$NetBSD: fast_divide32.3,v 1.9 2017/07/03 21:30:58 wiz Exp $
Copyright (c) 2010 The NetBSD Foundation, Inc.
All rights reserved.
This code is derived from software contributed to The NetBSD Foundation
by Joerg Sonnenberger.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
.Dd May 10, 2011 .Dt FAST_DIVIDE32 3 .Os .Sh NAME .Nm fast_divide32 , .Nm fast_divide32_prepare , .Nm fast_remainder32 .Nd fast 32bit division and remainder .Sh SYNOPSIS n sys/bitops.h .Ft uint32_t .Fn fast_divide32 "uint32_t v" "uint32_t div" "uint32_t m" "uint8_t s1" \ "uint8_t s2" .Ft uint32_t .Fn fast_remainder32 "uint32_t v" "uint32_t div" "uint32_t m" "uint8_t s1" \ "uint8_t s2" .Ft void .Fn fast_divide32_prepare "uint32_t div" "uint32_t *m" "uint8_t *s1" \ "uint8_t *s2" .Sh DESCRIPTION The .Nm fast_divide32 and .Nm fast_remainder32 functions compute the equivalent of .Fa v / Fa div and .Fa v % Fa div using optimised .Tn CPU instructions. The constants .Fa m , .Fa s1 , and .Fa s2 must first be preset for a given value of .Fa div with the .Nm fast_divide32_prepare function. .Sh 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 .Fa div arguments should be equivalent to the assembly created by .Tn GCC . .Sh EXAMPLES The following example computes .Va q = a / b and .Va r = a % b : d -literal -offset indent 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); .Ed .Sh SEE ALSO .Xr bitops 3 , .Xr div 3 , .Xr remainder 3 .Rs .%A Torbj\(:orn Granlund .%A Peter L. Montgomery .%T Division by Invariant Integers Using Multiplication .%J ACM SIGPLAN Notices .%D June 1994 .%N Issue 6 .%V Volume 29 .%P 61-72 .%U http://gmplib.org/~tege/divcnst-pldi94.pdf .Re .Sh HISTORY The .Nm function appeared in .Nx 6.0 .
Copyright (c) 2010 The NetBSD Foundation, Inc.
All rights reserved.
This code is derived from software contributed to The NetBSD Foundation
by Joerg Sonnenberger.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
.Dd May 10, 2011 .Dt FAST_DIVIDE32 3 .Os .Sh NAME .Nm fast_divide32 , .Nm fast_divide32_prepare , .Nm fast_remainder32 .Nd fast 32bit division and remainder .Sh SYNOPSIS n sys/bitops.h .Ft uint32_t .Fn fast_divide32 "uint32_t v" "uint32_t div" "uint32_t m" "uint8_t s1" \ "uint8_t s2" .Ft uint32_t .Fn fast_remainder32 "uint32_t v" "uint32_t div" "uint32_t m" "uint8_t s1" \ "uint8_t s2" .Ft void .Fn fast_divide32_prepare "uint32_t div" "uint32_t *m" "uint8_t *s1" \ "uint8_t *s2" .Sh DESCRIPTION The .Nm fast_divide32 and .Nm fast_remainder32 functions compute the equivalent of .Fa v / Fa div and .Fa v % Fa div using optimised .Tn CPU instructions. The constants .Fa m , .Fa s1 , and .Fa s2 must first be preset for a given value of .Fa div with the .Nm fast_divide32_prepare function. .Sh 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 .Fa div arguments should be equivalent to the assembly created by .Tn GCC . .Sh EXAMPLES The following example computes .Va q = a / b and .Va r = a % b : d -literal -offset indent 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); .Ed .Sh SEE ALSO .Xr bitops 3 , .Xr div 3 , .Xr remainder 3 .Rs .%A Torbj\(:orn Granlund .%A Peter L. Montgomery .%T Division by Invariant Integers Using Multiplication .%J ACM SIGPLAN Notices .%D June 1994 .%N Issue 6 .%V Volume 29 .%P 61-72 .%U http://gmplib.org/~tege/divcnst-pldi94.pdf .Re .Sh HISTORY The .Nm function appeared in .Nx 6.0 .