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) Torbjörn Granlund, Peter L. Montgomery, Division by Invariant Integers Using Multiplication, ACM SIGPLAN Notices, June 1994, Issue 6, Volume 29, 61-72, https://gmplib.org/~tege/divcnst-pldi94.pdf.

HISTORY
The fast_divide32 function appeared in NetBSD 6.0.