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Add autodocs to internal compressor functions

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emmanuel-marty 2019-04-02 15:03:21 +02:00
parent fa1ef05a31
commit fcfdbe9745
1 changed files with 88 additions and 1 deletions
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89
src/shrink.c
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@ -118,6 +118,15 @@ void lzsa_compressor_destroy(lsza_compressor *pCompressor) {
}
}
/**
* Parse input data, build suffix array and overlaid data structures to speed up match finding
*
* @param pCompressor compression context
* @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
* @param nInWindowSize total input size in bytes (previously compressed bytes + bytes to compress)
*
* @return 0 for success, non-zero for failure
*/
static int lzsa_build_suffix_array(lsza_compressor *pCompressor, const unsigned char *pInWindow, const int nInWindowSize) {
int *intervals = pCompressor->intervals;
@ -147,7 +156,9 @@ static int lzsa_build_suffix_array(lsza_compressor *pCompressor, const unsigned
nCurLen--;
}
/* Rotate permuted LCP into the LCP. This has better cache locality than the direct Kasai LCP method */
/* Rotate permuted LCP into the LCP. This has better cache locality than the direct Kasai LCP method. This also
* saves us from having to build the inverse suffix array index, as the LCP is calculated without it using this method,
* and the interval builder below doesn't need it either. */
intervals[0] &= POS_MASK;
for (i = 1; i < nInWindowSize; i++) {
int nIndex = intervals[i] & POS_MASK;
@ -228,6 +239,16 @@ static int lzsa_build_suffix_array(lsza_compressor *pCompressor, const unsigned
return 0;
}
/**
* Find matches at the specified offset in the input window
*
* @param pCompressor compression context
* @param nOffset offset to find matches at, in the input window
* @param pMatches pointer to returned matches
* @param nMaxMatches maximum number of matches to return (0 for none)
*
* @return number of matches
*/
static int lzsa_find_matches_at(lsza_compressor *pCompressor, const int nOffset, lzsa_match *pMatches, const int nMaxMatches) {
int *intervals = pCompressor->intervals;
int *pos_data = pCompressor->pos_data;
@ -299,15 +320,32 @@ static int lzsa_find_matches_at(lsza_compressor *pCompressor, const int nOffset,
return (int)(matchptr - pMatches);
}
/**
* Skip previously compressed bytes
*
* @param pCompressor compression context
* @param nStartOffset current offset in input window (typically 0)
* @param nEndOffset offset to skip to in input window (typically the number of previously compressed bytes)
*/
static void lzsa_skip_matches(lsza_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
lzsa_match match;
int i;
/* Skipping still requires scanning for matches, as this also performs a lazy update of the intervals. However,
* we don't store the matches. */
for (i = nStartOffset; i < nEndOffset; i++) {
lzsa_find_matches_at(pCompressor, i, &match, 0);
}
}
/**
* Find all matches for the data to be compressed. Up to NMATCHES_PER_OFFSET matches are stored for each offset, for
* the optimizer to look at.
*
* @param pCompressor compression context
* @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
* @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
*/
static void lzsa_find_all_matches(lsza_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
lzsa_match *pMatch = pCompressor->match + (nStartOffset << MATCHES_PER_OFFSET_SHIFT);
int i;
@ -335,6 +373,13 @@ static void lzsa_find_all_matches(lsza_compressor *pCompressor, const int nStart
}
}
/**
* Get the number of extra bytes required to represent a literals length
*
* @param nLength literals length
*
* @return number of extra bytes required
*/
static inline int lzsa_get_literals_varlen_size(const int nLength) {
if (nLength < LITERALS_RUN_LEN) {
return 0;
@ -351,6 +396,14 @@ static inline int lzsa_get_literals_varlen_size(const int nLength) {
}
}
/**
* Write extra literals length bytes to output (compressed) buffer. The caller must first check that there is enough
* room to write the bytes.
*
* @param pOutData pointer to output buffer
* @param nOutOffset current write index into output buffer
* @param nLength literals length
*/
static inline int lzsa_write_literals_varlen(unsigned char *pOutData, int nOutOffset, int nLength) {
if (nLength >= LITERALS_RUN_LEN) {
nLength -= LITERALS_RUN_LEN;
@ -373,6 +426,13 @@ static inline int lzsa_write_literals_varlen(unsigned char *pOutData, int nOutOf
return nOutOffset;
}
/**
* Get the number of extra bytes required to represent an encoded match length
*
* @param nLength encoded match length (actual match length - MIN_MATCH_SIZE)
*
* @return number of extra bytes required
*/
static inline int lzsa_get_match_varlen_size(const int nLength) {
if (nLength < MATCH_RUN_LEN) {
return 0;
@ -389,6 +449,14 @@ static inline int lzsa_get_match_varlen_size(const int nLength) {
}
}
/**
* Write extra encoded match length bytes to output (compressed) buffer. The caller must first check that there is enough
* room to write the bytes.
*
* @param pOutData pointer to output buffer
* @param nOutOffset current write index into output buffer
* @param nLength encoded match length (actual match length - MIN_MATCH_SIZE)
*/
static inline int lzsa_write_match_varlen(unsigned char *pOutData, int nOutOffset, int nLength) {
if (nLength >= MATCH_RUN_LEN) {
nLength -= MATCH_RUN_LEN;
@ -411,6 +479,13 @@ static inline int lzsa_write_match_varlen(unsigned char *pOutData, int nOutOffse
return nOutOffset;
}
/**
* Attempt to pick optimal matches, so as to produce the smallest possible output that decompresses to the same input
*
* @param pCompressor compression context
* @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
* @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
*/
static void lzsa_optimize_matches(lsza_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
int *cost = pCompressor->pos_data; /* Reuse */
int nLastLiteralsOffset;
@ -483,6 +558,18 @@ static void lzsa_optimize_matches(lsza_compressor *pCompressor, const int nStart
}
}
/**
* Emit block of compressed data
*
* @param pCompressor compression context
* @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
* @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
* @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
* @param pOutData pointer to output buffer
* @param nMaxOutDataSize maximum size of output buffer, in bytes
*
* @return size of compressed data in output buffer, or -1 if the data is uncompressible
*/
static int lzsa_write_block(lsza_compressor *pCompressor, const unsigned char *pInWindow, const int nStartOffset, const int nEndOffset, unsigned char *pOutData, const int nMaxOutDataSize) {
int i;
int nNumLiterals = 0;