Adding upstream version 6.05.01.upstream/6.05.01

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+'\" t
+.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" References consulted:
+.\"     Linux libc source code
+.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
+.\"     386BSD man pages
+.\" Modified Sat Jul 24 18:55:27 1993 by Rik Faith (faith@cs.unc.edu)
+.TH memcmp 3 2023-07-30 "Linux man-pages 6.05.01"
+.SH NAME
+memcmp \- compare memory areas
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.B #include <string.h>
+.PP
+.BI "int memcmp(const void " s1 [. n "], const void " s2 [. n "], size_t " n );
+.fi
+.SH DESCRIPTION
+The
+.BR memcmp ()
+function compares the first \fIn\fP bytes (each interpreted as
+.IR "unsigned char" )
+of the memory areas \fIs1\fP and \fIs2\fP.
+.SH RETURN VALUE
+The
+.BR memcmp ()
+function returns an integer less than, equal to, or
+greater than zero if the first \fIn\fP bytes of \fIs1\fP is found,
+respectively, to be less than, to match, or be greater than the first
+\fIn\fP bytes of \fIs2\fP.
+.PP
+For a nonzero return value, the sign is determined by the sign of
+the difference between the first pair of bytes (interpreted as
+.IR "unsigned char" )
+that differ in
+.I s1
+and
+.IR s2 .
+.PP
+If
+.I n
+is zero, the return value is zero.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR memcmp ()
+T}	Thread safety	MT-Safe
+.TE
+.sp 1
+.SH STANDARDS
+C11, POSIX.1-2008.
+.SH HISTORY
+POSIX.1-2001, C89, SVr4, 4.3BSD.
+.SH CAVEATS
+Do not use
+.BR memcmp ()
+to compare confidential data,
+such as cryptographic secrets,
+because the CPU time required for the comparison
+depends on the contents of the addresses compared,
+this function is subject to timing-based side-channel attacks.
+In such cases,
+a function that performs comparisons in deterministic time,
+depending only on
+.I n
+(the quantity of bytes compared)
+is required.
+Some operating systems provide such a function (e.g., NetBSD's
+.BR consttime_memequal ()),
+but no such function is specified in POSIX.
+On Linux, you may need to implement such a function yourself.
+.SH SEE ALSO
+.BR bstring (3),
+.BR strcasecmp (3),
+.BR strcmp (3),
+.BR strcoll (3),
+.BR strncasecmp (3),
+.BR strncmp (3),
+.BR wmemcmp (3)