diff --git a/lib/libc/string/memcmp.3 b/lib/libc/string/memcmp.3 index e7666fe6d605..8f4980d61c05 100644 --- a/lib/libc/string/memcmp.3 +++ b/lib/libc/string/memcmp.3 @@ -1,82 +1,91 @@ .\" Copyright (c) 1990, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" Chris Torek and the American National Standards Committee X3, .\" on Information Processing Systems. .\" .\" 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. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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 August 15, 2016 +.Dd November 20, 2024 .Dt MEMCMP 3 .Os .Sh NAME .Nm memcmp -.Nd compare byte string +.Nd compare bytes in memory .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In string.h .Ft int .Fn memcmp "const void *b1" "const void *b2" "size_t len" .Sh DESCRIPTION The .Fn memcmp function -compares byte string +compares byte object .Fa b1 -against byte string +against byte object .Fa b2 . -Both strings are assumed to be +Both objects are assumed to be .Fa len bytes long. .Sh RETURN VALUES The .Fn memcmp -function -returns zero if the two strings are identical, -otherwise returns the difference between the first two differing bytes -(treated as -.Vt "unsigned char" -values, so that -.Sq Li \e200 -is greater than -.Sq Li \&\e0 , -for example). -Zero-length strings are always identical. +function returns zero if the two objects are identical. +Zero-length objects are considered identical. +The +.Fn memcmp +function returns a negative value if the first differing byte has a lower +value in +.Fa b1 +and a positive value if the first differing byte has a higher value in +.Fa b1 . .Sh SEE ALSO .Xr bcmp 3 , .Xr strcasecmp 3 , .Xr strcmp 3 , .Xr strcoll 3 , .Xr strxfrm 3 , .Xr timingsafe_memcmp 3 , .Xr wmemcmp 3 .Sh STANDARDS The .Fn memcmp function conforms to .St -isoC . +.Sh CAVEATS +If the objects differ, the C library +.Fn memcmp +implementation returns the difference between the first two differing bytes +.Po treated as +.Vt "unsigned char" +values +.Pc . +This behavior is not specified by +.St -isoC , +is not portable, and may not occur in light of compiler optimizations.