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Add crc32_combine_gen() and crc32_combine_op() for fast combines. 

When the same len2 is used repeatedly, it is faster to use
crc32_combine_gen() to generate an operator, that is then used to
combine CRCs with crc32_combine_op().
This commit is contained in:
Mark Adler 2018-11-04 10:31:46 -08:00
parent 47cb412957
commit 41d86c73b2
2 changed files with 97 additions and 0 deletions
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75
crc32.c
View File

@ -50,6 +50,7 @@
#define GF2_DIM 32 /* dimension of GF(2) vectors (length of CRC) */
local z_crc_t gf2_matrix_times OF((const z_crc_t *mat, z_crc_t vec));
local uLong crc32_combine_ OF((uLong crc1, uLong crc2, z_off64_t len2));
local void crc32_combine_gen_ OF((z_crc_t *op, z_off64_t len2));
/* ========================================================================= */
local z_crc_t gf2_matrix_times(mat, vec)
@ -452,3 +453,77 @@ uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
{
return crc32_combine_(crc1, crc2, len2);
}
/* ========================================================================= */
local void crc32_combine_gen_(op, len2)
z_crc_t *op;
z_off64_t len2;
{
z_crc_t row;
int j;
unsigned i;
#ifdef DYNAMIC_CRC_TABLE
if (crc_table_empty)
make_crc_table();
#endif /* DYNAMIC_CRC_TABLE */
/* if len2 is zero or negative, return the identity matrix */
if (len2 <= 0) {
row = 1;
for (j = 0; j < GF2_DIM; j++) {
op[j] = row;
row <<= 1;
}
return;
}
/* at least one bit in len2 is set -- find it, and copy the operator
corresponding to that position into op */
i = 0;
for (;;) {
if (len2 & 1) {
for (j = 0; j < GF2_DIM; j++)
op[j] = crc_comb[i][j];
break;
}
len2 >>= 1;
i = (i + 1) % GF2_DIM;
}
/* for each remaining bit set in len2 (if any), multiply op by the operator
corresponding to that position */
for (;;) {
len2 >>= 1;
i = (i + 1) % GF2_DIM;
if (len2 == 0)
break;
if (len2 & 1)
for (j = 0; j < GF2_DIM; j++)
op[j] = gf2_matrix_times(crc_comb[i], op[j]);
}
}
/* ========================================================================= */
void ZEXPORT crc32_combine_gen(op, len2)
z_crc_t *op;
z_off_t len2;
{
crc32_combine_gen_(op, len2);
}
void ZEXPORT crc32_combine_gen64(op, len2)
z_crc_t *op;
z_off64_t len2;
{
crc32_combine_gen_(op, len2);
}
/* ========================================================================= */
uLong crc32_combine_op(crc1, crc2, op)
uLong crc1;
uLong crc2;
const z_crc_t *op;
{
return gf2_matrix_times(op, crc1) ^ crc2;
}

22
zlib.h
View File

@ -1757,6 +1757,22 @@ ZEXTERN uLong ZEXPORT crc32_combine OF((uLong crc1, uLong crc2, z_off_t len2));
len2.
*/
/*
ZEXTERN void ZEXPORT crc32_combine_gen OF((z_crc_t op[32], z_off_t len2));
Generate the operator op corresponding to length len2, to be used with
crc32_combine_op(). op must have room for 32 z_crc_t values. (32 is the
number of bits in the CRC.)
*/
ZEXTERN uLong ZEXPORT crc32_combine_op OF((uLong crc1, uLong crc2,
const z_crc_t *op));
/*
Give the same result as crc32_combine(), using op in place of len2. op is
is generated from len2 by crc32_combine_gen(). This will be faster than
crc32_combine() if the generated op is used many times.
*/
/* various hacks, don't look :) */
@ -1844,6 +1860,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file)); /* backward compatibility */
ZEXTERN z_off64_t ZEXPORT gzoffset64 OF((gzFile));
ZEXTERN uLong ZEXPORT adler32_combine64 OF((uLong, uLong, z_off64_t));
ZEXTERN uLong ZEXPORT crc32_combine64 OF((uLong, uLong, z_off64_t));
ZEXTERN void ZEXPORT crc32_combine_gen64 OF((z_crc_t *op, z_off64_t));
#endif
#if !defined(ZLIB_INTERNAL) && defined(Z_WANT64)
@ -1854,6 +1871,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file)); /* backward compatibility */
# define z_gzoffset z_gzoffset64
# define z_adler32_combine z_adler32_combine64
# define z_crc32_combine z_crc32_combine64
# define z_crc32_combine_gen z_crc32_combine64_gen
# else
# define gzopen gzopen64
# define gzseek gzseek64
@ -1861,6 +1879,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file)); /* backward compatibility */
# define gzoffset gzoffset64
# define adler32_combine adler32_combine64
# define crc32_combine crc32_combine64
# define crc32_combine_gen crc32_combine_gen64
# endif
# ifndef Z_LARGE64
ZEXTERN gzFile ZEXPORT gzopen64 OF((const char *, const char *));
@ -1869,6 +1888,7 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file)); /* backward compatibility */
ZEXTERN z_off_t ZEXPORT gzoffset64 OF((gzFile));
ZEXTERN uLong ZEXPORT adler32_combine64 OF((uLong, uLong, z_off_t));
ZEXTERN uLong ZEXPORT crc32_combine64 OF((uLong, uLong, z_off_t));
ZEXTERN void ZEXPORT crc32_combine_gen64 OF((z_crc_t *op, z_off_t));
# endif
#else
ZEXTERN gzFile ZEXPORT gzopen OF((const char *, const char *));
@ -1877,12 +1897,14 @@ ZEXTERN int ZEXPORT gzgetc_ OF((gzFile file)); /* backward compatibility */
ZEXTERN z_off_t ZEXPORT gzoffset OF((gzFile));
ZEXTERN uLong ZEXPORT adler32_combine OF((uLong, uLong, z_off_t));
ZEXTERN uLong ZEXPORT crc32_combine OF((uLong, uLong, z_off_t));
ZEXTERN void ZEXPORT crc32_combine_gen OF((z_crc_t *op, z_off_t));
#endif
#else /* Z_SOLO */
ZEXTERN uLong ZEXPORT adler32_combine OF((uLong, uLong, z_off_t));
ZEXTERN uLong ZEXPORT crc32_combine OF((uLong, uLong, z_off_t));
ZEXTERN void ZEXPORT crc32_combine_gen OF((z_crc_t *op, z_off_t));
#endif /* !Z_SOLO */