2004-11-03 13:51:07 +00:00
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.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
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.\" Distributed under GPL
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.\" Based on glibc infopages
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2007-05-18 08:43:42 +00:00
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.TH SIGNBIT 3 2002-08-10 "GNU" "Linux Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.SH NAME
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signbit \- test sign of a real floating point number
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.SH SYNOPSIS
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.B "#include <math.h>"
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.sp
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.BI "int signbit(" x ");"
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.sp
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2007-05-21 09:56:00 +00:00
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Compile with \fI\-std=c99\fP; link with \fI\-lm\fP.
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.SH DESCRIPTION
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.BR signbit ()
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is a generic macro which can work on all real floating-point types.
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It returns a non-zero value if the value of
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.I x
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has its sign bit set.
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.PP
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This is not the same as
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.IR "x < 0.0" ,
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because IEEE 754 floating point
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allows zero to be signed.
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2007-12-17 17:04:19 +00:00
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The comparison
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.IR "-0.0 < 0.0"
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is false, but
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.IR "signbit(\-0.0)"
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will return a non-zero value.
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.SH "CONFORMING TO"
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C99.
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This function is defined in IEC 559 (and the appendix with
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recommended functions in IEEE 754/IEEE 854).
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.SH "SEE ALSO"
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.BR copysign (3)
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