FAST_DIVIDE32(3) BSD Library Functions Manual FAST_DIVIDE32(3)NAME
fast_divide32, fast_divide32_prepare, fast_remainder32 — fast 32bit divi‐
sion 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-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.
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 ALSObitops(3), div(3), remainder(3)
Torbjörn 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.
BSD May 10, 2011 BSD
