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Use _BitScanForward and _BitScanReverse on MSVC.

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Based on https://github.com/google/snappy/pull/30
This commit is contained in:
costan
2017-08-01 10:01:27 -07:00
committed by Victor Costan
parent 71b8f86887
commit f0d3237c32
1 changed files with 36 additions and 0 deletions
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36
snappy-stubs-internal.h
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@@ -45,6 +45,10 @@
#include <sys/mman.h>
#endif
#if defined(_MSC_VER)
#include <intrin.h>
#endif // defined(_MSC_VER)
#include "snappy-stubs-public.h"
#if defined(__x86_64__)
@@ -347,7 +351,10 @@ class Bits {
// undefined value if n == 0. FindLSBSetNonZero() is similar to ffs() except
// that it's 0-indexed.
static int FindLSBSetNonZero(uint32 n);
#if defined(ARCH_K8) || defined(ARCH_PPC)
static int FindLSBSetNonZero64(uint64 n);
#endif // defined(ARCH_K8) || defined(ARCH_PPC)
private:
// No copying
@@ -365,9 +372,36 @@ inline int Bits::FindLSBSetNonZero(uint32 n) {
return __builtin_ctz(n);
}
#if defined(ARCH_K8) || defined(ARCH_PPC)
inline int Bits::FindLSBSetNonZero64(uint64 n) {
return __builtin_ctzll(n);
}
#endif // defined(ARCH_K8) || defined(ARCH_PPC)
#elif defined(_MSC_VER)
inline int Bits::Log2Floor(uint32 n) {
unsigned long where;
if (_BitScanReverse(&where, n)) {
return where;
} else {
return -1;
}
}
inline int Bits::FindLSBSetNonZero(uint32 n) {
unsigned long where;
if (_BitScanForward(&where, n)) return static_cast<int>(where);
return 32;
}
#if defined(ARCH_K8) || defined(ARCH_PPC)
inline int Bits::FindLSBSetNonZero64(uint64 n) {
unsigned long where;
if (_BitScanForward64(&where, n)) return static_cast<int>(where);
return 64;
}
#endif // defined(ARCH_K8) || defined(ARCH_PPC)
#else // Portable versions.
@@ -401,6 +435,7 @@ inline int Bits::FindLSBSetNonZero(uint32 n) {
return rc;
}
#if defined(ARCH_K8) || defined(ARCH_PPC)
// FindLSBSetNonZero64() is defined in terms of FindLSBSetNonZero().
inline int Bits::FindLSBSetNonZero64(uint64 n) {
const uint32 bottombits = static_cast<uint32>(n);
@@ -411,6 +446,7 @@ inline int Bits::FindLSBSetNonZero64(uint64 n) {
return FindLSBSetNonZero(bottombits);
}
}
#endif // defined(ARCH_K8) || defined(ARCH_PPC)
#endif // End portable versions.