man-pages/man3/INFINITY.3

.\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
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.TH INFINITY 3  2007-07-26 "" "Linux Programmer's Manual"
.SH NAME
INFINITY, NAN, HUGE_VAL, HUGE_VALF, HUGE_VALL \- floating-point constants
.SH SYNOPSIS
.nf
.B #define _ISOC99_SOURCE
.br
.B #include <math.h>
.sp
.B INFINITY
.sp
.B NAN
.sp
.B HUGE_VAL
.br
.B HUGE_VALF
.br
.B HUGE_VALL
.fi
.SH DESCRIPTION
The macro
.B INFINITY
expands to a \fIfloat\fP constant representing positive infinity.

The macro
.B NAN
expands to a \fIfloat\fP constant representing a quiet NaN
(when supported).
A
.I quiet
NaN is a NaN ("not-a-number") that does not raise exceptions
when it is used in arithmetic.
The opposite is a
.I signaling
NaN.
See IEC 60559:1989.

The macros
.BR HUGE_VAL ,
.BR HUGE_VALF ,
.B HUGE_VALL
expand to constants of types \fIdouble\fP, \fIfloat\fP
and \fIlong double\fP, respectively,
that represent a large positive value, possibly plus infinity.
.SH "CONFORMING TO"
C99.
.SH AVAILABILITY
On a glibc system, the macro
.B HUGE_VAL
is always available.
Availability of the
.B NAN
macro can be tested using
.BR "#ifdef NAN" ,
and similarly for
.BR INFINITY ,
.BR HUGE_VALF ,
.BR HUGE_VALL .
They will be defined by
.I <math.h>
if
.B _ISOC99_SOURCE
or
.B _GNU_SOURCE
is defined, or
.B __STDC_VERSION__
is defined
and has a value not less than 199901L.
.SH "SEE ALSO"
.BR fpclassify (3),
.BR feature_test_macros (7),
.BR math_error (7)