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Use intrinsics instead

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Thor Preimesberger 2025-09-23 17:55:57 -04:00
parent 42a635282a
commit 592a25aaeb
1 changed files with 6 additions and 13 deletions
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19
h_malloc.c
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@ -20,6 +20,10 @@
#include "random.h"
#include "util.h"
#if __x86_64__
#include "immintrin.h"
#endif
#ifdef USE_PKEY
#include <sys/mman.h>
#endif
@ -405,19 +409,8 @@ static size_t get_free_slot(struct random_state *rng, size_t slots, const struct
// randomize start location for linear search (uniform random choice is too slow)
size_t random_index = get_random_u16_uniform(rng, slots);
size_t first_bitmap = random_index / U64_WIDTH;
#if __x86_64__ && __BMI2__
u64 tmp;
__asm__ (
// set up mask
"mov $0xfffffffffffffff8, %1\n\t"
// tmp is now same as shift amount mod 256 in portable case
"pext %[tmp], %[random_index], %1\n\t"
: [tmp] "=r" (tmp)
: [random_index] "r" (random_index));
// gcc/clang is smart enough to generate code with no spills here
u64 random_split = ~(~0UL << (tmp));
#if __x86_64__ && (__BMI2__)
u64 random_split = ~(~0UL << _pext_u64(random_index, 8));
#else
u64 random_split = ~(~0UL << (random_index - first_bitmap * U64_WIDTH));
#endif