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Fix sumToHash to use hash space more efficiently

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This commit is contained in:
Stella Lau 2017-07-12 10:53:19 -07:00
parent e0d4162464
commit 3a48ffd4fd
1 changed files with 44 additions and 8 deletions
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52
contrib/long_distance_matching/ldm.c
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@ -7,9 +7,9 @@
#include "ldm.h"
#include "util.h"
#define HASH_EVERY 1
#define HASH_EVERY 7
#define LDM_MEMORY_USAGE 22
#define LDM_MEMORY_USAGE 18
#define LDM_HASHLOG (LDM_MEMORY_USAGE-2)
#define LDM_HASHTABLESIZE (1 << (LDM_MEMORY_USAGE))
#define LDM_HASHTABLESIZE_U32 ((LDM_HASHTABLESIZE) >> 2)
@ -132,7 +132,7 @@ static int LDM_isValidMatch(const BYTE *p, const BYTE *match) {
curMatch += 8;
}
if (lengthLeft > 0) {
return LDM_read32(curP) == LDM_read32(curMatch);
return (LDM_read32(curP) == LDM_read32(curMatch));
}
return 1;
}
@ -144,8 +144,15 @@ static int LDM_isValidMatch(const BYTE *p, const BYTE *match) {
* Convert a sum computed from LDM_getRollingHash to a hash value in the range
* of the hash table.
*/
#define LDM_SUM2HASH2(s1,s2) (((s1) + (s2)) & 0xFFFF)
#define LDM_SUM2HASH(sum) (LDM_SUM2HASH2((sum)&0xFFFF,(sum)>>16))
static hash_t LDM_sumToHash(U32 sum) {
return sum & (LDM_HASH_SIZE_U32 - 1);
// return sum & (LDM_HASH_SIZE_U32 - 1);
// return sum % (LDM_HASHTABLESIZE_U32 );
return ((sum* 2654435761U) >> ((32)-LDM_HASHLOG));
// return LDM_SUM2HASH2(sum&0xFFFF, sum >> 16);
}
static U32 LDM_getRollingHash(const char *data, U32 len) {
@ -240,15 +247,32 @@ static void LDM_putHashOfCurrentPositionFromHash(
}
*/
#ifdef COMPUTE_STATS
if (cctx->stats.numHashInserts < LDM_HASHTABLESIZE_U32) {
if (cctx->stats.numHashInserts < LDM_HASHTABLESIZE_U32 ) {
offset_t offset = (cctx->hashTable)[hash].offset;
cctx->stats.numHashInserts++;
if (offset == 0 && !LDM_isValidMatch(cctx->ip, offset + cctx->ibase)) {
if (offset != 0 && !LDM_isValidMatch(cctx->ip, offset + cctx->ibase)) {
// printf("%u %u %zu\n", hash, offset, cctx->ip - cctx->ibase);
// printf("TST: %u %u\n", LDM_read32(cctx->ip), LDM_read32(offset + cctx->ibase));
cctx->stats.numCollisions++;
}
}
#endif
(cctx->hashTable)[hash] = (LDM_hashEntry){ (hash_t)(cctx->ip - cctx->ibase) };
if (((cctx->ip - cctx->ibase) & HASH_EVERY) == HASH_EVERY) {
#ifdef COMPUTE_STATS
/*
offset_t offset = (cctx->hashTable)[hash].offset;
if (offset == 0) {
printf("NEW HASH: %u\n", hash);
}
*/
#endif
(cctx->hashTable)[hash] = (LDM_hashEntry){ (offset_t)(cctx->ip - cctx->ibase) };
}
// Book-keeping
cctx->lastPosHashed = cctx->ip;
cctx->lastHash = hash;
cctx->lastSum = sum;
@ -296,7 +320,8 @@ static void LDM_putHashOfCurrentPositionFromHash(
if (cctx->stats.numHashInserts < LDM_HASHTABLESIZE_U32) {
offset_t offset = (cctx->hashTable)[hash].offset;
cctx->stats.numHashInserts++;
if (offset == 0 && !LDM_isValidMatch(cctx->ip, offset + cctx->ibase)) {
if (offset != 0 && !LDM_isValidMatch(cctx->ip, offset + cctx->ibase)) {
cctx->stats.numCollisions++;
}
}
@ -629,6 +654,17 @@ _last_literals:
cctx.op += lastRun;
}
LDM_printCompressStats(&cctx.stats);
{
U32 tmp = 0;
U32 ctr = 0;
for (; tmp < LDM_HASH_SIZE_U32; tmp++) {
if ((cctx.hashTable)[tmp].offset == 0) {
ctr++;
}
}
printf("HASH: %u %u\n", ctr, LDM_HASH_SIZE_U32);
}
return (cctx.op - (const BYTE *)cctx.obase);
}