ddidderr/zstd-rs
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[lib] Add rsyncable mode

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- Add rsyncable mode to multithreaded mode
- Factor out LDM's hash function for reuse
This commit is contained in:
Nick Terrell
2018-11-14 16:59:57 -08:00
parent c584e84e68
commit b9693d3a49
7 changed files with 218 additions and 80 deletions
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lib/compress/zstd_ldm.c
+7 -57
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@@ -143,56 +143,6 @@ static void ZSTD_ldm_makeEntryAndInsertByTag(ldmState_t* ldmState,
}
}
/** ZSTD_ldm_getRollingHash() :
* Get a 64-bit hash using the first len bytes from buf.
*
* Giving bytes s = s_1, s_2, ... s_k, the hash is defined to be
* H(s) = s_1*(a^(k-1)) + s_2*(a^(k-2)) + ... + s_k*(a^0)
*
* where the constant a is defined to be prime8bytes.
*
* The implementation adds an offset to each byte, so
* H(s) = (s_1 + HASH_CHAR_OFFSET)*(a^(k-1)) + ... */
static U64 ZSTD_ldm_getRollingHash(const BYTE* buf, U32 len)
{
U64 ret = 0;
U32 i;
for (i = 0; i < len; i++) {
ret *= prime8bytes;
ret += buf[i] + LDM_HASH_CHAR_OFFSET;
}
return ret;
}
/** ZSTD_ldm_ipow() :
* Return base^exp. */
static U64 ZSTD_ldm_ipow(U64 base, U64 exp)
{
U64 ret = 1;
while (exp) {
if (exp & 1) { ret *= base; }
exp >>= 1;
base *= base;
}
return ret;
}
U64 ZSTD_ldm_getHashPower(U32 minMatchLength) {
DEBUGLOG(4, "ZSTD_ldm_getHashPower: mml=%u", minMatchLength);
assert(minMatchLength >= ZSTD_LDM_MINMATCH_MIN);
return ZSTD_ldm_ipow(prime8bytes, minMatchLength - 1);
}
/** ZSTD_ldm_updateHash() :
* Updates hash by removing toRemove and adding toAdd. */
static U64 ZSTD_ldm_updateHash(U64 hash, BYTE toRemove, BYTE toAdd, U64 hashPower)
{
hash -= ((toRemove + LDM_HASH_CHAR_OFFSET) * hashPower);
hash *= prime8bytes;
hash += toAdd + LDM_HASH_CHAR_OFFSET;
return hash;
}
/** ZSTD_ldm_countBackwardsMatch() :
* Returns the number of bytes that match backwards before pIn and pMatch.
*
@@ -261,9 +211,9 @@ static U64 ZSTD_ldm_fillLdmHashTable(ldmState_t* state,
const BYTE* cur = lastHashed + 1;
while (cur < iend) {
rollingHash = ZSTD_ldm_updateHash(rollingHash, cur[-1],
cur[ldmParams.minMatchLength-1],
state->hashPower);
rollingHash = ZSTD_rollingHash_rotate(rollingHash, cur[-1],
cur[ldmParams.minMatchLength-1],
state->hashPower);
ZSTD_ldm_makeEntryAndInsertByTag(state,
rollingHash, hBits,
(U32)(cur - base), ldmParams);
@@ -324,11 +274,11 @@ static size_t ZSTD_ldm_generateSequences_internal(
size_t forwardMatchLength = 0, backwardMatchLength = 0;
ldmEntry_t* bestEntry = NULL;
if (ip != istart) {
rollingHash = ZSTD_ldm_updateHash(rollingHash, lastHashed[0],
lastHashed[minMatchLength],
hashPower);
rollingHash = ZSTD_rollingHash_rotate(rollingHash, lastHashed[0],
lastHashed[minMatchLength],
hashPower);
} else {
rollingHash = ZSTD_ldm_getRollingHash(ip, minMatchLength);
rollingHash = ZSTD_rollingHash_compute(ip, minMatchLength);
}
lastHashed = ip;