ddidderr/zstd-rs
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Replace XOR with subtraction for readability

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This commit is contained in:
Elliot Gorokhovsky
2022-02-16 16:49:42 -05:00
parent 856c7dc51d
commit 71d9dab76f
2 changed files with 5 additions and 5 deletions
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lib/common/bits.h
+4 -4
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@@ -60,7 +60,7 @@ MEM_STATIC unsigned ZSTD_countLeadingZeros32_fallback(U32 val) {
val |= val >> 4; val |= val >> 4;
val |= val >> 8; val |= val >> 8;
val |= val >> 16; val |= val >> 16;
return DeBruijnClz[(val * 0x07C4ACDDU) >> 27] ^ 31; return 31 - DeBruijnClz[(val * 0x07C4ACDDU) >> 27];
} }
} }
@@ -74,7 +74,7 @@ MEM_STATIC unsigned ZSTD_countLeadingZeros32(U32 val)
if (val != 0) { if (val != 0) {
unsigned long r; unsigned long r;
_BitScanReverse(&r, val); _BitScanReverse(&r, val);
return (unsigned)(r ^ 31); return (unsigned)(31 - r);
} else { } else {
/* Should not reach this code path */ /* Should not reach this code path */
__assume(0); __assume(0);
@@ -128,7 +128,7 @@ MEM_STATIC unsigned ZSTD_countLeadingZeros64(U64 val)
if (val != 0) { if (val != 0) {
unsigned long r; unsigned long r;
_BitScanReverse64(&r, val); _BitScanReverse64(&r, val);
return (unsigned)(r ^ 63); return (unsigned)(63 - r);
} else { } else {
/* Should not reach this code path */ /* Should not reach this code path */
__assume(0); __assume(0);
@@ -169,7 +169,7 @@ MEM_STATIC unsigned ZSTD_NbCommonBytes(size_t val)
MEM_STATIC unsigned ZSTD_highbit32(U32 val) /* compress, dictBuilder, decodeCorpus */ MEM_STATIC unsigned ZSTD_highbit32(U32 val) /* compress, dictBuilder, decodeCorpus */
{ {
assert(val != 0); assert(val != 0);
return ZSTD_countLeadingZeros32(val) ^ 31; return 31 - ZSTD_countLeadingZeros32(val);
} }
#endif /* ZSTD_BITS_H */ #endif /* ZSTD_BITS_H */
tests/fuzzer.c
+1 -1
View File
@@ -3375,7 +3375,7 @@ static int basicUnitTests(U32 const seed, double compressibility)
} }
DISPLAYLEVEL(3, "OK \n"); DISPLAYLEVEL(3, "OK \n");
DISPLAYLEVEL(3, "test%3i : testing bitwise instrinsics PR#3045: ", testNb++); DISPLAYLEVEL(3, "test%3i : testing bitwise intrinsics PR#3045: ", testNb++);
{ {
U32 seed_copy = seed; // need non-const seed to avoid compiler warning for FUZ_rand(&seed) U32 seed_copy = seed; // need non-const seed to avoid compiler warning for FUZ_rand(&seed)
U32 rand32 = FUZ_rand(&seed_copy); U32 rand32 = FUZ_rand(&seed_copy);