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'\" t
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH copysign 3 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
copysign, copysignf, copysignl \- copy sign of a number
.SH LIBRARY
Math library
.RI ( libm ,\~ \-lm )
.SH SYNOPSIS
.nf
.B #include <math.h>
.P
.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
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.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 .
.P
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 .
.P
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
.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.
.P
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)
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