'\" 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 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-08-10 by Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.TH copysign 3 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
copysign, copysignf, copysignl \- copy sign of a number
.SH LIBRARY
Math library
.RI ( libm ", " \-lm )
.SH SYNOPSIS
.nf
.B #include <math.h>
.PP
.BI "double copysign(double " x ", double " y );
.BI "float copysignf(float " x ", float " y );
.BI "long double copysignl(long double " x ", long double " y );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR copysign (),
.BR copysignf (),
.BR copysignl ():
.nf
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.fi
.SH DESCRIPTION
These functions return a value whose absolute value matches that of
.IR x ,
but whose sign bit matches that of
.IR y .
.PP
For example,
.I "copysign(42.0,\ \-1.0)"
and
.I "copysign(\-42.0, \-1.0)"
both return \-42.0.
.SH RETURN VALUE
On success, these functions return a value whose magnitude is taken from
.I x
and whose sign is taken from
.IR y .
.PP
If
.I x
is a NaN,
a NaN with the sign bit of
.I y
is returned.
.SH ERRORS
No errors occur.
.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 copysign (),
.BR copysignf (),
.BR copysignl ()
T}	Thread safety	MT-Safe
.TE
.sp 1
.SH VERSIONS
On architectures where the floating-point formats are not IEEE 754 compliant,
these functions may treat a negative zero as positive.
.SH STANDARDS
C11, POSIX.1-2008.
.PP
This function is defined in IEC 559 (and the appendix with
recommended functions in IEEE 754/IEEE 854).
.SH HISTORY
C99, POSIX.1-2001, 4.3BSD.
.SH SEE ALSO
.BR signbit (3)