mirror of https://github.com/mkerrisk/man-pages
57 lines
1.3 KiB
Groff
57 lines
1.3 KiB
Groff
.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
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.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\" Distributed under GPL
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.\" Based on glibc infopages
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.TH SIGNBIT 3 2008-08-05 "GNU" "Linux Programmer's Manual"
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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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Link with \fI\-lm\fP.
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.BR signbit ():
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_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.ad b
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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 allows zero to be signed.
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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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NaNs and infinities have a sign bit.
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.SH RETURN VALUE
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The
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.BR signbit ()
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macro returns non-zero if the sign of
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.I x
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is negative; otherwise it returns zero.
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.SH ERRORS
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No errors occur.
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.SH "CONFORMING TO"
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C99, POSIX.1-2001.
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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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