FAST_DIVIDE32(3) BSD Library Functions Manual FAST_DIVIDE32(3)
fast_divide32, fast_divide32_prepare, fast_remainder32 -- fast 32bit division and remainder
fast_divide32(uint32_t v, uint32_t div, uint32_t m, uint8_t s1, uint8_t s2);
fast_remainder32(uint32_t v, uint32_t div, uint32_t m, uint8_t s1, uint8_t s2);
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-sensitive tasks. The func-
tions 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.
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)
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.
The fast_divide32 function appeared in NetBSD 6.0.
BSD May 10, 2011 BSD