1 #ifndef JEMALLOC_INTERNAL_DIV_H
2 #define JEMALLOC_INTERNAL_DIV_H
4 #include "jemalloc/internal/assert.h"
7 * This module does the division that computes the index of a region in a slab,
8 * given its offset relative to the base.
9 * That is, given a divisor d, an n = i * d (all integers), we'll return i.
10 * We do some pre-computation to do this more quickly than a CPU division
12 * We bound n < 2^32, and don't support dividing by one.
15 typedef struct div_info_s div_info_t;
23 void div_init(div_info_t *div_info, size_t divisor);
26 div_compute(div_info_t *div_info, size_t n) {
27 assert(n <= (uint32_t)-1);
29 * This generates, e.g. mov; imul; shr on x86-64. On a 32-bit machine,
30 * the compilers I tried were all smart enough to turn this into the
31 * appropriate "get the high 32 bits of the result of a multiply" (e.g.
32 * mul; mov edx eax; on x86, umull on arm, etc.).
34 size_t i = ((uint64_t)n * (uint64_t)div_info->magic) >> 32;
36 assert(i * div_info->d == n);
41 #endif /* JEMALLOC_INTERNAL_DIV_H */