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Bit_util: Use intrinsics for pow2_ceil, where available.

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Rajeev Misra 2018-08-10 20:27:35 -07:00 committed by David Goldblatt
parent 36eb0b3d77
commit 4c548a61c8
1 changed files with 34 additions and 0 deletions
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34
include/jemalloc/internal/bit_util.h
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@ -63,6 +63,22 @@ ffs_u32(uint32_t bitmap) {
BIT_UTIL_INLINE uint64_t
pow2_ceil_u64(uint64_t x) {
#if (defined(__amd64__) || defined(__x86_64__) || defined(JEMALLOC_HAVE_BUILTIN_CLZ))
if(unlikely(x <= 1)) {
return x;
}
size_t msb_on_index;
#if (defined(__amd64__) || defined(__x86_64__))
asm ("bsrq %1, %0"
: "=r"(msb_on_index) // Outputs.
: "r"(x-1) // Inputs.
);
#elif (defined(JEMALLOC_HAVE_BUILTIN_CLZ))
msb_on_index = (63 ^ __builtin_clzll(x - 1));
#endif
assert(msb_on_index < 63);
return 1ULL << (msb_on_index + 1);
#else
x--;
x |= x >> 1;
x |= x >> 2;
@ -72,10 +88,27 @@ pow2_ceil_u64(uint64_t x) {
x |= x >> 32;
x++;
return x;
#endif
}
BIT_UTIL_INLINE uint32_t
pow2_ceil_u32(uint32_t x) {
#if (defined(__i386__) || defined(JEMALLOC_HAVE_BUILTIN_CLZ))
if(unlikely(x <= 1)) {
return x;
}
size_t msb_on_index;
#if (defined(__i386__))
asm ("bsr %1, %0"
: "=r"(msb_on_index) // Outputs.
: "r"(x-1) // Inputs.
);
#elif (defined(JEMALLOC_HAVE_BUILTIN_CLZ))
msb_on_index = (31 ^ __builtin_clz(x - 1));
#endif
assert(msb_on_index < 31);
return 1U << (msb_on_index + 1);
#else
x--;
x |= x >> 1;
x |= x >> 2;
@ -84,6 +117,7 @@ pow2_ceil_u32(uint32_t x) {
x |= x >> 16;
x++;
return x;
#endif
}
/* Compute the smallest power of 2 that is >= x. */