_state(dtable, state, src, offset); return symb; } static inline void FSE_init_state(const FSE_dtable *const dtable, u16 *const state, const u8 *const src, i64 *const offset) { // Read in a full `accuracy_log` bits to initialize the state const u8 bits = dtable->accuracy_log; *state = STREAM_read_bits(src, bits, offset); } static size_t FSE_decompress_interleaved2(const FSE_dtable *const dtable, ostream_t *const out, istream_t *const in) { const size_t len = IO_istream_len(in); if (len == 0) { INP_SIZE(); } const u8 *const src = IO_read_bytes(in, len); // "Each bitstream must be read backward, that is starting from the end down // to the beginning. Therefore it's necessary to know the size of each // bitstream. // // It's also necessary to know exactly which bit is the latest. This is // detected by a final bit flag : the highest bit of latest byte is a // final-bit-flag. Consequently, a last byte of 0 is not possible. And the // final-bit-flag itself is not part of the useful bitstream. Hence, the // last byte contains between 0 and 7 useful bits." const int padding = 8 - highest_set_bit(src[len - 1]); i64 offset = len * 8 - padding; u16 state1, state2; // "The first state (State1) encodes the even indexed symbols, and the // second (State2) encodes the odd indexes. State1 is initialized first, and // then State2, and they take turns decoding a single symbol and updating // their state." FSE_init_state(dtable, &state1, src, &offset); FSE_init_state(dtable, &state2, src, &offset); // Decode until we overflow the stream // Since we decode in reverse order, overflowing the stream is offset going // negative size_t symbols_written = 0; while (1) { // "The number of symbols to decode is determined by tracking bitStream // overflow condition: If updating state after decoding a symbol would // require more bits than remain in the stream, it is assumed the extra // bits are 0. Then, the symbols for each of the final states are // decoded and the process is complete." IO_write_byte(out, FSE_decode_symbol(dtable, &state1, src, &offset)); symbols_written++; if (offset < 0) { // There's still a symbol to decode in state2 IO_write_byte(out, FSE_peek_symbol(dtable, state2)); symbols_written++; break; } IO_write_byte(out, FSE_decode_symbol(dtable, &state2, src, &offset)); symbols_written++; if (offset < 0) { // There's still a symbol to decode in state1 IO_write_byte(out, FSE_peek_symbol(dtable, state1)); symbols_written++; break; } } return symbols_written; } static void FSE_init_dtable(FSE_dtable *const dtable, const i16 *const norm_freqs, const int num_symbs, const int accuracy_log) { if (accuracy_log > FSE_MAX_ACCURACY_LOG) { ERROR("FSE accuracy too large"); } if (num_symbs > FSE_MAX_SYMBS) { ERROR("Too many symbols for FSE"); } dtable->accuracy_log = accuracy_log; const size_t size = (size_t)1 << accuracy_log; dtable->symbols = malloc(size * sizeof(u8)); dtable->num_bits = malloc(size * sizeof(u8)); dtable->new_state_base = malloc(size * sizeof(u16)); if (!dtable->symbols || !dtable->num_bits || !dtable->new_state_base) { BAD_ALLOC(); } // Used to determine how many bits need to be read for each state, // and where the destination range should start // Needs to be u16 because max value is 2 * max number of symbols, // which can be larger than a byte can store u16 state_desc[FSE_MAX_SYMBS]; // "Symbols are scanned in their natural order for "less than 1" // probabilities. Symbols with this probability are being attributed a // single cell, starting from the end of the table. These symbols define a // full state reset, reading Accuracy_Log bits." int high_threshold = size; for (int s = 0; s < num_symbs; s++) { // Scan for low probability symbols to put at the top if (norm_freqs[s] == -1) { dtable->symbols[--high_threshold] = s; state_desc[s] = 1; } } // "All remaining symbols are sorted in their natural order. Starting from // symbol 0 and table position 0, each symbol gets attributed as many cells // as its probability. Cell allocation is spreaded, not linear." // Place the rest in the table const u16 step = (size >> 1) + (size >> 3) + 3; const u16 mask = size - 1; u16 pos = 0; for (int s = 0; s < num_symbs; s++) { if (norm_freqs[s] <= 0) { continue; } state_desc[s] = norm_freqs[s]; for (int i = 0; i < norm_freqs[s]; i++) { // Give `norm_freqs[s]` states to symbol s dtable->symbols[pos] = s; // "A position is skipped if already occupied, typically by a "less // than 1" probability symbol." do { pos = (pos + step) & mask; } while (pos >= high_threshold); // Note: no other collision checking is necessary as `step` is // coprime to `size`, so the cycle will visit each position exactly // once } } if (pos != 0) { CORRUPTION(); } // Now we can fill baseline and num bits for (size_t i = 0; i < size; i++) { u8 symbol = dtable->symbols[i]; u16 next_state_desc = state_desc[symbol]++; // Fills in the table appropriately, next_state_desc increases by symbol // over time, decreasing number of bits dtable->num_bits[i] = (u8)(accuracy_log - highest_set_bit(next_state_desc)); // Baseline increases until the bit threshold is passed, at which point // it resets to 0 dtable->new_state_base[i] = ((u16)next_state_desc << dtable->num_bits[i]) - size; } } /// Decode an FSE header as defined in the Zstandard format specification and /// use the decoded frequencies to initialize a decoding table. static void FSE_decode_header(FSE_dtable *const dtable, istream_t *const in, const int max_accuracy_log) { // "An FSE distribution table describes the probabilities of all symbols // from 0 to the last present one (included) on a normalized scale of 1 << // Accuracy_Log . // // It's a bitstream which is read forward, in little-endian fashion. It's // not necessary to know its exact size, since it will be discovered and // reported by the decoding process. if (max_accuracy_log > FSE_MAX_ACCURACY_LOG) { ERROR("FSE accuracy too large"); } // The bitstream starts by reporting on which scale it operates. // Accuracy_Log = low4bits + 5. Note that maximum Accuracy_Log for literal // and match lengths is 9, and for offsets is 8. Higher values are // considered errors." const int accuracy_log = 5 + IO_read_bits(in, 4); if (accuracy_log > max_accuracy_log) { ERROR("FSE accuracy too large"); } // "Then follows each symbol value, from 0 to last present one. The number // of bits used by each field is variable. It depends on : // // Remaining probabilities + 1 : example : Presuming an Accuracy_Log of 8, // and presuming 100 probabilities points have already been distributed, the // decoder may read any value from 0 to 255 - 100 + 1 == 156 (inclusive). // Therefore, it must read log2sup(156) == 8 bits. // // Value decoded : small values use 1 less bit : example : Presuming values // from 0 to 156 (inclusive) are possible, 255-156 = 99 values are remaining // in an 8-bits field. They are used this way : first 99 values (hence from // 0 to 98) use only 7 bits, values from 99 to 156 use 8 bits. " i32 remaining = 1 << accuracy_log; i16 frequencies[FSE_MAX_SYMBS]; int symb = 0; while (remaining > 0 && symb < FSE_MAX_SYMBS) { // Log of the number of possible values we could read int bits = highest_set_bit(remaining + 1) + 1; u16 val = IO_read_bits(in, bits); // Try to mask out the lower bits to see if it qualifies for the "small // value" threshold const u16 lower_mask = ((u16)1 << (bits - 1)) - 1; const u16 threshold = ((u16)1 << bits) - 1 - (remaining + 1); if ((val & lower_mask) < threshold) { IO_rewind_bits(in, 1); val = val & lower_mask; } else if (val > lower_mask) { val = val - threshold; } // "Probability is obtained from Value decoded by following formula : // Proba = value - 1" const i16 proba = (i16)val - 1; // "It means value 0 becomes negative probability -1. -1 is a special // probability, which means "less than 1". Its effect on distribution // table is described in next paragraph. For the purpose of calculating // cumulated distribution, it counts as one." remaining -= proba < 0 ? -proba : proba; frequencies[symb] = proba; symb++; // "When a symbol has a probability of zero, it is followed by a 2-bits // repeat flag. This repeat flag tells how many probabilities of zeroes // follow the current one. It provides a number ranging from 0 to 3. If // it is a 3, another 2-bits repeat flag follows, and so on." if (proba == 0) { // Read the next two bits to see how many more 0s int repeat = IO_read_bits(in, 2); while (1) { for (int i = 0; i < repeat && symb < FSE_MAX_SYMBS; i++) { frequencies[symb++] = 0; } if (repeat == 3) { repeat = IO_read_bits(in, 2); } else { break; } } } } IO_align_stream(in); // "When last symbol reaches cumulated total of 1 << Accuracy_Log, decoding // is complete. If the last symbol makes cumulated total go above 1 << // Accuracy_Log, distribution is considered corrupted." if (remaining != 0 || symb >= FSE_MAX_SYMBS) { CORRUPTION(); } // Initialize the decoding table using the determined weights FSE_init_dtable(dtable, frequencies, symb, accuracy_log); } static void FSE_init_dtable_rle(FSE_dtable *const dtable, const u8 symb) { dtable->symbols = malloc(sizeof(u8)); dtable->num_bits = malloc(sizeof(u8)); dtable->new_state_base = malloc(sizeof(u16)); if (!dtable->symbols || !dtable->num_bits || !dtable->new_state_base) { BAD_ALLOC(); } // This setup will always have a state of 0, always return symbol `symb`, // and never consume any bits dtable->symbols[0] = symb; dtable->num_bits[0] = 0; dtable->new_state_base[0] = 0; dtable->accuracy_log = 0; } static void FSE_free_dtable(FSE_dtable *const dtable) { free(dtable->symbols); free(dtable->num_bits); free(dtable->new_state_base); memset(dtable, 0, sizeof(FSE_dtable)); } static void FSE_copy_dtable(FSE_dtable *const dst, const FSE_dtable *const src) { if (src->accuracy_log == 0) { memset(dst, 0, sizeof(FSE_dtable)); return; } size_t size = (size_t)1 << src->accuracy_log; dst->accuracy_log = src->accuracy_log; dst->symbols = malloc(size); dst->num_bits = malloc(size); dst->new_state_base = malloc(size * sizeof(u16)); if (!dst->symbols || !dst->num_bits || !dst->new_state_base) { BAD_ALLOC(); } memcpy(dst->symbols, src->symbols, size); memcpy(dst->num_bits, src->num_bits, size); memcpy(dst->new_state_base, src->new_state_base, size * sizeof(u16)); } /******* END FSE PRIMITIVES ***************************************************/