fast_divide32(3) - NetBSD Manual Pages

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FAST_DIVIDE32(3)        NetBSD Library Functions Manual       FAST_DIVIDE32(3)

fast_divide32, fast_divide32_prepare, fast_remainder32 -- fast 32bit division and remainder
#include <sys/bitops.h> uint32_t fast_divide32(uint32_t v, uint32_t div, uint32_t m, uint8_t s1, uint8_t s2); uint32_t fast_remainder32(uint32_t v, uint32_t div, uint32_t m, uint8_t s1, uint8_t s2); void fast_divide32_prepare(uint32_t div, uint32_t *m, uint8_t *s1, uint8_t *s2);
The fast_divide32 and fast_remainder32 functions compute the equivalent of v / div and v % div using optimised CPU instructions. The constants m, s1, and s2 must first be preset for a given value of div with the fast_divide32_prepare function.
These functions are useful for inner loops and other performance-sensi- tive tasks. The functions expand to code that is typically slightly larger than a plain division instruction, but requires less time to exe- cute. The code for constant div arguments should be equivalent to the assembly created by GCC.
The following example computes q = a / b and r = a % b: uint32_t a, b, q, r, m; uint8_t s1, s2; fast_divide32_prepare(b, &m, &s1, &s2); q = fast_divide32(a, b, m, s1, s2); r = fast_remainder32(a, b, m, s1, s2);
bitops(3), div(3), remainder(3) Torbjörn Granlund and Peter L. Montgomery, "Division by Invariant Integers Using Multiplication", ACM SIGPLAN Notices, Issue 6, Volume 29,, 61-72, June 1994.
The fast_divide32 function appeared in NetBSD 6.0. NetBSD 9.1 May 10, 2011 NetBSD 9.1
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