'\" 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 2024-05-02 "Linux man-pages 6.9.1" .SH NAME copysign, copysignf, copysignl \- copy sign of a number .SH LIBRARY Math library .RI ( libm ", " \-lm ) .SH SYNOPSIS .nf .B #include .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)