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Updates to Brotli compression format, decoder and encoder

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This commit contains a batch of changes that were made to the Brotli
compression algorithm in the last month. Most important changes:

   * Fixes to the spec.
   * Change of code length code order.
   * Use a 2-level Huffman lookup table in the decoder.
   * Faster uncompressed meta-block decoding.
   * Optimized encoding of the Huffman code.
   * Detection of UTF-8 input encoding.
   * UTF-8 based literal cost modeling for improved
     backward reference selection.
This commit is contained in:
Zoltan Szabadka 2014-02-14 15:04:23 +01:00
parent d01c71c4ad
commit 0454ab4ec0
16 changed files with 912 additions and 635 deletions
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25
brotlispec.txt
View File

@ -498,11 +498,11 @@ Abstract
Symbol Code
------ ----
0 00
1 1010
2 100
3 11
4 01
5 1011
1 1110
2 110
3 01
4 10
5 1111
We can now define the format of the complex Huffman code as
follows:
@ -513,7 +513,7 @@ Abstract
Code lengths for symbols in the code length alphabet given
just above, in the order: 1, 2, 3, 4, 0, 17, 5, 6, 16, 7,
just above, in the order: 1, 2, 3, 4, 0, 5, 17, 6, 16, 7,
8, 9, 10, 11, 12, 13, 14, 15
The code lengths of code length symbols are between 0 and
@ -572,7 +572,7 @@ Abstract
6: last distance - 2
7: last distance + 2
8: last distance - 3
9: last disatnce + 3
9: last distance + 3
10: second last distance - 1
11: second last distance + 1
12: second last distance - 2
@ -647,7 +647,7 @@ Abstract
---- ---- ------ ---- ---- ------- ---- ---- -------
0 0 0 8 2 10-13 16 6 130-193
1 0 1 9 2 14-17 17 7 194-321
2 0 2 10 3 18-25 18 8 322-527
2 0 2 10 3 18-25 18 8 322-577
3 0 3 11 3 26-33 19 9 578-1089
4 0 4 12 4 34-49 20 10 1090-2113
5 0 5 13 4 50-65 21 12 2114-6209
@ -681,7 +681,7 @@ Abstract
| | |
+---------+---------+---------+
| | | |
0-7 | 128-191 | 192-255 | 383-447 |
0-7 | 128-191 | 192-255 | 384-447 |
| | | |
+---------+---------+---------+
| | | |
@ -689,7 +689,7 @@ Abstract
| | | |
+---------+---------+---------+
| | | |
16-23 | 448-551 | 576-639 | 640-703 |
16-23 | 448-511 | 576-639 | 640-703 |
| | | |
+---------+---------+---------+
@ -1008,9 +1008,10 @@ Abstract
1 bit: ISEMPTY, set to 1 if the meta-block is empty, this
field is only present if ISLAST bit is set, since
only the last meta-block can be empty
2 bits: MNIBBLES, (# of nibbles to represent the length) - 4
2 bits: MNIBBLES - 4, where MNIBBLES is # of nibbles to represent
the length
(MNIBBLES + 4) x 4 bits: MLEN - 1, where MLEN is the length
MNIBBLES x 4 bits: MLEN - 1, where MLEN is the length
of the meta-block in the input data in bytes
1 bit: ISUNCOMPRESSED, if set to 1, any bits of input up to

4
dec/bit_reader.c
View File

@ -33,7 +33,7 @@ int BrotliInitBitReader(BrotliBitReader* const br, BrotliInput input) {
br->val_ = 0;
br->pos_ = 0;
br->bit_pos_ = 0;
br->bits_left_ = 64;
br->bit_end_pos_ = 0;
br->eos_ = 0;
if (!BrotliReadMoreInput(br)) {
return 0;
@ -42,7 +42,7 @@ int BrotliInitBitReader(BrotliBitReader* const br, BrotliInput input) {
br->val_ |= ((uint64_t)br->buf_[br->pos_]) << (8 * i);
++br->pos_;
}
return (br->bits_left_ > 64);
return (br->bit_end_pos_ > 0);
}
#if defined(__cplusplus) || defined(c_plusplus)

31
dec/bit_reader.h
View File

@ -31,7 +31,7 @@ extern "C" {
#define BROTLI_IBUF_SIZE (2 * BROTLI_READ_SIZE + 32)
#define BROTLI_IBUF_MASK (2 * BROTLI_READ_SIZE - 1)
#define UNALIGNED_COPY64(dst, src) *(uint64_t*)(dst) = *(const uint64_t*)(src)
#define UNALIGNED_COPY64(dst, src) memcpy(dst, src, 8)
static const uint32_t kBitMask[BROTLI_MAX_NUM_BIT_READ] = {
0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767,
@ -42,13 +42,13 @@ typedef struct {
/* Input byte buffer, consist of a ringbuffer and a "slack" region where */
/* bytes from the start of the ringbuffer are copied. */
uint8_t buf_[BROTLI_IBUF_SIZE];
uint8_t* buf_ptr_; /* next input will write here */
BrotliInput input_; /* input callback */
uint64_t val_; /* pre-fetched bits */
uint32_t pos_; /* byte position in stream */
uint32_t bit_pos_; /* current bit-reading position in val_ */
uint32_t bits_left_; /* how many valid bits left */
int eos_; /* input stream is finished */
uint8_t* buf_ptr_; /* next input will write here */
BrotliInput input_; /* input callback */
uint64_t val_; /* pre-fetched bits */
uint32_t pos_; /* byte position in stream */
uint32_t bit_pos_; /* current bit-reading position in val_ */
uint32_t bit_end_pos_; /* bit-reading end position from LSB of val_ */
int eos_; /* input stream is finished */
} BrotliBitReader;
int BrotliInitBitReader(BrotliBitReader* const br, BrotliInput input);
@ -65,7 +65,7 @@ static BROTLI_INLINE void BrotliSetBitPos(BrotliBitReader* const br,
#ifdef BROTLI_DECODE_DEBUG
uint32_t n_bits = val - br->bit_pos_;
const uint32_t bval = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
printf("[BrotliReadBits] %010ld %2d val: %6x\n",
printf("[BrotliReadBits] %010d %2d val: %6x\n",
(br->pos_ << 3) + br->bit_pos_ - 64, n_bits, bval);
#endif
br->bit_pos_ = val;
@ -78,7 +78,7 @@ static BROTLI_INLINE void ShiftBytes(BrotliBitReader* const br) {
br->val_ |= ((uint64_t)br->buf_[br->pos_ & BROTLI_IBUF_MASK]) << 56;
++br->pos_;
br->bit_pos_ -= 8;
br->bits_left_ -= 8;
br->bit_end_pos_ -= 8;
}
}
@ -95,10 +95,10 @@ static BROTLI_INLINE void ShiftBytes(BrotliBitReader* const br) {
every 32 bytes of input is read.
*/
static BROTLI_INLINE int BrotliReadMoreInput(BrotliBitReader* const br) {
if (br->bits_left_ > 320) {
if (br->bit_end_pos_ > 256) {
return 1;
} else if (br->eos_) {
return br->bit_pos_ <= br->bits_left_;
return br->bit_pos_ <= br->bit_end_pos_;
} else {
uint8_t* dst = br->buf_ptr_;
int bytes_read = BrotliRead(br->input_, dst, BROTLI_READ_SIZE);
@ -131,7 +131,7 @@ static BROTLI_INLINE int BrotliReadMoreInput(BrotliBitReader* const br) {
} else {
br->buf_ptr_ = br->buf_;
}
br->bits_left_ += ((uint32_t)bytes_read << 3);
br->bit_end_pos_ += ((uint32_t)bytes_read << 3);
return 1;
}
}
@ -147,7 +147,7 @@ static BROTLI_INLINE void BrotliFillBitWindow(BrotliBitReader* const br) {
br->buf_ + (br->pos_ & BROTLI_IBUF_MASK)) << 24;
br->pos_ += 5;
br->bit_pos_ -= 40;
br->bits_left_ -= 40;
br->bit_end_pos_ -= 40;
#else
ShiftBytes(br);
#endif
@ -155,14 +155,13 @@ static BROTLI_INLINE void BrotliFillBitWindow(BrotliBitReader* const br) {
}
/* Reads the specified number of bits from Read Buffer. */
/* Requires that n_bits is positive. */
static BROTLI_INLINE uint32_t BrotliReadBits(
BrotliBitReader* const br, int n_bits) {
uint32_t val;
BrotliFillBitWindow(br);
val = (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
#ifdef BROTLI_DECODE_DEBUG
printf("[BrotliReadBits] %010ld %2d val: %6x\n",
printf("[BrotliReadBits] %010d %2d val: %6x\n",
(br->pos_ << 3) + br->bit_pos_ - 64, n_bits, val);
#endif
br->bit_pos_ += (uint32_t)n_bits;

538
dec/decode.c
View File

@ -46,9 +46,14 @@ static const int kNumBlockLengthCodes = 26;
static const int kLiteralContextBits = 6;
static const int kDistanceContextBits = 2;
#define HUFFMAN_TABLE_BITS 8
#define HUFFMAN_TABLE_MASK 0xff
/* This is a rough estimate, not an exact bound. */
#define HUFFMAN_MAX_TABLE_SIZE 2048
#define CODE_LENGTH_CODES 18
static const uint8_t kCodeLengthCodeOrder[CODE_LENGTH_CODES] = {
1, 2, 3, 4, 0, 17, 5, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15,
1, 2, 3, 4, 0, 5, 17, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15,
};
#define NUM_DISTANCE_SHORT_CODES 16
@ -104,36 +109,19 @@ static void DecodeMetaBlockLength(BrotliBitReader* br,
}
/* Decodes the next Huffman code from bit-stream. */
static BROTLI_INLINE int ReadSymbol(const HuffmanTree* tree,
static BROTLI_INLINE int ReadSymbol(const HuffmanCode* table,
BrotliBitReader* br) {
uint32_t bits;
uint32_t bitpos;
int lut_ix;
uint8_t lut_bits;
const HuffmanTreeNode* node = tree->root_;
int nbits;
BrotliFillBitWindow(br);
bits = BrotliPrefetchBits(br);
bitpos = br->bit_pos_;
/* Check if we find the bit combination from the Huffman lookup table. */
lut_ix = bits & (HUFF_LUT - 1);
lut_bits = tree->lut_bits_[lut_ix];
if (lut_bits <= HUFF_LUT_BITS) {
BrotliSetBitPos(br, bitpos + lut_bits);
return tree->lut_symbol_[lut_ix];
table += (int)(br->val_ >> br->bit_pos_) & HUFFMAN_TABLE_MASK;
nbits = table->bits - HUFFMAN_TABLE_BITS;
if (nbits > 0) {
br->bit_pos_ += HUFFMAN_TABLE_BITS;
table += table->value;
table += (int)(br->val_ >> br->bit_pos_) & ((1 << nbits) - 1);
}
node += tree->lut_jump_[lut_ix];
bitpos += HUFF_LUT_BITS;
bits >>= HUFF_LUT_BITS;
/* Decode the value from a binary tree. */
assert(node != NULL);
do {
node = HuffmanTreeNextNode(node, bits & 1);
bits >>= 1;
++bitpos;
} while (HuffmanTreeNodeIsNotLeaf(node));
BrotliSetBitPos(br, bitpos);
return node->symbol_;
br->bit_pos_ += table->bits;
return table->value;
}
static void PrintUcharVector(const uint8_t* v, int len) {
@ -145,47 +133,34 @@ static int ReadHuffmanCodeLengths(
const uint8_t* code_length_code_lengths,
int num_symbols, uint8_t* code_lengths,
BrotliBitReader* br) {
int ok = 0;
int symbol;
int symbol = 0;
uint8_t prev_code_len = kDefaultCodeLength;
int repeat = 0;
uint8_t repeat_length = 0;
uint8_t repeat_code_len = 0;
int space = 32768;
HuffmanTree tree;
HuffmanCode table[32];
if (!BrotliHuffmanTreeBuildImplicit(&tree, code_length_code_lengths,
CODE_LENGTH_CODES)) {
if (!BrotliBuildHuffmanTable(table, 5,
code_length_code_lengths,
CODE_LENGTH_CODES)) {
printf("[ReadHuffmanCodeLengths] Building code length tree failed: ");
PrintUcharVector(code_length_code_lengths, CODE_LENGTH_CODES);
return 0;
}
if (!BrotliReadMoreInput(br)) {
printf("[ReadHuffmanCodeLengths] Unexpected end of input.\n");
return 0;
}
symbol = 0;
while (symbol + repeat < num_symbols && space > 0) {
while (symbol < num_symbols && space > 0) {
const HuffmanCode* p = table;
uint8_t code_len;
if (!BrotliReadMoreInput(br)) {
printf("[ReadHuffmanCodeLengths] Unexpected end of input.\n");
goto End;
}
code_len = (uint8_t)ReadSymbol(&tree, br);
BROTLI_LOG_UINT(symbol);
BROTLI_LOG_UINT(repeat);
BROTLI_LOG_UINT(repeat_length);
BROTLI_LOG_UINT(code_len);
if ((code_len < kCodeLengthRepeatCode) ||
(code_len == kCodeLengthRepeatCode && repeat_length == 0) ||
(code_len > kCodeLengthRepeatCode && repeat_length > 0)) {
while (repeat > 0) {
code_lengths[symbol++] = repeat_length;
--repeat;
}
return 0;
}
BrotliFillBitWindow(br);
p += (br->val_ >> br->bit_pos_) & 31;
br->bit_pos_ += p->bits;
code_len = (uint8_t)p->value;
if (code_len < kCodeLengthRepeatCode) {
repeat = 0;
code_lengths[symbol++] = code_len;
if (code_len != 0) {
prev_code_len = code_len;
@ -193,47 +168,46 @@ static int ReadHuffmanCodeLengths(
}
} else {
const int extra_bits = code_len - 14;
int i = repeat;
int old_repeat;
int repeat_delta;
uint8_t new_len = 0;
if (code_len == kCodeLengthRepeatCode) {
new_len = prev_code_len;
}
if (repeat_code_len != new_len) {
repeat = 0;
repeat_code_len = new_len;
}
old_repeat = repeat;
if (repeat > 0) {
repeat -= 2;
repeat <<= extra_bits;
}
repeat += (int)BrotliReadBits(br, extra_bits) + 3;
if (repeat + symbol > num_symbols) {
goto End;
repeat_delta = repeat - old_repeat;
if (symbol + repeat_delta > num_symbols) {
return 0;
}
if (code_len == kCodeLengthRepeatCode) {
repeat_length = prev_code_len;
for (; i < repeat; ++i) {
space -= 32768 >> repeat_length;
}
} else {
repeat_length = 0;
memset(&code_lengths[symbol], repeat_code_len, (size_t)repeat_delta);
symbol += repeat_delta;
if (repeat_code_len != 0) {
space -= repeat_delta << (15 - repeat_code_len);
}
}
}
if (space != 0) {
printf("[ReadHuffmanCodeLengths] space = %d\n", space);
goto End;
return 0;
}
if (symbol + repeat > num_symbols) {
printf("[ReadHuffmanCodeLengths] symbol + repeat > num_symbols "
"(%d + %d vs %d)\n", symbol, repeat, num_symbols);
goto End;
}
while (repeat-- > 0) code_lengths[symbol++] = repeat_length;
while (symbol < num_symbols) code_lengths[symbol++] = 0;
ok = 1;
End:
BrotliHuffmanTreeRelease(&tree);
return ok;
memset(&code_lengths[symbol], 0, (size_t)(num_symbols - symbol));
return 1;
}
static int ReadHuffmanCode(int alphabet_size,
HuffmanTree* tree,
HuffmanCode* table,
BrotliBitReader* br) {
int ok = 1;
int table_size = 0;
int simple_code_or_skip;
uint8_t* code_lengths = NULL;
@ -290,109 +264,49 @@ static int ReadHuffmanCode(int alphabet_size,
int i;
uint8_t code_length_code_lengths[CODE_LENGTH_CODES] = { 0 };
int space = 32;
for (i = simple_code_or_skip;
i < CODE_LENGTH_CODES && space > 0; ++i) {
int code_len_idx = kCodeLengthCodeOrder[i];
uint8_t v = (uint8_t)BrotliReadBits(br, 2);
if (v == 1) {
v = (uint8_t)BrotliReadBits(br, 1);
if (v == 0) {
v = 2;
} else {
v = (uint8_t)BrotliReadBits(br, 1);
if (v == 0) {
v = 1;
} else {
v = 5;
}
}
} else if (v == 2) {
v = 4;
}
/* Static Huffman code for the code length code lengths */
static const HuffmanCode huff[16] = {
{2, 0}, {2, 4}, {2, 3}, {3, 2}, {2, 0}, {2, 4}, {2, 3}, {4, 1},
{2, 0}, {2, 4}, {2, 3}, {3, 2}, {2, 0}, {2, 4}, {2, 3}, {4, 5},
};
for (i = simple_code_or_skip; i < CODE_LENGTH_CODES && space > 0; ++i) {
const int code_len_idx = kCodeLengthCodeOrder[i];
const HuffmanCode* p = huff;
uint8_t v;
BrotliFillBitWindow(br);
p += (br->val_ >> br->bit_pos_) & 15;
br->bit_pos_ += p->bits;
v = (uint8_t)p->value;
code_length_code_lengths[code_len_idx] = v;
BROTLI_LOG_ARRAY_INDEX(code_length_code_lengths, code_len_idx);
if (v != 0) {
space -= (32 >> v);
}
}
ok = ReadHuffmanCodeLengths(code_length_code_lengths, alphabet_size,
code_lengths, br);
ok = ReadHuffmanCodeLengths(code_length_code_lengths,
alphabet_size, code_lengths, br);
}
if (ok) {
ok = BrotliHuffmanTreeBuildImplicit(tree, code_lengths, alphabet_size);
if (!ok) {
printf("[ReadHuffmanCode] HuffmanTreeBuildImplicit failed: ");
table_size = BrotliBuildHuffmanTable(table, HUFFMAN_TABLE_BITS,
code_lengths, alphabet_size);
if (table_size == 0) {
printf("[ReadHuffmanCode] BuildHuffmanTable failed: ");
PrintUcharVector(code_lengths, alphabet_size);
}
}
free(code_lengths);
return ok;
return table_size;
}
static int ReadCopyDistance(const HuffmanTree* tree,
int num_direct_codes,
int postfix_bits,
int postfix_mask,
BrotliBitReader* br) {
static BROTLI_INLINE int ReadBlockLength(const HuffmanCode* table,
BrotliBitReader* br) {
int code;
int nbits;
int postfix;
int offset;
code = ReadSymbol(tree, br);
if (code < num_direct_codes) {
return code;
}
code -= num_direct_codes;
postfix = code & postfix_mask;
code >>= postfix_bits;
nbits = (code >> 1) + 1;
offset = ((2 + (code & 1)) << nbits) - 4;
return (num_direct_codes +
((offset + (int)BrotliReadBits(br, nbits)) << postfix_bits) +
postfix);
}
static int ReadBlockLength(const HuffmanTree* tree, BrotliBitReader* br) {
int code;
int nbits;
code = ReadSymbol(tree, br);
code = ReadSymbol(table, br);
nbits = kBlockLengthPrefixCode[code].nbits;
return kBlockLengthPrefixCode[code].offset + (int)BrotliReadBits(br, nbits);
}
static void ReadInsertAndCopy(const HuffmanTree* tree,
int* insert_len,
int* copy_len,
int* copy_dist,
BrotliBitReader* br) {
int code;
int range_idx;
int insert_code;
int insert_extra_bits;
int copy_code;
int copy_extra_bits;
code = ReadSymbol(tree, br);
range_idx = code >> 6;
if (range_idx >= 2) {
range_idx -= 2;
*copy_dist = -1;
} else {
*copy_dist = 0;
}
insert_code = kInsertRangeLut[range_idx] + ((code >> 3) & 7);
copy_code = kCopyRangeLut[range_idx] + (code & 7);
*insert_len = kInsertLengthPrefixCode[insert_code].offset;
insert_extra_bits = kInsertLengthPrefixCode[insert_code].nbits;
if (insert_extra_bits > 0) {
*insert_len += (int)BrotliReadBits(br, insert_extra_bits);
}
*copy_len = kCopyLengthPrefixCode[copy_code].offset;
copy_extra_bits = kCopyLengthPrefixCode[copy_code].nbits;
if (copy_extra_bits > 0) {
*copy_len += (int)BrotliReadBits(br, copy_extra_bits);
}
}
static int TranslateShortCodes(int code, int* ringbuffer, int index) {
int val;
if (code < NUM_DISTANCE_SHORT_CODES) {
@ -429,24 +343,22 @@ static void InverseMoveToFrontTransform(uint8_t* v, int v_len) {
typedef struct {
int alphabet_size;
int num_htrees;
HuffmanTree* htrees;
HuffmanCode* codes;
HuffmanCode** htrees;
} HuffmanTreeGroup;
static void HuffmanTreeGroupInit(HuffmanTreeGroup* group, int alphabet_size,
int ntrees) {
int i;
group->alphabet_size = alphabet_size;
group->num_htrees = ntrees;
group->htrees = (HuffmanTree*)malloc(sizeof(HuffmanTree) * (size_t)ntrees);
for (i = 0; i < ntrees; ++i) {
group->htrees[i].root_ = NULL;
}
group->codes = (HuffmanCode*)malloc(
sizeof(HuffmanCode) * (size_t)(ntrees * HUFFMAN_MAX_TABLE_SIZE));
group->htrees = (HuffmanCode**)malloc(sizeof(HuffmanCode*) * (size_t)ntrees);
}
static void HuffmanTreeGroupRelease(HuffmanTreeGroup* group) {
int i;
for (i = 0; i < group->num_htrees; ++i) {
BrotliHuffmanTreeRelease(&group->htrees[i]);
if (group->codes) {
free(group->codes);
}
if (group->htrees) {
free(group->htrees);
@ -456,8 +368,13 @@ static void HuffmanTreeGroupRelease(HuffmanTreeGroup* group) {
static int HuffmanTreeGroupDecode(HuffmanTreeGroup* group,
BrotliBitReader* br) {
int i;
int table_size;
HuffmanCode* next = group->codes;
for (i = 0; i < group->num_htrees; ++i) {
if (!ReadHuffmanCode(group->alphabet_size, &group->htrees[i], br)) {
group->htrees[i] = next;
table_size = ReadHuffmanCode(group->alphabet_size, next, br);
next += table_size;
if (table_size == 0) {
return 0;
}
}
@ -469,6 +386,10 @@ static int DecodeContextMap(int context_map_size,
uint8_t** context_map,
BrotliBitReader* br) {
int ok = 1;
int use_rle_for_zeros;
int max_run_length_prefix = 0;
HuffmanCode* table;
int i;
if (!BrotliReadMoreInput(br)) {
printf("[DecodeContextMap] Unexpected end of input.\n");
return 0;
@ -487,55 +408,54 @@ static int DecodeContextMap(int context_map_size,
return 1;
}
{
HuffmanTree tree_index_htree;
int use_rle_for_zeros = (int)BrotliReadBits(br, 1);
int max_run_length_prefix = 0;
int i;
if (use_rle_for_zeros) {
max_run_length_prefix = (int)BrotliReadBits(br, 4) + 1;
use_rle_for_zeros = (int)BrotliReadBits(br, 1);
if (use_rle_for_zeros) {
max_run_length_prefix = (int)BrotliReadBits(br, 4) + 1;
}
table = (HuffmanCode*)malloc(HUFFMAN_MAX_TABLE_SIZE * sizeof(*table));
if (table == NULL) {
return 0;
}
if (!ReadHuffmanCode(*num_htrees + max_run_length_prefix, table, br)) {
ok = 0;
goto End;
}
for (i = 0; i < context_map_size;) {
int code;
if (!BrotliReadMoreInput(br)) {
printf("[DecodeContextMap] Unexpected end of input.\n");
ok = 0;
goto End;
}
if (!ReadHuffmanCode(*num_htrees + max_run_length_prefix,
&tree_index_htree, br)) {
return 0;
}
for (i = 0; i < context_map_size;) {
int code;
if (!BrotliReadMoreInput(br)) {
printf("[DecodeContextMap] Unexpected end of input.\n");
ok = 0;
goto End;
}
code = ReadSymbol(&tree_index_htree, br);
if (code == 0) {
code = ReadSymbol(table, br);
if (code == 0) {
(*context_map)[i] = 0;
++i;
} else if (code <= max_run_length_prefix) {
int reps = 1 + (1 << code) + (int)BrotliReadBits(br, code);
while (--reps) {
if (i >= context_map_size) {
ok = 0;
goto End;
}
(*context_map)[i] = 0;
++i;
} else if (code <= max_run_length_prefix) {
int reps = 1 + (1 << code) + (int)BrotliReadBits(br, code);
while (--reps) {
if (i >= context_map_size) {
ok = 0;
goto End;
}
(*context_map)[i] = 0;
++i;
}
} else {
(*context_map)[i] = (uint8_t)(code - max_run_length_prefix);
++i;
}
} else {
(*context_map)[i] = (uint8_t)(code - max_run_length_prefix);
++i;
}
End:
BrotliHuffmanTreeRelease(&tree_index_htree);
}
if (BrotliReadBits(br, 1)) {
InverseMoveToFrontTransform(*context_map, context_map_size);
}
End:
free(table);
return ok;
}
static BROTLI_INLINE void DecodeBlockType(const int max_block_type,
const HuffmanTree* trees,
const HuffmanCode* trees,
int tree_type,
int* block_types,
int* ringbuffers,
@ -543,7 +463,7 @@ static BROTLI_INLINE void DecodeBlockType(const int max_block_type,
BrotliBitReader* br) {
int* ringbuffer = ringbuffers + tree_type * 2;
int* index = indexes + tree_type;
int type_code = ReadSymbol(trees + tree_type, br);
int type_code = ReadSymbol(&trees[tree_type * HUFFMAN_MAX_TABLE_SIZE], br);
int block_type;
if (type_code == 0) {
block_type = ringbuffer[*index & 1];
@ -608,6 +528,92 @@ static BROTLI_INLINE void IncrementalCopyFastPath(
}
}
int CopyUncompressedBlockToOutput(BrotliOutput output, int len, int pos,
uint8_t* ringbuffer, int ringbuffer_mask,
BrotliBitReader* br) {
const int rb_size = ringbuffer_mask + 1;
uint8_t* ringbuffer_end = ringbuffer + rb_size;
int rb_pos = pos & ringbuffer_mask;
int br_pos = br->pos_ & BROTLI_IBUF_MASK;
int nbytes;
/* For short lengths copy byte-by-byte */
if (len < 8 || br->bit_pos_ + (uint32_t)(len << 3) < br->bit_end_pos_) {
while (len-- > 0) {
if (!BrotliReadMoreInput(br)) {
return 0;
}
ringbuffer[rb_pos++]= (uint8_t)BrotliReadBits(br, 8);
if (rb_pos == rb_size) {
if (BrotliWrite(output, ringbuffer, (size_t)rb_size) < rb_size) {
return 0;
}
rb_pos = 0;
}
}
return 1;
}
if (br->bit_end_pos_ < 64) {
return 0;
}
/* Copy remaining 0-8 bytes from br->val_ to ringbuffer. */
while (br->bit_pos_ < 64) {
ringbuffer[rb_pos] = (uint8_t)(br->val_ >> br->bit_pos_);
br->bit_pos_ += 8;
++rb_pos;
--len;
}
/* Copy remaining bytes from br->buf_ to ringbuffer. */
nbytes = (int)(br->bit_end_pos_ - br->bit_pos_) >> 3;
if (br_pos + nbytes > BROTLI_IBUF_MASK) {
int tail = BROTLI_IBUF_MASK + 1 - br_pos;
memcpy(&ringbuffer[rb_pos], &br->buf_[br_pos], (size_t)tail);
nbytes -= tail;
rb_pos += tail;
len -= tail;
br_pos = 0;
}
memcpy(&ringbuffer[rb_pos], &br->buf_[br_pos], (size_t)nbytes);
rb_pos += nbytes;
len -= nbytes;
/* If we wrote past the logical end of the ringbuffer, copy the tail of the
ringbuffer to its beginning and flush the ringbuffer to the output. */
if (rb_pos >= rb_size) {
if (BrotliWrite(output, ringbuffer, (size_t)rb_size) < rb_size) {
return 0;
}
rb_pos -= rb_size;
memcpy(ringbuffer, ringbuffer_end, (size_t)rb_pos);
}
/* If we have more to copy than the remaining size of the ringbuffer, then we
first fill the ringbuffer from the input and then flush the ringbuffer to
the output */
while (rb_pos + len >= rb_size) {
nbytes = rb_size - rb_pos;
if (BrotliRead(br->input_, &ringbuffer[rb_pos], (size_t)nbytes) < nbytes ||
BrotliWrite(output, ringbuffer, (size_t)rb_size) < nbytes) {
return 0;
}
len -= nbytes;
rb_pos = 0;
}
/* Copy straight from the input onto the ringbuffer. The ringbuffer will be
flushed to the output at a later time. */
if (BrotliRead(br->input_, &ringbuffer[rb_pos], (size_t)len) < len) {
return 0;
}
/* Restore the state of the bit reader. */
BrotliInitBitReader(br, br->input_);
return 1;
}
int BrotliDecompressedSize(size_t encoded_size,
const uint8_t* encoded_buffer,
size_t* decoded_size) {
@ -662,11 +668,15 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
uint8_t prev_byte1 = 0;
uint8_t prev_byte2 = 0;
HuffmanTreeGroup hgroup[3];
HuffmanCode* block_type_trees = NULL;
HuffmanCode* block_len_trees = NULL;
BrotliBitReader br;
/* 16 bytes would be enough, but we add some more slack for transforms */
/* to work at the end of the ringbuffer. */
static const int kRingBufferWriteAheadSlack = 128;
/* We need the slack region for the following reasons:
- always doing two 8-byte copies for fast backward copying
- transforms
- flushing the input ringbuffer when decoding uncompressed blocks */
static const int kRingBufferWriteAheadSlack = 128 + BROTLI_READ_SIZE;
static const int kMaxDictionaryWordLength = 0;
@ -688,6 +698,16 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
}
ringbuffer_end = ringbuffer + ringbuffer_size;
if (ok) {
block_type_trees = (HuffmanCode*)malloc(
3 * HUFFMAN_MAX_TABLE_SIZE * sizeof(HuffmanCode));
block_len_trees = (HuffmanCode*)malloc(
3 * HUFFMAN_MAX_TABLE_SIZE * sizeof(HuffmanCode));
if (block_type_trees == NULL || block_len_trees == NULL) {
ok = 0;
}
}
while (!input_end && ok) {
int meta_block_remaining_len = 0;
int is_uncompressed;
@ -696,8 +716,6 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
int num_block_types[3] = { 1, 1, 1 };
int block_type_rb[6] = { 0, 1, 0, 1, 0, 1 };
int block_type_rb_index[3] = { 0 };
HuffmanTree block_type_trees[3];
HuffmanTree block_len_trees[3];
int distance_postfix_bits;
int num_direct_distance_codes;
int distance_postfix_mask;
@ -716,12 +734,11 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
int context_lookup_offset1 = 0;
int context_lookup_offset2 = 0;
uint8_t context_mode;
HuffmanCode* htree_command;
for (i = 0; i < 3; ++i) {
hgroup[i].num_htrees = 0;
hgroup[i].codes = NULL;
hgroup[i].htrees = NULL;
block_type_trees[i].root_ = NULL;
block_len_trees[i].root_ = NULL;
}
if (!BrotliReadMoreInput(&br)) {
@ -738,31 +755,25 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
}
if (is_uncompressed) {
BrotliSetBitPos(&br, (br.bit_pos_ + 7) & (uint32_t)(~7UL));
while (meta_block_remaining_len) {
ringbuffer[pos & ringbuffer_mask] = (uint8_t)BrotliReadBits(&br, 8);
if ((pos & ringbuffer_mask) == ringbuffer_mask) {
if (BrotliWrite(output, ringbuffer, (size_t)ringbuffer_size) < 0) {
ok = 0;
goto End;
}
}
++pos;
--meta_block_remaining_len;
}
ok = CopyUncompressedBlockToOutput(output, meta_block_remaining_len, pos,
ringbuffer, ringbuffer_mask, &br);
pos += meta_block_remaining_len;
goto End;
}
for (i = 0; i < 3; ++i) {
block_type_trees[i].root_ = NULL;
block_len_trees[i].root_ = NULL;
num_block_types[i] = DecodeVarLenUint8(&br) + 1;
if (num_block_types[i] >= 2) {
if (!ReadHuffmanCode(
num_block_types[i] + 2, &block_type_trees[i], &br) ||
!ReadHuffmanCode(kNumBlockLengthCodes, &block_len_trees[i], &br)) {
if (!ReadHuffmanCode(num_block_types[i] + 2,
&block_type_trees[i * HUFFMAN_MAX_TABLE_SIZE],
&br) ||
!ReadHuffmanCode(kNumBlockLengthCodes,
&block_len_trees[i * HUFFMAN_MAX_TABLE_SIZE],
&br)) {
ok = 0;
goto End;
}
block_length[i] = ReadBlockLength(&block_len_trees[i], &br);
block_length[i] = ReadBlockLength(
&block_len_trees[i * HUFFMAN_MAX_TABLE_SIZE], &br);
block_type_rb_index[i] = 1;
}
}
@ -822,8 +833,13 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
context_mode = context_modes[block_type[0]];
context_lookup_offset1 = kContextLookupOffsets[context_mode];
context_lookup_offset2 = kContextLookupOffsets[context_mode + 1];
htree_command = hgroup[1].htrees[0];
while (meta_block_remaining_len > 0) {
int cmd_code;
int range_idx;
int insert_code;
int copy_code;
int insert_length;
int copy_length;
int distance_code;
@ -841,11 +857,25 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
DecodeBlockType(num_block_types[1],
block_type_trees, 1, block_type, block_type_rb,
block_type_rb_index, &br);
block_length[1] = ReadBlockLength(&block_len_trees[1], &br);
block_length[1] = ReadBlockLength(
&block_len_trees[HUFFMAN_MAX_TABLE_SIZE], &br);
htree_command = hgroup[1].htrees[block_type[1]];
}
--block_length[1];
ReadInsertAndCopy(&hgroup[1].htrees[block_type[1]],
&insert_length, &copy_length, &distance_code, &br);
cmd_code = ReadSymbol(htree_command, &br);
range_idx = cmd_code >> 6;
if (range_idx >= 2) {
range_idx -= 2;
distance_code = -1;
} else {
distance_code = 0;
}
insert_code = kInsertRangeLut[range_idx] + ((cmd_code >> 3) & 7);
copy_code = kCopyRangeLut[range_idx] + (cmd_code & 7);
insert_length = kInsertLengthPrefixCode[insert_code].offset +
(int)BrotliReadBits(&br, kInsertLengthPrefixCode[insert_code].nbits);
copy_length = kCopyLengthPrefixCode[copy_code].offset +
(int)BrotliReadBits(&br, kCopyLengthPrefixCode[copy_code].nbits);
BROTLI_LOG_UINT(insert_length);
BROTLI_LOG_UINT(copy_length);
BROTLI_LOG_UINT(distance_code);
@ -859,7 +889,7 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
DecodeBlockType(num_block_types[0],
block_type_trees, 0, block_type, block_type_rb,
block_type_rb_index, &br);
block_length[0] = ReadBlockLength(&block_len_trees[0], &br);
block_length[0] = ReadBlockLength(block_len_trees, &br);
context_offset = block_type[0] << kLiteralContextBits;
context_map_slice = context_map + context_offset;
context_mode = context_modes[block_type[0]];
@ -872,7 +902,7 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
literal_htree_index = context_map_slice[context];
--block_length[0];
prev_byte2 = prev_byte1;
prev_byte1 = (uint8_t)ReadSymbol(&hgroup[0].htrees[literal_htree_index],
prev_byte1 = (uint8_t)ReadSymbol(hgroup[0].htrees[literal_htree_index],
&br);
ringbuffer[pos & ringbuffer_mask] = prev_byte1;
BROTLI_LOG_UINT(literal_htree_index);
@ -899,7 +929,8 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
DecodeBlockType(num_block_types[2],
block_type_trees, 2, block_type, block_type_rb,
block_type_rb_index, &br);
block_length[2] = ReadBlockLength(&block_len_trees[2], &br);
block_length[2] = ReadBlockLength(
&block_len_trees[2 * HUFFMAN_MAX_TABLE_SIZE], &br);
dist_htree_index = (uint8_t)block_type[2];
dist_context_offset = block_type[2] << kDistanceContextBits;
dist_context_map_slice = dist_context_map + dist_context_offset;
@ -907,11 +938,20 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
--block_length[2];
context = (uint8_t)(copy_length > 4 ? 3 : copy_length - 2);
dist_htree_index = dist_context_map_slice[context];
distance_code = ReadCopyDistance(&hgroup[2].htrees[dist_htree_index],
num_direct_distance_codes,
distance_postfix_bits,
distance_postfix_mask,
&br);
distance_code = ReadSymbol(hgroup[2].htrees[dist_htree_index], &br);
if (distance_code >= num_direct_distance_codes) {
int nbits;
int postfix;
int offset;
distance_code -= num_direct_distance_codes;
postfix = distance_code & distance_postfix_mask;
distance_code >>= distance_postfix_bits;
nbits = (distance_code >> 1) + 1;
offset = ((2 + (distance_code & 1)) << nbits) - 4;
distance_code = num_direct_distance_codes +
((offset + (int)BrotliReadBits(&br, nbits)) <<
distance_postfix_bits) + postfix;
}
}
/* Convert the distance code to the actual distance by possibly looking */
@ -1004,8 +1044,6 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
}
for (i = 0; i < 3; ++i) {
HuffmanTreeGroupRelease(&hgroup[i]);
BrotliHuffmanTreeRelease(&block_type_trees[i]);
BrotliHuffmanTreeRelease(&block_len_trees[i]);
}
}
@ -1015,6 +1053,12 @@ int BrotliDecompress(BrotliInput input, BrotliOutput output) {
}
free(ringbuffer);
}
if (block_type_trees != 0) {
free(block_type_trees);
}
if (block_len_trees != 0) {
free(block_len_trees);
}
return ok;
}

2
dec/decode.h
View File

@ -26,6 +26,8 @@ extern "C" {
#endif
/* Sets *decoded_size to the decompressed size of the given encoded stream. */
/* This function only works if the encoded buffer has a single meta block, */
/* and this meta block must have the "is last" bit set. */
/* Returns 1 on success, 0 on failure. */
int BrotliDecompressedSize(size_t encoded_size,
const uint8_t* encoded_buffer,

309
dec/huffman.c
View File

@ -12,11 +12,12 @@
See the License for the specific language governing permissions and
limitations under the License.
Utilities for building and looking up Huffman trees.
Utilities for building Huffman decoding tables.
*/
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "./huffman.h"
#include "./safe_malloc.h"
@ -25,231 +26,137 @@
extern "C" {
#endif
#define NON_EXISTENT_SYMBOL (-1)
#define MAX_ALLOWED_CODE_LENGTH 15
#define MAX_LENGTH 15
static void TreeNodeInit(HuffmanTreeNode* const node) {
node->children_ = -1; /* means: 'unassigned so far' */
}
static int NodeIsEmpty(const HuffmanTreeNode* const node) {
return (node->children_ < 0);
}
static int IsFull(const HuffmanTree* const tree) {
return (tree->num_nodes_ == tree->max_nodes_);
}
static void AssignChildren(HuffmanTree* const tree,
HuffmanTreeNode* const node) {
HuffmanTreeNode* const children = tree->root_ + tree->num_nodes_;
node->children_ = (int)(children - node);
assert(children - node == (int)(children - node));
tree->num_nodes_ += 2;
TreeNodeInit(children + 0);
TreeNodeInit(children + 1);
}
static int TreeInit(HuffmanTree* const tree, int num_leaves) {
assert(tree != NULL);
tree->root_ = NULL;
if (num_leaves == 0) return 0;
/* We allocate maximum possible nodes in the tree at once. */
/* Note that a Huffman tree is a full binary tree; and in a full binary */
/* tree with L leaves, the total number of nodes N = 2 * L - 1. */
tree->max_nodes_ = 2 * num_leaves - 1;
assert(tree->max_nodes_ < (1 << 16)); /* limit for the lut_jump_ table */
tree->root_ = (HuffmanTreeNode*)BrotliSafeMalloc((uint64_t)tree->max_nodes_,
sizeof(*tree->root_));
if (tree->root_ == NULL) return 0;
TreeNodeInit(tree->root_); /* Initialize root. */
tree->num_nodes_ = 1;
memset(tree->lut_bits_, 255, sizeof(tree->lut_bits_));
memset(tree->lut_jump_, 0, sizeof(tree->lut_jump_));
return 1;
}
void BrotliHuffmanTreeRelease(HuffmanTree* const tree) {
if (tree != NULL) {
if (tree->root_ != NULL) {
free(tree->root_);
}
tree->root_ = NULL;
tree->max_nodes_ = 0;
tree->num_nodes_ = 0;
/* Returns reverse(reverse(key, len) + 1, len), where reverse(key, len) is the
bit-wise reversal of the len least significant bits of key. */
static BROTLI_INLINE int GetNextKey(int key, int len) {
int step = 1 << (len - 1);
while (key & step) {
step >>= 1;
}
return (key & (step - 1)) + step;
}
/* Utility: converts Huffman code lengths to corresponding Huffman codes. */
/* 'huff_codes' should be pre-allocated. */
/* Returns false in case of error (memory allocation, invalid codes). */
static int HuffmanCodeLengthsToCodes(const uint8_t* const code_lengths,
int code_lengths_size,
int* const huff_codes) {
int symbol;
int code_len;
int code_length_hist[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 };
int curr_code;
int next_codes[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 };
int max_code_length = 0;
/* Stores code in table[0], table[step], table[2*step], ..., table[end] */
/* Assumes that end is an integer multiple of step */
static BROTLI_INLINE void ReplicateValue(HuffmanCode* table,
int step, int end,
HuffmanCode code) {
do {
end -= step;
table[end] = code;
} while (end > 0);
}
assert(code_lengths != NULL);
assert(code_lengths_size > 0);
assert(huff_codes != NULL);
/* Calculate max code length. */
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > max_code_length) {
max_code_length = code_lengths[symbol];
}
/* Returns the table width of the next 2nd level table. count is the histogram
of bit lengths for the remaining symbols, len is the code length of the next
processed symbol */
static BROTLI_INLINE int NextTableBitSize(const int* const count,
int len, int root_bits) {
int left = 1 << (len - root_bits);
while (len < MAX_LENGTH) {
left -= count[len];
if (left <= 0) break;
++len;
left <<= 1;
}
if (max_code_length > MAX_ALLOWED_CODE_LENGTH) return 0;
return len - root_bits;
}
/* Calculate code length histogram. */
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
++code_length_hist[code_lengths[symbol]];
}
code_length_hist[0] = 0;
int BrotliBuildHuffmanTable(HuffmanCode* root_table,
int root_bits,
const uint8_t* const code_lengths,
int code_lengths_size) {
HuffmanCode code; /* current table entry */
HuffmanCode* table; /* next available space in table */
int len; /* current code length */
int symbol; /* symbol index in original or sorted table */
int key; /* reversed prefix code */
int step; /* step size to replicate values in current table */
int low; /* low bits for current root entry */
int mask; /* mask for low bits */
int table_bits; /* key length of current table */
int table_size; /* size of current table */
int total_size; /* sum of root table size and 2nd level table sizes */
int* sorted; /* symbols sorted by code length */
int count[MAX_LENGTH + 1] = { 0 }; /* number of codes of each length */
int offset[MAX_LENGTH + 1]; /* offsets in sorted table for each length */
/* Calculate the initial values of 'next_codes' for each code length. */
/* next_codes[code_len] denotes the code to be assigned to the next symbol */
/* of code length 'code_len'. */
curr_code = 0;
next_codes[0] = -1; /* Unused, as code length = 0 implies */
/* code doesn't exist. */
for (code_len = 1; code_len <= max_code_length; ++code_len) {
curr_code = (curr_code + code_length_hist[code_len - 1]) << 1;
next_codes[code_len] = curr_code;
sorted = (int*)malloc((size_t)code_lengths_size * sizeof(*sorted));
if (sorted == NULL) {
return 0;
}
/* Get symbols. */
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > 0) {
huff_codes[symbol] = next_codes[code_lengths[symbol]]++;
} else {
huff_codes[symbol] = NON_EXISTENT_SYMBOL;
}
/* build histogram of code lengths */
for (symbol = 0; symbol < code_lengths_size; symbol++) {
count[code_lengths[symbol]]++;
}
return 1;
}
static const uint8_t kReverse7[128] = {
0, 64, 32, 96, 16, 80, 48, 112, 8, 72, 40, 104, 24, 88, 56, 120,
4, 68, 36, 100, 20, 84, 52, 116, 12, 76, 44, 108, 28, 92, 60, 124,
2, 66, 34, 98, 18, 82, 50, 114, 10, 74, 42, 106, 26, 90, 58, 122,
6, 70, 38, 102, 22, 86, 54, 118, 14, 78, 46, 110, 30, 94, 62, 126,
1, 65, 33, 97, 17, 81, 49, 113, 9, 73, 41, 105, 25, 89, 57, 121,
5, 69, 37, 101, 21, 85, 53, 117, 13, 77, 45, 109, 29, 93, 61, 125,
3, 67, 35, 99, 19, 83, 51, 115, 11, 75, 43, 107, 27, 91, 59, 123,
7, 71, 39, 103, 23, 87, 55, 119, 15, 79, 47, 111, 31, 95, 63, 127
};
static int ReverseBitsShort(int bits, int num_bits) {
return kReverse7[bits] >> (7 - num_bits);
}
static int TreeAddSymbol(HuffmanTree* const tree,
int symbol, int code, int code_length) {
int step = HUFF_LUT_BITS;
int base_code;
HuffmanTreeNode* node = tree->root_;
const HuffmanTreeNode* const max_node = tree->root_ + tree->max_nodes_;
assert(symbol == (int16_t)symbol);
if (code_length <= HUFF_LUT_BITS) {
int i = 1 << (HUFF_LUT_BITS - code_length);
base_code = ReverseBitsShort(code, code_length);
do {
int idx;
--i;
idx = base_code | (i << code_length);
tree->lut_symbol_[idx] = (int16_t)symbol;
tree->lut_bits_[idx] = (uint8_t)code_length;
} while (i > 0);
} else {
base_code = ReverseBitsShort((code >> (code_length - HUFF_LUT_BITS)),
HUFF_LUT_BITS);
/* generate offsets into sorted symbol table by code length */
offset[1] = 0;
for (len = 1; len < MAX_LENGTH; len++) {
offset[len + 1] = offset[len] + count[len];
}
while (code_length-- > 0) {
if (node >= max_node) {
return 0;
}
if (NodeIsEmpty(node)) {
if (IsFull(tree)) return 0; /* error: too many symbols. */
AssignChildren(tree, node);
} else if (!HuffmanTreeNodeIsNotLeaf(node)) {
return 0; /* leaf is already occupied. */
}
node += node->children_ + ((code >> code_length) & 1);
if (--step == 0) {
tree->lut_jump_[base_code] = (int16_t)(node - tree->root_);
}
}
if (NodeIsEmpty(node)) {
node->children_ = 0; /* turn newly created node into a leaf. */
} else if (HuffmanTreeNodeIsNotLeaf(node)) {
return 0; /* trying to assign a symbol to already used code. */
}
node->symbol_ = symbol; /* Add symbol in this node. */
return 1;
}
int BrotliHuffmanTreeBuildImplicit(HuffmanTree* const tree,
const uint8_t* const code_lengths,
int code_lengths_size) {
int symbol;
int num_symbols = 0;
int root_symbol = 0;
assert(tree != NULL);
assert(code_lengths != NULL);
/* Find out number of symbols and the root symbol. */
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > 0) {
/* Note: code length = 0 indicates non-existent symbol. */
++num_symbols;
root_symbol = symbol;
/* sort symbols by length, by symbol order within each length */
for (symbol = 0; symbol < code_lengths_size; symbol++) {
if (code_lengths[symbol] != 0) {
sorted[offset[code_lengths[symbol]]++] = symbol;
}
}
/* Initialize the tree. Will fail for num_symbols = 0 */
if (!TreeInit(tree, num_symbols)) return 0;
table = root_table;
table_bits = root_bits;
table_size = 1 << table_bits;
total_size = table_size;
/* Build tree. */
if (num_symbols == 1) { /* Trivial case. */
const int max_symbol = code_lengths_size;
if (root_symbol < 0 || root_symbol >= max_symbol) {
BrotliHuffmanTreeRelease(tree);
return 0;
/* special case code with only one value */
if (offset[MAX_LENGTH] == 1) {
code.bits = 0;
code.value = (uint16_t)sorted[0];
for (key = 0; key < total_size; ++key) {
table[key] = code;
}
return TreeAddSymbol(tree, root_symbol, 0, 0);
} else { /* Normal case. */
int ok = 0;
free(sorted);
return total_size;
}
/* Get Huffman codes from the code lengths. */
int* const codes =
(int*)BrotliSafeMalloc((uint64_t)code_lengths_size, sizeof(*codes));
if (codes == NULL) goto End;
if (!HuffmanCodeLengthsToCodes(code_lengths, code_lengths_size, codes)) {
goto End;
/* fill in root table */
key = 0;
symbol = 0;
for (len = 1, step = 2; len <= root_bits; ++len, step <<= 1) {
for (; count[len] > 0; --count[len]) {
code.bits = (uint8_t)(len);
code.value = (uint16_t)sorted[symbol++];
ReplicateValue(&table[key], step, table_size, code);
key = GetNextKey(key, len);
}
}
/* Add symbols one-by-one. */
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > 0) {
if (!TreeAddSymbol(tree, symbol, codes[symbol], code_lengths[symbol])) {
goto End;
}
/* fill in 2nd level tables and add pointers to root table */
mask = total_size - 1;
low = -1;
for (len = root_bits + 1, step = 2; len <= MAX_LENGTH; ++len, step <<= 1) {
for (; count[len] > 0; --count[len]) {
if ((key & mask) != low) {
table += table_size;
table_bits = NextTableBitSize(count, len, root_bits);
table_size = 1 << table_bits;
total_size += table_size;
low = key & mask;
root_table[low].bits = (uint8_t)(table_bits + root_bits);
root_table[low].value = (uint16_t)((table - root_table) - low);
}
code.bits = (uint8_t)(len - root_bits);
code.value = (uint16_t)sorted[symbol++];
ReplicateValue(&table[key >> root_bits], step, table_size, code);
key = GetNextKey(key, len);
}
ok = 1;
End:
free(codes);
ok = ok && IsFull(tree);
if (!ok) BrotliHuffmanTreeRelease(tree);
return ok;
}
free(sorted);
return total_size;
}
#if defined(__cplusplus) || defined(c_plusplus)

49
dec/huffman.h
View File

@ -12,7 +12,7 @@
See the License for the specific language governing permissions and
limitations under the License.
Utilities for building and looking up Huffman trees.
Utilities for building Huffman decoding tables.
*/
#ifndef BROTLI_DEC_HUFFMAN_H_
@ -25,48 +25,17 @@
extern "C" {
#endif
/* A node of a Huffman tree. */
typedef struct {
int symbol_;
int children_; /* delta offset to both children (contiguous) or 0 if leaf. */
} HuffmanTreeNode;
uint8_t bits; /* number of bits used for this symbol */
uint16_t value; /* symbol value or table offset */
} HuffmanCode;
/* Huffman Tree. */
#define HUFF_LUT_BITS 7
#define HUFF_LUT (1U << HUFF_LUT_BITS)
typedef struct HuffmanTree HuffmanTree;
struct HuffmanTree {
/* Fast lookup for short bit lengths. */
uint8_t lut_bits_[HUFF_LUT];
int16_t lut_symbol_[HUFF_LUT];
int16_t lut_jump_[HUFF_LUT];
/* Complete tree for lookups. */
HuffmanTreeNode* root_; /* all the nodes, starting at root. */
int max_nodes_; /* max number of nodes */
int num_nodes_; /* number of currently occupied nodes */
};
/* Returns true if the given node is not a leaf of the Huffman tree. */
static BROTLI_INLINE int HuffmanTreeNodeIsNotLeaf(
const HuffmanTreeNode* const node) {
return node->children_;
}
/* Go down one level. Most critical function. 'right_child' must be 0 or 1. */
static BROTLI_INLINE const HuffmanTreeNode* HuffmanTreeNextNode(
const HuffmanTreeNode* node, int right_child) {
return node + node->children_ + right_child;
}
/* Releases the nodes of the Huffman tree. */
/* Note: It does NOT free 'tree' itself. */
void BrotliHuffmanTreeRelease(HuffmanTree* const tree);
/* Builds Huffman tree assuming code lengths are implicitly in symbol order. */
/* Builds Huffman lookup table assuming code lengths are in symbol order. */
/* Returns false in case of error (invalid tree or memory error). */
int BrotliHuffmanTreeBuildImplicit(HuffmanTree* const tree,
const uint8_t* const code_lengths,
int code_lengths_size);
int BrotliBuildHuffmanTable(HuffmanCode* root_table,
int root_bits,
const uint8_t* const code_lengths,
int code_lengths_size);
#if defined(__cplusplus) || defined(c_plusplus)
} /* extern "C" */

152
enc/backward_references.cc
View File

@ -45,66 +45,97 @@ void CreateBackwardReferences(size_t num_bytes,
average_cost /= num_bytes;
hasher->set_average_cost(average_cost);
// M1 match is for considering for two repeated copies, if moving
// one literal form the previous copy to the current one allows the
// current copy to be more efficient (because the way static dictionary
// codes words). M1 matching improves text compression density by ~0.15 %.
bool match_found_M1 = false;
size_t best_len_M1 = 0;
size_t best_len_code_M1 = 0;
size_t best_dist_M1 = 0;
double best_score_M1 = 0;
while (i + 2 < i_end) {
size_t best_len = 0;
size_t best_len_code = 0;
size_t best_dist = 0;
double best_score = 0;
size_t max_distance = std::min(i + i_diff, max_backward_limit);
bool in_dictionary;
hasher->set_insert_length(insert_length);
bool match_found = hasher->FindLongestMatch(
ringbuffer, literal_cost, ringbuffer_mask,
i + i_diff, i_end - i, max_distance,
&best_len, &best_len_code, &best_dist, &best_score);
&best_len, &best_len_code, &best_dist, &best_score, &in_dictionary);
bool best_in_dictionary = in_dictionary;
if (match_found) {
// Found a match. Let's look for something even better ahead.
int delayed_backward_references_in_row = 0;
while (i + 4 < i_end &&
delayed_backward_references_in_row < 4) {
size_t best_len_2 = 0;
size_t best_len_code_2 = 0;
size_t best_dist_2 = 0;
double best_score_2 = 0;
max_distance = std::min(i + i_diff + 1, max_backward_limit);
if (match_found_M1 && best_score_M1 > best_score) {
// Two copies after each other. Take the last literal from the
// last copy, and use it as the first of this one.
(commands->rbegin())->copy_length_ -= 1;
(commands->rbegin())->copy_length_code_ -= 1;
hasher->Store(ringbuffer + i, i + i_diff);
match_found = hasher->FindLongestMatch(
ringbuffer, literal_cost, ringbuffer_mask,
i + i_diff + 1, i_end - i - 1, max_distance,
&best_len_2, &best_len_code_2, &best_dist_2, &best_score_2);
double cost_diff_lazy = 0;
if (best_len >= 4) {
cost_diff_lazy +=
literal_cost[(i + 4) & ringbuffer_mask] - average_cost;
}
{
const int tail_length = best_len_2 - best_len + 1;
for (int k = 0; k < tail_length; ++k) {
cost_diff_lazy -=
literal_cost[(i + best_len + k) & ringbuffer_mask] -
average_cost;
--i;
best_len = best_len_M1;
best_len_code = best_len_code_M1;
best_dist = best_dist_M1;
best_score = best_score_M1;
// in_dictionary doesn't need to be correct, but it is the only
// reason why M1 matching should be beneficial here. Setting it here
// will only disable further M1 matching against this copy.
best_in_dictionary = true;
in_dictionary = true;
} else {
// Found a match. Let's look for something even better ahead.
int delayed_backward_references_in_row = 0;
while (i + 4 < i_end &&
delayed_backward_references_in_row < 4) {
size_t best_len_2 = 0;
size_t best_len_code_2 = 0;
size_t best_dist_2 = 0;
double best_score_2 = 0;
max_distance = std::min(i + i_diff + 1, max_backward_limit);
hasher->Store(ringbuffer + i, i + i_diff);
match_found = hasher->FindLongestMatch(
ringbuffer, literal_cost, ringbuffer_mask,
i + i_diff + 1, i_end - i - 1, max_distance,
&best_len_2, &best_len_code_2, &best_dist_2, &best_score_2,
&in_dictionary);
double cost_diff_lazy = 0;
if (best_len >= 4) {
cost_diff_lazy +=
literal_cost[(i + 4) & ringbuffer_mask] - average_cost;
}
}
// If we are not inserting any symbols, inserting one is more
// expensive than if we were inserting symbols anyways.
if (insert_length < 1) {
cost_diff_lazy += 0.97;
}
// Add bias to slightly avoid lazy matching.
cost_diff_lazy += 2.0 + delayed_backward_references_in_row * 0.2;
cost_diff_lazy += 0.04 * literal_cost[i & ringbuffer_mask];
{
const int tail_length = best_len_2 - best_len + 1;
for (int k = 0; k < tail_length; ++k) {
cost_diff_lazy -=
literal_cost[(i + best_len + k) & ringbuffer_mask] -
average_cost;
}
}
// If we are not inserting any symbols, inserting one is more
// expensive than if we were inserting symbols anyways.
if (insert_length < 1) {
cost_diff_lazy += 0.97;
}
// Add bias to slightly avoid lazy matching.
cost_diff_lazy += 2.0 + delayed_backward_references_in_row * 0.2;
cost_diff_lazy += 0.04 * literal_cost[i & ringbuffer_mask];
if (match_found && best_score_2 >= best_score + cost_diff_lazy) {
// Ok, let's just write one byte for now and start a match from the
// next byte.
++insert_length;
++delayed_backward_references_in_row;
best_len = best_len_2;
best_len_code = best_len_code_2;
best_dist = best_dist_2;
best_score = best_score_2;
i++;
} else {
break;
if (match_found && best_score_2 >= best_score + cost_diff_lazy) {
// Ok, let's just write one byte for now and start a match from the
// next byte.
++insert_length;
++delayed_backward_references_in_row;
best_len = best_len_2;
best_len_code = best_len_code_2;
best_dist = best_dist_2;
best_score = best_score_2;
best_in_dictionary = in_dictionary;
i++;
} else {
break;
}
}
}
Command cmd;
@ -117,13 +148,40 @@ void CreateBackwardReferences(size_t num_bytes,
insert_length = 0;
++i;
for (int j = 1; j < best_len; ++j) {
// Copy all copied literals to the hasher, except the last one.
// We cannot store the last one yet, otherwise we couldn't find
// the possible M1 match.
for (int j = 1; j < best_len - 1; ++j) {
if (i + 2 < i_end) {
hasher->Store(ringbuffer + i, i + i_diff);
}
++i;
}
// Prepare M1 match.
if (best_len >= 4 && i + 20 < i_end && !best_in_dictionary) {
max_distance = std::min(i + i_diff, max_backward_limit);
match_found_M1 = hasher->FindLongestMatch(
ringbuffer, literal_cost, ringbuffer_mask,
i + i_diff, i_end - i, max_distance,
&best_len_M1, &best_len_code_M1, &best_dist_M1, &best_score_M1,
&in_dictionary);
} else {
match_found_M1 = false;
in_dictionary = false;
}
// This byte is just moved from the previous copy to the current,
// that is no gain.
best_score_M1 -= literal_cost[i & ringbuffer_mask];
// Adjust for losing the opportunity for lazy matching.
best_score_M1 -= 3.75;
// Store the last one of the match.
if (i + 2 < i_end) {
hasher->Store(ringbuffer + i, i + i_diff);
}
++i;
} else {
match_found_M1 = false;
++insert_length;
hasher->Store(ringbuffer + i, i + i_diff);
++i;

2
enc/bit_cost.h
View File

@ -93,7 +93,7 @@ static inline int HuffmanBitCost(const uint8_t* depth, int length) {
cost[17] += 3;
int tree_size = 0;
int bits = 6 + 3 * max_depth; // huffman tree of huffman tree cost
int bits = 6 + 2 * max_depth; // huffman tree of huffman tree cost
for (int i = 0; i < kCodeLengthCodes; ++i) {
bits += histogram[i] * cost[i]; // huffman tree bit cost
tree_size += histogram[i];

6
enc/block_splitter.cc
View File

@ -31,16 +31,16 @@
namespace brotli {
static const int kMaxLiteralHistograms = 48;
static const int kMaxLiteralHistograms = 100;
static const int kMaxCommandHistograms = 50;
static const double kLiteralBlockSwitchCost = 26;
static const double kCommandBlockSwitchCost = 13.5;
static const double kDistanceBlockSwitchCost = 14.6;
static const int kLiteralStrideLength = 70;
static const int kCommandStrideLength = 40;
static const int kSymbolsPerLiteralHistogram = 550;
static const int kSymbolsPerLiteralHistogram = 544;
static const int kSymbolsPerCommandHistogram = 530;
static const int kSymbolsPerDistanceHistogram = 550;
static const int kSymbolsPerDistanceHistogram = 544;
static const int kMinLengthForBlockSplitting = 128;
static const int kIterMulForRefining = 2;
static const int kMinItersForRefining = 100;

189
enc/encode.cc
View File

@ -77,6 +77,68 @@ void EncodeVarLenUint8(int n, int* storage_ix, uint8_t* storage) {
}
}
int ParseAsUTF8(int* symbol, const uint8_t* input, int size) {
// ASCII
if ((input[0] & 0x80) == 0) {
*symbol = input[0];
if (*symbol > 0) {
return 1;
}
}
// 2-byte UTF8
if (size > 1 &&
(input[0] & 0xe0) == 0xc0 &&
(input[1] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x1f) << 6) |
(input[1] & 0x3f));
if (*symbol > 0x7f) {
return 2;
}
}
// 3-byte UFT8
if (size > 2 &&
(input[0] & 0xf0) == 0xe0 &&
(input[1] & 0xc0) == 0x80 &&
(input[2] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x0f) << 12) |
((input[1] & 0x3f) << 6) |
(input[2] & 0x3f));
if (*symbol > 0x7ff) {
return 3;
}
}
// 4-byte UFT8
if (size > 3 &&
(input[0] & 0xf8) == 0xf0 &&
(input[1] & 0xc0) == 0x80 &&
(input[2] & 0xc0) == 0x80 &&
(input[3] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x07) << 18) |
((input[1] & 0x3f) << 12) |
((input[2] & 0x3f) << 6) |
(input[3] & 0x3f));
if (*symbol > 0xffff && *symbol <= 0x10ffff) {
return 4;
}
}
// Not UTF8, emit a special symbol above the UTF8-code space
*symbol = 0x110000 | input[0];
return 1;
}
// Returns true if at least min_fraction of the data is UTF8-encoded.
bool IsMostlyUTF8(const uint8_t* data, size_t length, double min_fraction) {
size_t size_utf8 = 0;
size_t pos = 0;
while (pos < length) {
int symbol;
int bytes_read = ParseAsUTF8(&symbol, data + pos, length - pos);
pos += bytes_read;
if (symbol < 0x110000) size_utf8 += bytes_read;
}
return size_utf8 > min_fraction * length;
}
void EncodeMetaBlockLength(size_t meta_block_size,
bool is_last,
bool is_uncompressed,
@ -118,7 +180,7 @@ void StoreHuffmanTreeOfHuffmanTreeToBitMask(
const uint8_t* code_length_bitdepth,
int* storage_ix, uint8_t* storage) {
static const uint8_t kStorageOrder[kCodeLengthCodes] = {
1, 2, 3, 4, 0, 17, 5, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15,
1, 2, 3, 4, 0, 5, 17, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15,
};
// Throw away trailing zeros:
int codes_to_store = kCodeLengthCodes;
@ -147,7 +209,7 @@ void StoreHuffmanTreeOfHuffmanTreeToBitMask(
WriteBits(2, skip_some, storage_ix, storage);
for (int i = skip_some; i < codes_to_store; ++i) {
uint8_t len[] = { 2, 4, 3, 2, 2, 4 };
uint8_t bits[] = { 0, 5, 1, 3, 2, 13 };
uint8_t bits[] = { 0, 7, 3, 2, 1, 15 };
int v = code_length_bitdepth[kStorageOrder[i]];
WriteBits(len[v], bits[v], storage_ix, storage);
}
@ -175,54 +237,49 @@ void StoreHuffmanTreeToBitMask(
}
template<int kSize>
void StoreHuffmanCode(const EntropyCode<kSize>& code, int alphabet_size,
int* storage_ix, uint8_t* storage) {
void StoreHuffmanCodeSimple(
const EntropyCode<kSize>& code, int alphabet_size,
int max_bits,
int* storage_ix, uint8_t* storage) {
const uint8_t *depth = &code.depth_[0];
int max_bits_counter = alphabet_size - 1;
int max_bits = 0;
while (max_bits_counter) {
max_bits_counter >>= 1;
++max_bits;
int symbols[4];
// Quadratic sort.
int k, j;
for (k = 0; k < code.count_; ++k) {
symbols[k] = code.symbols_[k];
}
if (code.count_ == 0) { // emit minimal tree for empty cases
// bits: small tree marker: 1, count-1: 0, max_bits-sized encoding for 0
WriteBits(4 + max_bits, 0x1, storage_ix, storage);
return;
}
if (code.count_ <= 4) {
int symbols[4];
// Quadratic sort.
int k, j;
for (k = 0; k < code.count_; ++k) {
symbols[k] = code.symbols_[k];
}
for (k = 0; k < code.count_; ++k) {
for (j = k + 1; j < code.count_; ++j) {
if (depth[symbols[j]] < depth[symbols[k]]) {
int t = symbols[k];
symbols[k] = symbols[j];
symbols[j] = t;
}
for (k = 0; k < code.count_; ++k) {
for (j = k + 1; j < code.count_; ++j) {
if (depth[symbols[j]] < depth[symbols[k]]) {
int t = symbols[k];
symbols[k] = symbols[j];
symbols[j] = t;
}
}
// Small tree marker to encode 1-4 symbols.
WriteBits(2, 1, storage_ix, storage);
WriteBits(2, code.count_ - 1, storage_ix, storage);
for (int i = 0; i < code.count_; ++i) {
WriteBits(max_bits, symbols[i], storage_ix, storage);
}
if (code.count_ == 4) {
if (depth[symbols[0]] == 2 &&
depth[symbols[1]] == 2 &&
depth[symbols[2]] == 2 &&
depth[symbols[3]] == 2) {
WriteBits(1, 0, storage_ix, storage);
} else {
WriteBits(1, 1, storage_ix, storage);
}
}
return;
}
// Small tree marker to encode 1-4 symbols.
WriteBits(2, 1, storage_ix, storage);
WriteBits(2, code.count_ - 1, storage_ix, storage);
for (int i = 0; i < code.count_; ++i) {
WriteBits(max_bits, symbols[i], storage_ix, storage);
}
if (code.count_ == 4) {
if (depth[symbols[0]] == 2 &&
depth[symbols[1]] == 2 &&
depth[symbols[2]] == 2 &&
depth[symbols[3]] == 2) {
WriteBits(1, 0, storage_ix, storage);
} else {
WriteBits(1, 1, storage_ix, storage);
}
}
}
template<int kSize>
void StoreHuffmanCodeComplex(
const EntropyCode<kSize>& code, int alphabet_size,
int* storage_ix, uint8_t* storage) {
const uint8_t *depth = &code.depth_[0];
uint8_t huffman_tree[kSize];
uint8_t huffman_tree_extra_bits[kSize];
int huffman_tree_size = 0;
@ -246,6 +303,31 @@ void StoreHuffmanCode(const EntropyCode<kSize>& code, int alphabet_size,
storage_ix, storage);
}
template<int kSize>
void StoreHuffmanCode(const EntropyCode<kSize>& code, int alphabet_size,
int* storage_ix, uint8_t* storage) {
int max_bits_counter = alphabet_size - 1;
int max_bits = 0;
while (max_bits_counter) {
max_bits_counter >>= 1;
++max_bits;
}
if (code.count_ == 0) {
// Emit a minimal tree for empty cases.
// bits: small tree marker: 1, count-1: 0, max_bits-sized encoding for 0
WriteBits(4 + max_bits, 0x1, storage_ix, storage);
} else if (code.count_ <= 4) {
StoreHuffmanCodeSimple(
code, alphabet_size, max_bits,
storage_ix, storage);
} else {
StoreHuffmanCodeComplex(
code, alphabet_size,
storage_ix, storage);
}
}
template<int kSize>
void StoreHuffmanCodes(const std::vector<EntropyCode<kSize> >& codes,
int alphabet_size,
@ -798,12 +880,23 @@ void BrotliCompressor::WriteMetaBlock(const size_t input_size,
const bool is_last,
size_t* encoded_size,
uint8_t* encoded_buffer) {
static const double kMinUTF8Ratio = 0.75;
bool utf8_mode = false;
std::vector<Command> commands;
if (input_size > 0) {
ringbuffer_.Write(input_buffer, input_size);
EstimateBitCostsForLiterals(input_pos_, input_size,
kRingBufferMask, ringbuffer_.start(),
&literal_cost_[0]);
utf8_mode = IsMostlyUTF8(
&ringbuffer_.start()[input_pos_ & kRingBufferMask],
input_size, kMinUTF8Ratio);
if (utf8_mode) {
EstimateBitCostsForLiteralsUTF8(input_pos_, input_size,
kRingBufferMask, ringbuffer_.start(),
&literal_cost_[0]);
} else {
EstimateBitCostsForLiterals(input_pos_, input_size,
kRingBufferMask, ringbuffer_.start(),
&literal_cost_[0]);
}
CreateBackwardReferences(input_size, input_pos_,
ringbuffer_.start(),
&literal_cost_[0],

119
enc/entropy_encode.cc
View File

@ -182,6 +182,12 @@ void WriteHuffmanTreeRepetitions(
++(*tree_size);
--repetitions;
}
if (repetitions == 7) {
tree[*tree_size] = value;
extra_bits[*tree_size] = 0;
++(*tree_size);
--repetitions;
}
if (repetitions < 3) {
for (int i = 0; i < repetitions; ++i) {
tree[*tree_size] = value;
@ -208,6 +214,12 @@ void WriteHuffmanTreeRepetitionsZeros(
uint8_t* tree,
uint8_t* extra_bits,
int* tree_size) {
if (repetitions == 11) {
tree[*tree_size] = 0;
extra_bits[*tree_size] = 0;
++(*tree_size);
--repetitions;
}
if (repetitions < 3) {
for (int i = 0; i < repetitions; ++i) {
tree[*tree_size] = 0;
@ -230,11 +242,6 @@ void WriteHuffmanTreeRepetitionsZeros(
}
// Heuristics for selecting the stride ranges to collapse.
int ValuesShouldBeCollapsedToStrideAverage(int a, int b) {
return abs(a - b) < 4;
}
int OptimizeHuffmanCountsForRle(int length, int* counts) {
int stride;
int limit;
@ -251,6 +258,35 @@ int OptimizeHuffmanCountsForRle(int length, int* counts) {
break;
}
}
{
int nonzeros = 0;
int smallest_nonzero = 1 << 30;
for (i = 0; i < length; ++i) {
if (counts[i] != 0) {
++nonzeros;
if (smallest_nonzero > counts[i]) {
smallest_nonzero = counts[i];
}
}
}
if (nonzeros < 5) {
// Small histogram will model it well.
return 1;
}
int zeros = length - nonzeros;
if (smallest_nonzero < 4) {
if (zeros < 6) {
for (i = 1; i < length - 1; ++i) {
if (counts[i - 1] != 0 && counts[i] == 0 && counts[i + 1] != 0) {
counts[i] = 1;
}
}
}
}
if (nonzeros < 28) {
return 1;
}
}
// 2) Let's mark all population counts that already can be encoded
// with an rle code.
good_for_rle = (uint8_t*)calloc(length, 1);
@ -282,13 +318,15 @@ int OptimizeHuffmanCountsForRle(int length, int* counts) {
}
}
// 3) Let's replace those population counts that lead to more rle codes.
// Math here is in 24.8 fixed point representation.
const int streak_limit = 1240;
stride = 0;
limit = (counts[0] + counts[1] + counts[2]) / 3 + 1;
limit = 256 * (counts[0] + counts[1] + counts[2]) / 3 + 420;
sum = 0;
for (i = 0; i < length + 1; ++i) {
if (i == length || good_for_rle[i] ||
(i != 0 && good_for_rle[i - 1]) ||
!ValuesShouldBeCollapsedToStrideAverage(counts[i], limit)) {
abs(256 * counts[i] - limit) >= streak_limit) {
if (stride >= 4 || (stride >= 3 && sum == 0)) {
int k;
// The stride must end, collapse what we have, if we have enough (4).
@ -311,9 +349,9 @@ int OptimizeHuffmanCountsForRle(int length, int* counts) {
if (i < length - 2) {
// All interesting strides have a count of at least 4,
// at least when non-zeros.
limit = (counts[i] + counts[i + 1] + counts[i + 2]) / 3 + 1;
limit = 256 * (counts[i] + counts[i + 1] + counts[i + 2]) / 3 + 420;
} else if (i < length) {
limit = counts[i];
limit = 256 * counts[i];
} else {
limit = 0;
}
@ -322,7 +360,10 @@ int OptimizeHuffmanCountsForRle(int length, int* counts) {
if (i != length) {
sum += counts[i];
if (stride >= 4) {
limit = (sum + stride / 2) / stride;
limit = (256 * sum + stride / 2) / stride;
}
if (stride == 4) {
limit += 120;
}
}
}
@ -331,16 +372,70 @@ int OptimizeHuffmanCountsForRle(int length, int* counts) {
}
static void DecideOverRleUse(const uint8_t* depth, const int length,
bool *use_rle_for_non_zero,
bool *use_rle_for_zero) {
int total_reps_zero = 0;
int total_reps_non_zero = 0;
int count_reps_zero = 0;
int count_reps_non_zero = 0;
int new_length = length;
for (int i = 0; i < length; ++i) {
if (depth[length - i - 1] == 0) {
--new_length;
} else {
break;
}
}
for (uint32_t i = 0; i < new_length;) {
const int value = depth[i];
int reps = 1;
// Find rle coding for longer codes.
// Shorter codes seem not to benefit from rle.
for (uint32_t k = i + 1; k < new_length && depth[k] == value; ++k) {
++reps;
}
if (reps >= 3 && value == 0) {
total_reps_zero += reps;
++count_reps_zero;
}
if (reps >= 4 && value != 0) {
total_reps_non_zero += reps;
++count_reps_non_zero;
}
i += reps;
}
total_reps_non_zero -= count_reps_non_zero * 2;
total_reps_zero -= count_reps_zero * 2;
*use_rle_for_non_zero = total_reps_non_zero > 2;
*use_rle_for_zero = total_reps_zero > 2;
}
void WriteHuffmanTree(const uint8_t* depth, const int length,
uint8_t* tree,
uint8_t* extra_bits_data,
int* huffman_tree_size) {
int previous_value = 8;
// First gather statistics on if it is a good idea to do rle.
bool use_rle_for_non_zero;
bool use_rle_for_zero;
DecideOverRleUse(depth, length, &use_rle_for_non_zero, &use_rle_for_zero);
// Actual rle coding.
for (uint32_t i = 0; i < length;) {
const int value = depth[i];
int reps = 1;
for (uint32_t k = i + 1; k < length && depth[k] == value; ++k) {
++reps;
if (length > 50) {
// Find rle coding for longer codes.
// Shorter codes seem not to benefit from rle.
if ((value != 0 && use_rle_for_non_zero) ||
(value == 0 && use_rle_for_zero)) {
for (uint32_t k = i + 1; k < length && depth[k] == value; ++k) {
++reps;
}
}
}
if (value == 0) {
WriteHuffmanTreeRepetitionsZeros(reps, tree, extra_bits_data,

2
enc/entropy_encode.h
View File

@ -86,7 +86,7 @@ void BuildEntropyCode(const Histogram<kSize>& histogram,
++code->count_;
}
}
if (code->count_ >= 64) {
if (alphabet_size >= 50 && code->count_ >= 16) {
int counts[kSize];
memcpy(counts, &histogram.data_[0], sizeof(counts[0]) * kSize);
OptimizeHuffmanCountsForRle(alphabet_size, counts);

13
enc/hash.h
View File

@ -150,7 +150,10 @@ class HashLongestMatch {
size_t * __restrict best_len_out,
size_t * __restrict best_len_code_out,
size_t * __restrict best_distance_out,
double * __restrict best_score_out) {
double * __restrict best_score_out,
bool * __restrict in_dictionary) {
*in_dictionary = true;
*best_len_code_out = 0;
const size_t cur_ix_masked = cur_ix & ring_buffer_mask;
const double start_cost4 = literal_cost == NULL ? 20 :
literal_cost[cur_ix_masked] +
@ -166,9 +169,9 @@ class HashLongestMatch {
literal_cost[(cur_ix + 1) & ring_buffer_mask] + 1.2;
bool match_found = false;
// Don't accept a short copy from far away.
double best_score = 8.25;
double best_score = 8.11;
if (insert_length_ < 4) {
double cost_diff[4] = { 0.20, 0.09, 0.05, 0.03 };
double cost_diff[4] = { 0.10, 0.04, 0.02, 0.01 };
best_score += cost_diff[insert_length_];
}
size_t best_len = *best_len_out;
@ -235,6 +238,7 @@ class HashLongestMatch {
*best_distance_out = best_ix;
*best_score_out = best_score;
match_found = true;
*in_dictionary = backward > max_backward;
}
}
}
@ -257,7 +261,7 @@ class HashLongestMatch {
continue;
}
int len = 2;
const double score = start_cost2 - 1.70 * Log2Floor(backward);
const double score = start_cost2 - 2.3 * Log2Floor(backward);
if (best_score < score) {
best_score = score;
@ -309,6 +313,7 @@ class HashLongestMatch {
*best_distance_out = best_ix;
*best_score_out = best_score;
match_found = true;
*in_dictionary = false;
}
}
}

99
enc/literal_cost.cc
View File

@ -22,6 +22,104 @@
namespace brotli {
static int UTF8Position(int last, int c, int clamp) {
if (c < 128) {
return 0; // Next one is the 'Byte 1' again.
} else if (c >= 192) {
return std::min(1, clamp); // Next one is the 'Byte 2' of utf-8 encoding.
} else {
// Let's decide over the last byte if this ends the sequence.
if (last < 0xe0) {
return 0; // Completed two or three byte coding.
} else {
return std::min(2, clamp); // Next one is the 'Byte 3' of utf-8 encoding.
}
}
}
static int DecideMultiByteStatsLevel(size_t pos, size_t len, size_t mask,
const uint8_t *data) {
int counts[3] = { 0 };
int max_utf8 = 1; // should be 2, but 1 compresses better.
int last_c = 0;
int utf8_pos = 0;
for (int i = 0; i < len; ++i) {
int c = data[(pos + i) & mask];
utf8_pos = UTF8Position(last_c, c, 2);
++counts[utf8_pos];
last_c = c;
}
if (counts[2] < 500) {
max_utf8 = 1;
}
if (counts[1] + counts[2] < 25) {
max_utf8 = 0;
}
return max_utf8;
}
void EstimateBitCostsForLiteralsUTF8(size_t pos, size_t len, size_t mask,
const uint8_t *data, float *cost) {
// max_utf8 is 0 (normal ascii single byte modeling),
// 1 (for 2-byte utf-8 modeling), or 2 (for 3-byte utf-8 modeling).
const int max_utf8 = DecideMultiByteStatsLevel(pos, len, mask, data);
int histogram[3][256] = { { 0 } };
int window_half = 495;
int in_window = std::min(static_cast<size_t>(window_half), len);
int in_window_utf8[3] = { 0 };
// Bootstrap histograms.
int last_c = 0;
int utf8_pos = 0;
for (int i = 0; i < in_window; ++i) {
int c = data[(pos + i) & mask];
++histogram[utf8_pos][c];
++in_window_utf8[utf8_pos];
utf8_pos = UTF8Position(last_c, c, max_utf8);
last_c = c;
}
// Compute bit costs with sliding window.
for (int i = 0; i < len; ++i) {
if (i - window_half >= 0) {
// Remove a byte in the past.
int c = (i - window_half - 1) < 0 ?
0 : data[(pos + i - window_half - 1) & mask];
int last_c = (i - window_half - 2) < 0 ?
0 : data[(pos + i - window_half - 2) & mask];
int utf8_pos2 = UTF8Position(last_c, c, max_utf8);
--histogram[utf8_pos2][data[(pos + i - window_half) & mask]];
--in_window_utf8[utf8_pos2];
}
if (i + window_half < len) {
// Add a byte in the future.
int c = (i + window_half - 1) < 0 ?
0 : data[(pos + i + window_half - 1) & mask];
int last_c = (i + window_half - 2) < 0 ?
0 : data[(pos + i + window_half - 2) & mask];
int utf8_pos2 = UTF8Position(last_c, c, max_utf8);
++histogram[utf8_pos2][data[(pos + i + window_half) & mask]];
++in_window_utf8[utf8_pos2];
}
int c = i < 1 ? 0 : data[(pos + i - 1) & mask];
int last_c = i < 2 ? 0 : data[(pos + i - 2) & mask];
int utf8_pos = UTF8Position(last_c, c, max_utf8);
int masked_pos = (pos + i) & mask;
int histo = histogram[utf8_pos][data[masked_pos]];
if (histo == 0) {
histo = 1;
}
cost[masked_pos] = log2(static_cast<double>(in_window_utf8[utf8_pos])
/ histo);
cost[masked_pos] += 0.02905;
if (cost[masked_pos] < 1.0) {
cost[masked_pos] *= 0.5;
cost[masked_pos] += 0.5;
}
}
}
void EstimateBitCostsForLiterals(size_t pos, size_t len, size_t mask,
const uint8_t *data, float *cost) {
int histogram[256] = { 0 };
@ -59,4 +157,5 @@ void EstimateBitCostsForLiterals(size_t pos, size_t len, size_t mask,
}
}
} // namespace brotli

7
enc/literal_cost.h
View File

@ -26,7 +26,12 @@ namespace brotli {
// ringbuffer (data, mask) will take entropy coded and writes these estimates
// to the ringbuffer (cost, mask).
void EstimateBitCostsForLiterals(size_t pos, size_t len, size_t mask,
const uint8_t *data, float *cost);
const uint8_t *data,
float *cost);
void EstimateBitCostsForLiteralsUTF8(size_t pos, size_t len, size_t mask,
const uint8_t *data,
float *cost);
} // namespace brotli