man3/signbit.3

   1 .\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\" Distributed under GPL
   3 .\" Based on glibc infopages
   4 .TH SIGNBIT 3 2002-08-10 "GNU" "libc math functions"
   5 .SH NAME
   6 signbit \- test sign of a real floating point number
   7 .SH SYNOPSIS
   8 .B "#include <math.h>"
   9 .sp
  10 .BI  "int signbit (" X ");"
  11 .sp
  12 Compile with -std=c99; link with \-lm.
  13 .SH DESCRIPTION
  14 `signbit' is a generic macro which can work on all real floating-point
  15 types.  It returns a nonzero value if the value of X has its sign
  16 bit set.
  17 .PP
  18 This is not the same as `x < 0.0', because IEEE 754 floating point
  19 allows zero to be signed.  The comparison `-0.0 < 0.0' is false,
  20 but `signbit (-0.0)' will return a nonzero value.
  21 .SH "CONFORMING TO"
  22 This function is defined in IEC 559 (and the appendix with
  23 recommended functions in IEEE 754/IEEE 854).
  24 .SH "SEE ALSO"
  25 .BR copysign (3)