diff options
Diffstat (limited to 'contrib/xz/src/liblzma/lzma/fastpos.h')
| -rw-r--r-- | contrib/xz/src/liblzma/lzma/fastpos.h | 55 |
1 files changed, 28 insertions, 27 deletions
diff --git a/contrib/xz/src/liblzma/lzma/fastpos.h b/contrib/xz/src/liblzma/lzma/fastpos.h index 4aea231..a3feea5 100644 --- a/contrib/xz/src/liblzma/lzma/fastpos.h +++ b/contrib/xz/src/liblzma/lzma/fastpos.h @@ -14,15 +14,15 @@ #ifndef LZMA_FASTPOS_H #define LZMA_FASTPOS_H -// LZMA encodes match distances (positions) by storing the highest two -// bits using a six-bit value [0, 63], and then the missing lower bits. -// Dictionary size is also stored using this encoding in the new .lzma +// LZMA encodes match distances by storing the highest two bits using +// a six-bit value [0, 63], and then the missing lower bits. +// Dictionary size is also stored using this encoding in the .xz // file format header. // // fastpos.h provides a way to quickly find out the correct six-bit // values. The following table gives some examples of this encoding: // -// pos return +// dist return // 0 0 // 1 1 // 2 2 @@ -48,10 +48,10 @@ // Provided functions or macros // ---------------------------- // -// get_pos_slot(pos) is the basic version. get_pos_slot_2(pos) -// assumes that pos >= FULL_DISTANCES, thus the result is at least -// FULL_DISTANCES_BITS * 2. Using get_pos_slot(pos) instead of -// get_pos_slot_2(pos) would give the same result, but get_pos_slot_2(pos) +// get_dist_slot(dist) is the basic version. get_dist_slot_2(dist) +// assumes that dist >= FULL_DISTANCES, thus the result is at least +// FULL_DISTANCES_BITS * 2. Using get_dist_slot(dist) instead of +// get_dist_slot_2(dist) would give the same result, but get_dist_slot_2(dist) // should be tiny bit faster due to the assumption being made. // // @@ -76,13 +76,14 @@ // slightly faster, but sometimes it is a lot slower. #ifdef HAVE_SMALL -# define get_pos_slot(pos) ((pos) <= 4 ? (pos) : get_pos_slot_2(pos)) +# define get_dist_slot(dist) \ + ((dist) <= 4 ? (dist) : get_dist_slot_2(dist)) static inline uint32_t -get_pos_slot_2(uint32_t pos) +get_dist_slot_2(uint32_t dist) { - const uint32_t i = bsr32(pos); - return (i + i) + ((pos >> (i - 1)) & 1); + const uint32_t i = bsr32(dist); + return (i + i) + ((dist >> (i - 1)) & 1); } @@ -99,39 +100,39 @@ extern const uint8_t lzma_fastpos[1 << FASTPOS_BITS]; #define fastpos_limit(extra, n) \ (UINT32_C(1) << (FASTPOS_BITS + fastpos_shift(extra, n))) -#define fastpos_result(pos, extra, n) \ - lzma_fastpos[(pos) >> fastpos_shift(extra, n)] \ +#define fastpos_result(dist, extra, n) \ + lzma_fastpos[(dist) >> fastpos_shift(extra, n)] \ + 2 * fastpos_shift(extra, n) static inline uint32_t -get_pos_slot(uint32_t pos) +get_dist_slot(uint32_t dist) { // If it is small enough, we can pick the result directly from // the precalculated table. - if (pos < fastpos_limit(0, 0)) - return lzma_fastpos[pos]; + if (dist < fastpos_limit(0, 0)) + return lzma_fastpos[dist]; - if (pos < fastpos_limit(0, 1)) - return fastpos_result(pos, 0, 1); + if (dist < fastpos_limit(0, 1)) + return fastpos_result(dist, 0, 1); - return fastpos_result(pos, 0, 2); + return fastpos_result(dist, 0, 2); } #ifdef FULL_DISTANCES_BITS static inline uint32_t -get_pos_slot_2(uint32_t pos) +get_dist_slot_2(uint32_t dist) { - assert(pos >= FULL_DISTANCES); + assert(dist >= FULL_DISTANCES); - if (pos < fastpos_limit(FULL_DISTANCES_BITS - 1, 0)) - return fastpos_result(pos, FULL_DISTANCES_BITS - 1, 0); + if (dist < fastpos_limit(FULL_DISTANCES_BITS - 1, 0)) + return fastpos_result(dist, FULL_DISTANCES_BITS - 1, 0); - if (pos < fastpos_limit(FULL_DISTANCES_BITS - 1, 1)) - return fastpos_result(pos, FULL_DISTANCES_BITS - 1, 1); + if (dist < fastpos_limit(FULL_DISTANCES_BITS - 1, 1)) + return fastpos_result(dist, FULL_DISTANCES_BITS - 1, 1); - return fastpos_result(pos, FULL_DISTANCES_BITS - 1, 2); + return fastpos_result(dist, FULL_DISTANCES_BITS - 1, 2); } #endif |
