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Merge pull request #2 from szabadka/decoder

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Fix BrotliDecompressedSize() to work for an uncompressed plus an empty meta-block.
This commit is contained in:
szabadka 2014-10-27 17:36:07 +01:00
commit c62fa2116f
2 changed files with 55 additions and 14 deletions
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66
dec/decode.c
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@ -633,22 +633,62 @@ int CopyUncompressedBlockToOutput(BrotliOutput output, int len, int pos,
int BrotliDecompressedSize(size_t encoded_size, int BrotliDecompressedSize(size_t encoded_size,
const uint8_t* encoded_buffer, const uint8_t* encoded_buffer,
size_t* decoded_size) { size_t* decoded_size) {
BrotliMemInput memin; int i;
BrotliInput input = BrotliInitMemInput(encoded_buffer, encoded_size, &memin); uint64_t val = 0;
BrotliBitReader br; int bit_pos = 0;
int meta_block_len; int is_last;
int input_end; int is_uncompressed = 0;
int is_uncompressed; int size_nibbles;
if (!BrotliInitBitReader(&br, input)) { int meta_block_len = 0;
if (encoded_size == 0) {
return 0; return 0;
} }
DecodeWindowBits(&br); /* Look at the first 8 bytes, it is enough to decode the length of the first
DecodeMetaBlockLength(&br, &meta_block_len, &input_end, &is_uncompressed); meta-block. */
if (!input_end) { for (i = 0; i < encoded_size && i < 8; ++i) {
return 0; val |= (uint64_t)encoded_buffer[i] << (8 * i);
} }
*decoded_size = (size_t)meta_block_len; /* Skip the window bits. */
return 1; bit_pos += (val & 1) ? 4 : 1;
/* Decode the ISLAST bit. */
is_last = (val >> bit_pos) & 1;
++bit_pos;
if (is_last) {
/* Decode the ISEMPTY bit, if it is set to 1, we are done. */
if ((val >> bit_pos) & 1) {
*decoded_size = 0;
return 1;
}
++bit_pos;
}
/* Decode the length of the first meta-block. */
size_nibbles = (int)((val >> bit_pos) & 3) + 4;
bit_pos += 2;
for (i = 0; i < size_nibbles; ++i) {
meta_block_len |= (int)((val >> bit_pos) & 0xf) << (4 * i);
bit_pos += 4;
}
++meta_block_len;
if (is_last) {
/* If this meta-block is the only one, we are done. */
*decoded_size = (size_t)meta_block_len;
return 1;
}
is_uncompressed = (val >> bit_pos) & 1;
++bit_pos;
if (is_uncompressed) {
/* If the first meta-block is uncompressed, we skip it and look at the
first two bits (ISLAST and ISEMPTY) of the next meta-block, and if
both are set to 1, we have a stream with an uncompressed meta-block
followed by an empty one, so the decompressed size is the size of the
first meta-block. */
int offset = ((bit_pos + 7) >> 3) + meta_block_len;
if (offset < encoded_size && ((encoded_buffer[offset] & 3) == 3)) {
*decoded_size = (size_t)meta_block_len;
return 1;
}
}
return 0;
} }
int BrotliDecompressBuffer(size_t encoded_size, int BrotliDecompressBuffer(size_t encoded_size,

3
dec/decode.h
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@ -27,7 +27,8 @@ extern "C" {
/* Sets *decoded_size to the decompressed size of the given encoded stream. */ /* 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, */ /* This function only works if the encoded buffer has a single meta block, */
/* and this meta block must have the "is last" bit set. */ /* or if it has two meta-blocks, where the first is uncompressed and the */
/* second is empty. */
/* Returns 1 on success, 0 on failure. */ /* Returns 1 on success, 0 on failure. */
int BrotliDecompressedSize(size_t encoded_size, int BrotliDecompressedSize(size_t encoded_size,
const uint8_t* encoded_buffer, const uint8_t* encoded_buffer,