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Fix ZSTD_countTrailingZeros() bug

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`>> 3` is wrong.
This commit is contained in:
Ma Lin
2021-09-29 07:20:09 +08:00
parent ae986fcdb8
commit 894f05e88d
1 changed files with 7 additions and 7 deletions
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lib/common/zstd_internal.h
+7 -7
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@@ -385,10 +385,10 @@ MEM_STATIC U32 ZSTD_highbit32(U32 val) /* compress, dictBuilder, decodeCorpus
} }
/** /**
* Computes CTZ on a U64. * Counts the number of trailing zeros of a `size_t`.
* This will be slow on 32-bit mode, and on unsupported compilers. * Most compilers should support CTZ as a builtin. A backup
* If you need this function to be fast (because it is hot) expand * implementation is provided if the builtin isn't supported, but
* support. * it may not be terribly efficient.
*/ */
MEM_STATIC unsigned ZSTD_countTrailingZeros(size_t val) MEM_STATIC unsigned ZSTD_countTrailingZeros(size_t val)
{ {
@@ -400,7 +400,7 @@ MEM_STATIC unsigned ZSTD_countTrailingZeros(size_t val)
if (val != 0) { if (val != 0) {
unsigned long r; unsigned long r;
_BitScanForward64(&r, (U64)val); _BitScanForward64(&r, (U64)val);
return (unsigned)(r >> 3); return (unsigned)r;
} else { } else {
/* Should not reach this code path */ /* Should not reach this code path */
__assume(0); __assume(0);
@@ -424,13 +424,13 @@ MEM_STATIC unsigned ZSTD_countTrailingZeros(size_t val)
if (val != 0) { if (val != 0) {
unsigned long r; unsigned long r;
_BitScanForward(&r, (U32)val); _BitScanForward(&r, (U32)val);
return (unsigned)(r >> 3); return (unsigned)r;
} else { } else {
/* Should not reach this code path */ /* Should not reach this code path */
__assume(0); __assume(0);
} }
# elif defined(__GNUC__) && (__GNUC__ >= 3) # elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_ctz((U32)val) >> 3); return __builtin_ctz((U32)val);
# else # else
static const int DeBruijnBytePos[32] = { 0, 1, 28, 2, 29, 14, 24, 3, static const int DeBruijnBytePos[32] = { 0, 1, 28, 2, 29, 14, 24, 3,
30, 22, 20, 15, 25, 17, 4, 8, 30, 22, 20, 15, 25, 17, 4, 8,