fast_divide32_prepare(3) [netbsd man page]

FAST_DIVIDE32(3)					   BSD 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 con-
     stants 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.

BSD
								   May 10, 2011 							       BSD

Check Out this Related Man Page

DIV(3)							   BSD Library Functions Manual 						    DIV(3)

NAME

     div, ldiv, lldiv, imaxdiv -- quotient and remainder from division

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdlib.h>

     div_t
     div(int num, int denom);

     ldiv_t
     ldiv(long int num, long int denom);

     lldiv_t
     lldiv(long long int num, long long int denom);

     #include <inttypes.h>

     imaxdiv_t
     imaxdiv(intmax_t num, intmax_t denom);

DESCRIPTION

     These functions compute the value of num / denom and return the quotient and remainder in a specific divison structure.  The functions differ
     only with respect to the type of the return value and the parameters.

     The returned structure always contains two members named quot and rem, denoting the quotient and the remainder.  The type of these correspond
     with the underlying type of the function.

EXAMPLES

     The following example demonstrate the basic usage of the functions.

	   div_t d;

	   int a = 4321;
	   int b = 1234;

	   d = div(a, b);

	   (void)printf("%d %d
", d.quot, d.rem);

SEE ALSO

     fast_divide32(3), math(3), qdiv(3)

STANDARDS

     All described functions conform to ISO/IEC 9899:1999 (``ISO C99'').

BSD
								  April 13, 2011							       BSD

Linux and UNIX Man Pages

fast_divide32_prepare(3) [netbsd man page]

Check Out this Related Man Page