1.\" $NetBSD: fast_divide32.3,v 1.10 2024/09/07 20:33:53 rillig Exp $ 2.\" 3.\" Copyright (c) 2010 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Joerg Sonnenberger. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd May 10, 2011 31.Dt FAST_DIVIDE32 3 32.Os 33.Sh NAME 34.Nm fast_divide32 , 35.Nm fast_divide32_prepare , 36.Nm fast_remainder32 37.Nd fast 32bit division and remainder 38.Sh SYNOPSIS 39.In sys/bitops.h 40.Ft uint32_t 41.Fn fast_divide32 "uint32_t v" "uint32_t div" "uint32_t m" "uint8_t s1" \ 42"uint8_t s2" 43.Ft uint32_t 44.Fn fast_remainder32 "uint32_t v" "uint32_t div" "uint32_t m" "uint8_t s1" \ 45"uint8_t s2" 46.Ft void 47.Fn fast_divide32_prepare "uint32_t div" "uint32_t *m" "uint8_t *s1" \ 48"uint8_t *s2" 49.Sh DESCRIPTION 50The 51.Nm fast_divide32 52and 53.Nm fast_remainder32 54functions compute the equivalent of 55.Fa v / Fa div 56and 57.Fa v % Fa div 58using optimised 59.Tn CPU 60instructions. 61The constants 62.Fa m , 63.Fa s1 , 64and 65.Fa s2 66must first be preset for a given value of 67.Fa div 68with the 69.Nm fast_divide32_prepare 70function. 71.Sh RATIONALE 72These functions are useful for inner loops and other performance-sensitive 73tasks. 74The functions expand to code that is typically slightly larger than 75a plain division instruction, but requires less time to execute. 76The code for constant 77.Fa div 78arguments should be equivalent to the assembly created by 79.Tn GCC . 80.Sh EXAMPLES 81The following example computes 82.Va q = a / b 83and 84.Va r = a % b : 85.Bd -literal -offset indent 86uint32_t a, b, q, r, m; 87uint8_t s1, s2; 88 89fast_divide32_prepare(b, &m, &s1, &s2); 90 91q = fast_divide32(a, b, m, s1, s2); 92r = fast_remainder32(a, b, m, s1, s2); 93.Ed 94.Sh SEE ALSO 95.Xr bitops 3 , 96.Xr div 3 , 97.Xr remainder 3 98.Rs 99.%A Torbj\(:orn Granlund 100.%A Peter L. Montgomery 101.%T Division by Invariant Integers Using Multiplication 102.%J ACM SIGPLAN Notices 103.%D June 1994 104.%N Issue 6 105.%V Volume 29 106.%P 61-72 107.%U https://gmplib.org/~tege/divcnst-pldi94.pdf 108.Re 109.Sh HISTORY 110The 111.Nm 112function appeared in 113.Nx 6.0 . 114