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FAST_DIVIDE32(3) Library Functions Manual FAST_DIVIDE32(3) NAME fast_divide32, fast_divide32_prepare, fast_remainder32 -- fast 32bit division and remainder SYNOPSIS #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); DESCRIPTION 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. RATIONALE These functions are useful for inner loops and other performance- sensitive tasks. The functions expand to code that is typically slightly larger than a plain division instruction, but requires less time to execute. The code for constant div arguments should be equivalent to the assembly created by GCC. EXAMPLES 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); SEE ALSO bitops(3), div(3), remainder(3) Torbjorn Granlund and Peter L. Montgomery, "Division by Invariant Integers Using Multiplication", ACM SIGPLAN Notices, Issue 6, Volume 29, http://gmplib.org/~tege/divcnst-pldi94.pdf, 61-72, June 1994. HISTORY The fast_divide32 function appeared in NetBSD 6.0. NetBSD 7.1.2 May 10, 2011 NetBSD 7.1.2