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util/chd.cpp: Calculate size of buffer needed to store hunk map (fixes #12023). (#12040)

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balr0g 2024-02-16 14:46:29 -05:00 committed by GitHub
parent f5c4d82aa7
commit d64e3f7cf2
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1 changed files with 19 additions and 8 deletions
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src/lib/util/chd.cpp
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@ -2031,9 +2031,26 @@ std::error_condition chd_file::compress_v5_map()
}
}
// compute a tree and export it to the buffer
std::vector<uint8_t> compressed(m_hunkcount * 6);
// determine the number of bits we need to hold the a length and a hunk index
const uint8_t lengthbits = bits_for_value(max_complen);
const uint8_t selfbits = bits_for_value(max_self);
const uint8_t parentbits = bits_for_value(max_parent);
// determine the needed size of the output buffer
// 16 bytes is required for the header
// max len per entry given to huffman encoder at instantiation is 8 bits
// this corresponds to worst-case max 12 bits per entry when RLE encoded.
// max additional bits per entry after RLE encoded tree is
// for COMPRESSION_TYPE_0-3: lengthbits+16
// for COMPRESSION_NONE: 16
// for COMPRESSION_SELF: selfbits
// for COMPRESSION_PARENT: parentbits
// the overall size is clamped later with bitbuf.flush()
int nbits_needed = (8*16) + (12 + std::max<int>({lengthbits+16, selfbits, parentbits}))*m_hunkcount;
std::vector<uint8_t> compressed(nbits_needed / 8 + 1);
bitstream_out bitbuf(&compressed[16], compressed.size() - 16);
// compute a tree and export it to the buffer
huffman_error err = encoder.compute_tree_from_histo();
if (err != HUFFERR_NONE)
throw std::error_condition(error::COMPRESSION_ERROR);
@ -2045,12 +2062,6 @@ std::error_condition chd_file::compress_v5_map()
for (uint8_t *src = &compression_rle[0]; src < dest; src++)
encoder.encode_one(bitbuf, *src);
// determine the number of bits we need to hold the a length
// and a hunk index
uint8_t lengthbits = bits_for_value(max_complen);
uint8_t selfbits = bits_for_value(max_self);
uint8_t parentbits = bits_for_value(max_parent);
// for each compression type, output the relevant data
lastcomp = 0;
count = 0;