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Hoist Hash Table Writes Up into Each Match Found Block

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Refactoring this way avoids the bad write in the case that `step > 4`, and
is a bit more straightforward. It also seems to perform better!
This commit is contained in:
W. Felix Handte 2022-05-11 11:27:34 -04:00
parent 040986a4f4
commit cd1f582943
1 changed files with 13 additions and 5 deletions
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18
lib/compress/zstd_fast.c
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@ -182,6 +182,10 @@ _start: /* Requires: ip0 */
match0 -= mLength;
offcode = REPCODE1_TO_OFFBASE;
mLength += 4;
/* first write next hash table entry; we've already calculated it */
hashTable[hash1] = (U32)(ip1 - base);
goto _match;
}
@ -195,6 +199,10 @@ _start: /* Requires: ip0 */
/* check match at ip[0] */
if (MEM_read32(ip0) == mval) {
/* found a match! */
/* first write next hash table entry; we've already calculated it */
hashTable[hash1] = (U32)(ip1 - base);
goto _offset;
}
@ -224,7 +232,9 @@ _start: /* Requires: ip0 */
/* check match at ip[0] */
if (MEM_read32(ip0) == mval) {
/* found a match! */
if (step > 4) {
/* first write next hash table entry; we've already calculated it */
if (step <= 4) {
/* We need to avoid writing an index into the hash table >= the
* position at which we will pick up our searching after we've
* taken this match.
@ -239,8 +249,9 @@ _start: /* Requires: ip0 */
* this is the only match path where this can occur. (In rep-
* code and the first match checks, ip1 == ip0 + 1.)
*/
ip1 = base;
hashTable[hash1] = (U32)(ip1 - base);
}
goto _offset;
}
@ -304,9 +315,6 @@ _match: /* Requires: ip0, match0, offcode */
ip0 += mLength;
anchor = ip0;
/* write next hash table entry */
hashTable[hash1] = (U32)(ip1 - base);
/* Fill table and check for immediate repcode. */
if (ip0 <= ilimit) {
/* Fill Table */