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Fix lowLimit underflow in overflow correction #1957

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merged 2 commits into from
Jan 18, 2020
Merged

Fix lowLimit underflow in overflow correction #1957

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a11a927
Fix lowLimit underflow in overflow correction
terrelln Jan 17, 2020
009f388
Fix playTests.sh for 32-bit mode
terrelln Jan 17, 2020
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18 changes: 15 additions & 3 deletions lib/compress/zstd_compress_internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -745,7 +745,10 @@ MEM_STATIC U32 ZSTD_window_correctOverflow(ZSTD_window_t* window, U32 cycleLog,
*/
U32 const cycleMask = (1U << cycleLog) - 1;
U32 const current = (U32)((BYTE const*)src - window->base);
U32 const newCurrent = (current & cycleMask) + maxDist;
U32 const currentCycle0 = current & cycleMask;
/* Exclude zero so that newCurrent - maxDist >= 1. */
U32 const currentCycle1 = currentCycle0 == 0 ? (1U << cycleLog) : currentCycle0;
U32 const newCurrent = currentCycle1 + maxDist;
U32 const correction = current - newCurrent;
assert((maxDist & cycleMask) == 0);
assert(current > newCurrent);
Expand All @@ -754,8 +757,17 @@ MEM_STATIC U32 ZSTD_window_correctOverflow(ZSTD_window_t* window, U32 cycleLog,

window->base += correction;
window->dictBase += correction;
window->lowLimit -= correction;
window->dictLimit -= correction;
if (window->lowLimit <= correction) window->lowLimit = 1;
else window->lowLimit -= correction;
if (window->dictLimit <= correction) window->dictLimit = 1;
else window->dictLimit -= correction;

/* Ensure we can still reference the full window. */
assert(newCurrent >= maxDist);
assert(newCurrent - maxDist >= 1);
/* Ensure that lowLimit and dictLimit didn't underflow. */
assert(window->lowLimit <= newCurrent);
assert(window->dictLimit <= newCurrent);

DEBUGLOG(4, "Correction of 0x%x bytes to lowLimit=0x%x", correction,
window->lowLimit);
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4 changes: 2 additions & 2 deletions tests/playTests.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -1239,8 +1239,8 @@ roundTripTest -g18000017 -P88 17
roundTripTest -g18000018 -P94 18
roundTripTest -g18000019 -P96 19

roundTripTest -g5000000000 -P99 1
roundTripTest -g1700000000 -P0 "1 --zstd=strategy=6" # ensure btlazy2 can survive an overflow rescale
roundTripTest -g5000000000 -P99 "1 --zstd=wlog=25"
roundTripTest -g3700000000 -P0 "1 --zstd=strategy=6,wlog=25" # ensure btlazy2 can survive an overflow rescale

fileRoundTripTest -g4193M -P99 1

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