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Speed up Adler-32 by unrolling loop

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This commit is contained in:
Eric Biggers 2015-01-21 23:53:42 -06:00
parent d46e893a0d
commit fed4597943
1 changed files with 47 additions and 7 deletions
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54
src/adler32.c
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@ -35,22 +35,62 @@
*/ */
#define MAX_BYTES_PER_CHUNK 5552 #define MAX_BYTES_PER_CHUNK 5552
/* Number of bytes to process per loop iteration */
#define UNROLL_FACTOR 4
u32 u32
adler32(const u8 *buffer, size_t size) adler32(const u8 *buffer, size_t size)
{ {
u32 s1 = 1; u32 s1 = 1;
u32 s2 = 0; u32 s2 = 0;
const u8 *p = buffer; const u8 *p = buffer;
const u8 * const end = p + size; const u8 *end = p + size;
while (p != end) { while (p != end) {
const u8 *chunk_end = p + min(end - p, size_t chunk_size = min(end - p, MAX_BYTES_PER_CHUNK);
MAX_BYTES_PER_CHUNK); const u8 *chunk_end = p + chunk_size;
do {
#if UNROLL_FACTOR > 1
size_t num_unrolled_iterations = chunk_size / UNROLL_FACTOR;
while (num_unrolled_iterations--) {
s1 += *p++; s1 += *p++;
s2 += s1; s2 += s1;
} while (p != chunk_end); #if UNROLL_FACTOR >= 2
s1 %= 65521; s1 += *p++;
s2 %= 65521; s2 += s1;
#endif
#if UNROLL_FACTOR >= 3
s1 += *p++;
s2 += s1;
#endif
#if UNROLL_FACTOR >= 4
s1 += *p++;
s2 += s1;
#endif
#if UNROLL_FACTOR >= 5
s1 += *p++;
s2 += s1;
#endif
#if UNROLL_FACTOR >= 6
s1 += *p++;
s2 += s1;
#endif
#if UNROLL_FACTOR >= 7
s1 += *p++;
s2 += s1;
#endif
#if UNROLL_FACTOR >= 8
s1 += *p++;
s2 += s1;
#endif
BUILD_BUG_ON(UNROLL_FACTOR > 8);
}
#endif /* UNROLL_FACTOR > 1 */
while (p != chunk_end) {
s1 += *p++;
s2 += s1;
}
s1 %= DIVISOR;
s2 %= DIVISOR;
} }
return (s2 << 16) | s1; return (s2 << 16) | s1;
} }