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Bug fix & run overflow correction much more frequently in tests

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* Fix overflow correction when `windowLog < cycleLog`. Previously, we
  got the correction wrong in this case, and our chain tables and binary
  trees would be corrupted. Now, we work as long as `maxDist` is a power
  of two, by adding `MAX(maxDist, cycleSize)` to our indices.
* When `ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY` is defined to non-zero
  run overflow correction as frequently as allowed without impacting
  compression ratio.
* Enable `ZSTD_WINDOW_OVERFLOW_CORRECT_FREQUENTLY` in `fuzzer` and
  `zstreamtest` as well as all the OSS-Fuzz fuzzers. This has a 5-10%
  speed penalty at most, which seems reasonable.
This commit is contained in:
Nick Terrell
2021-05-03 15:21:47 -07:00
parent cc31bb8b66
commit 34aff7ea06
5 changed files with 62 additions and 14 deletions
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lib/compress/zstd_compress.c
+3 -3
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@@ -3803,9 +3803,9 @@ static void ZSTD_overflowCorrectIfNeeded(ZSTD_matchState_t* ms,
void const* ip,
void const* iend)
{
if (ZSTD_window_needOverflowCorrection(ms->window, iend)) {
U32 const maxDist = (U32)1 << params->cParams.windowLog;
U32 const cycleLog = ZSTD_cycleLog(params->cParams.chainLog, params->cParams.strategy);
U32 const cycleLog = ZSTD_cycleLog(params->cParams.chainLog, params->cParams.strategy);
U32 const maxDist = (U32)1 << params->cParams.windowLog;
if (ZSTD_window_needOverflowCorrection(ms->window, cycleLog, maxDist, ms->loadedDictEnd, ip, iend)) {
U32 const correction = ZSTD_window_correctOverflow(&ms->window, cycleLog, maxDist, ip);
ZSTD_STATIC_ASSERT(ZSTD_CHAINLOG_MAX <= 30);
ZSTD_STATIC_ASSERT(ZSTD_WINDOWLOG_MAX_32 <= 30);