.\" Copyright 2002 Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\" Distributed under GPL, 2002-07-27 Walter Harms
.\" This was done with the help of the glibc manual.
.\"
.\" 2004-10-31, aeb, corrected
.TH FPCLASSIFY 3  2007-07-26 "" "Linux Programmer's Manual"
.SH NAME
fpclassify, isfinite, isnormal, isnan, isinf \- floating-point
classification macros
.SH SYNOPSIS
.nf
.B #include <math.h>
.sp
.BI "int fpclassify(" x );
.sp
.BI "int isfinite(" x );
.sp
.BI "int isnormal(" x );
.sp
.BI "int isnan(" x );
.sp
.BI "int isinf(" x );
.fi
.sp
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.\" I haven't fully grokked the source to determine the FTM requirements;
.\" in part, the following has been tested by experiment.
.ad l
.BR fpclassify (),
.BR isfinite (),
.BR isnormal ():
_XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
.I cc\ -std=c99
.br
.BR isnan ():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or
.I cc\ -std=c99
.br
.BR isinf ():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
.I cc\ -std=c99
.ad b
.SH DESCRIPTION
Floating point numbers can have special values, such as
infinite or NaN.
With the macro
.BI fpclassify( x )
you can find out what type
.I x
is.
The macro takes any floating-point expression as argument.
The result is one of the following values:
.TP
.B FP_NAN
.I x
is "Not a Number".
.TP
.B FP_INFINITE
.I x
is either plus or minus infinity.
.TP
.B FP_ZERO
.I x
is zero.
.TP
.B FP_SUBNORMAL
.I x
is too small to be represented in normalized format.
.TP
.B FP_NORMAL
if nothing of the above is correct then it must be a
normal floating-point number.
.LP
The other macros provide a short answer to some standard questions.
.TP
.BI isfinite( x )
returns a non-zero value if
.br
(fpclassify(x) != FP_NAN && fpclassify(x) != FP_INFINITE)
.TP
.BI isnormal( x )
returns a non-zero value if
(fpclassify(x) == FP_NORMAL)
.TP
.BI isnan( x )
returns a non-zero value if
(fpclassify(x) == FP_NAN)
.TP
.BI isinf( x )
returns 1 if
.I x
is positive infinity, and \-1 if
.I x
is negative infinity.
.SH "CONFORMING TO"
C99
.SH NOTES
In glibc 2.01 and earlier,
.BR isinf ()
returns a non-zero value (actually: 1) if
.I x
is an infinity (positive or negative).
(This is all that C99 requires.)
.SH "SEE ALSO"
.BR finite (3),
.BR INFINITY (3),
.BR isgreater (3)