1.\" $NetBSD: bits.3,v 1.19 2020/06/08 17:28:10 sevan Exp $ 2.\" 3.\" Copyright (c) 2006, 2010 David Young. All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or 6.\" without modification, are permitted provided that the following 7.\" conditions are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above 11.\" copyright notice, this list of conditions and the following 12.\" disclaimer in the documentation and/or other materials 13.\" provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY DAVID YOUNG ``AS IS'' AND ANY 16.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, 17.\" THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 18.\" PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL DAVID 19.\" YOUNG BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 20.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 21.\" TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND 23.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 24.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 26.\" POSSIBILITY OF SUCH DAMAGE. 27.\" 28.Dd November 6, 2016 29.Dt BITS 3 30.Os 31.Sh NAME 32.Nm __BIT , 33.Nm __BITS , 34.Nm __SHIFTIN , 35.Nm __SHIFTOUT , 36.Nm __SHIFTOUT_MASK 37.Nd "macros for preparing bitmasks and operating on bit fields" 38.Sh SYNOPSIS 39.In sys/param.h 40.In sys/cdefs.h 41.Ft uintmax_t 42.Fn __BIT "n" 43.Ft uintmax_t 44.Fn __BITS "m" "n" 45.Fn __SHIFTIN "v" "mask" 46.Fn __SHIFTOUT "v" "mask" 47.Fn __SHIFTOUT_MASK "mask" 48.Sh DESCRIPTION 49These macros prepare bitmasks, extract bitfields from words, and 50insert bitfields into words. 51A 52.Dq bitfield 53is a span of consecutive bits defined by a bitmask, where 1s select 54the bits in the bitfield. 55.Pp 56Use 57.Fn __BIT 58and 59.Fn __BITS 60to define bitmasks: 61.Bl -tag -width __BITS -offset indent 62.It Fn __BIT "n" 63Return a bitmask with bit 64.Fa n 65set, where the least significant bit is bit 0. 66.It Fn __BITS "m" "n" 67Return a bitmask with bits 68.Fa m 69through 70.Fa n , 71inclusive, set. 72It does not matter whether 73.Fa m No > Fa n 74or 75.Fa m No <= Fa n . 76The least significant bit is bit 0. 77.El 78.Pp 79.Fn __SHIFTIN , 80.Fn __SHIFTOUT , 81and 82.Fn __SHIFTOUT_MASK 83help read and write bitfields from words: 84.Bl -tag -width __SHIFTOUT_MASK -offset indent 85.It Fn __SHIFTIN "v" "mask" 86Left-shift bits 87.Fa v 88into the bitfield defined by 89.Fa mask , 90and return them. 91No side-effects. 92.It Fn __SHIFTOUT "v" "mask" 93Extract and return the bitfield selected by 94.Fa mask 95from 96.Fa v , 97right-shifting the bits so that the rightmost selected bit is at 98bit 0. 99No side-effects. 100.It Fn __SHIFTOUT_MASK "mask" 101Right-shift the bits in 102.Fa mask 103so that the rightmost non-zero bit is at bit 0. 104This is useful for finding the greatest unsigned value that a 105bitfield can hold. 106No side-effects. 107Note that 108.Fn __SHIFTOUT_MASK "m" 109= 110.Fn __SHIFTOUT "m" "m" . 111.El 112.Sh EXAMPLES 113The following example demonstrates basic usage of the 114.Nm bits 115macros: 116.Bd -literal -offset indent 117uint32_t bits, mask, val; 118 119bits = __BITS(2, 3); /* 00001100 */ 120mask = __BIT(2) | __BIT(3); /* 00001100 */ 121 122val = __SHIFTIN(0x03, mask); /* 00001100 */ 123val = __SHIFTOUT(0xf, mask); /* 00000011 */ 124.Ed 125.Sh SEE ALSO 126.Xr bitops 3 , 127.Xr cdefs 3 128.Sh HISTORY 129The 130.Nm bits 131macros first appeared in 132.Xr atw 4 , 133with different names and implementation. 134In their current form these macros appeared in 135.Nx 4.0 . 136.Sh AUTHORS 137The 138.Nm bits 139macros were written by 140.An David Young Aq Mt dyoung@NetBSD.org . 141.An Matt Thomas Aq Mt matt@NetBSD.org 142suggested important improvements to the implementation, and 143contributed the macro names 144.Fn SHIFTIN 145and 146.Fn SHIFTOUT . 147