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Fix overflow protection with wlog=31

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The overflow protection is broken when the window log is `> (3U << 29)`, so 31.
It doesn't work when `current` isn't around `1U << windowLog` ahead of `lowLimit`,
and the the assertion `current > newCurrent` fails. This happens when the same
context is used many times over, but with a large window log, like in zstdmt.

Fix it by triggering correction based on `nextSrc - base` instead of `lowLimit`.

The added test fails before the patch, and passes after.
This commit is contained in:
Nick Terrell
2018-03-14 11:45:44 -07:00
parent 4c5cbac179
commit 33fb966e56
4 changed files with 34 additions and 16 deletions
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lib/compress/zstd_compress.c
+1 -1
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@@ -1902,7 +1902,7 @@ static size_t ZSTD_compress_frameChunk (ZSTD_CCtx* cctx,
return ERROR(dstSize_tooSmall); /* not enough space to store compressed block */
if (remaining < blockSize) blockSize = remaining;
if (ZSTD_window_needOverflowCorrection(ms->window)) {
if (ZSTD_window_needOverflowCorrection(ms->window, ip + blockSize)) {
U32 const cycleLog = ZSTD_cycleLog(cctx->appliedParams.cParams.chainLog, cctx->appliedParams.cParams.strategy);
U32 const correction = ZSTD_window_correctOverflow(&ms->window, cycleLog, maxDist, ip);
ZSTD_STATIC_ASSERT(ZSTD_CHAINLOG_MAX <= 30);