man3/copysign.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  30 .\" Modified 2002-08-10 by Walter Harms (walter.harms@informatik.uni-oldenburg.de)
  31 .TH COPYSIGN 3  2017-09-15 "GNU" "Linux Programmer's Manual"
  32 .SH NAME
  33 copysign, copysignf, copysignl \- copy sign of a number
  34 .SH SYNOPSIS
  35 .nf
  36 .B #include <math.h>
  37 .PP
  38 .BI "double copysign(double " x ", double " y );
  39 .BI "float copysignf(float " x ", float " y );
  40 .BI "long double copysignl(long double " x ", long double " y );
  41 .fi
  42 .PP
  43 Link with \fI\-lm\fP.
  44 .PP
  45 .in -4n
  46 Feature Test Macro Requirements for glibc (see
  47 .BR feature_test_macros (7)):
  48 .in
  49 .PP
  50 .ad l
  51 .BR copysign (),
  52 .BR copysignf (),
  53 .BR copysignl ():
  54 .RS 4
  55 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  56     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  57     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  58 .RE
  59 .ad b
  60 .SH DESCRIPTION
  61 These functions return a value whose absolute value matches that of
  62 .IR x ,
  63 but whose sign bit matches that of
  64 .IR y .
  65 .PP
  66 For example,
  67 .I "copysign(42.0,\ \-1.0)"
  68 and
  69 .I "copysign(\-42.0, \-1.0)"
  70 both return \-42.0.
  71 .SH RETURN VALUE
  72 On success, these functions return a value whose magnitude is taken from
  73 .I x
  74 and whose sign is taken from
  75 .IR y .
  76 .PP
  77 If
  78 .I x
  79 is a NaN,
  80 a NaN with the sign bit of
  81 .I y
  82 is returned.
  83 .SH ERRORS
  84 No errors occur.
  85 .SH ATTRIBUTES
  86 For an explanation of the terms used in this section, see
  87 .BR attributes (7).
  88 .TS
  89 allbox;
  90 lbw36 lb lb
  91 l l l.
  92 Interface       Attribute       Value
  93 T{
  94 .BR copysign (),
  95 .BR copysignf (),
  96 .BR copysignl ()
  97 T}      Thread safety   MT-Safe
  98 .TE
  99 .SH CONFORMING TO
 100 C99, POSIX.1-2001, POSIX.1-2008.
 101 .\" 4.3BSD.
 102 This function is defined in IEC 559 (and the appendix with
 103 recommended functions in IEEE 754/IEEE 854).
 104 .SH NOTES
 105 On architectures where the floating-point formats are not IEEE 754 compliant,
 106 these
 107 functions may treat a negative zero as positive.
 108 .SH SEE ALSO
 109 .BR signbit (3)