man3/INFINITY.3

   1 .\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .TH INFINITY 3 (date) "Linux man-pages (unreleased)"
   6 .SH NAME
   7 INFINITY, NAN, HUGE_VAL, HUGE_VALF, HUGE_VALL \- floating-point constants
   8 .SH LIBRARY
   9 Math library
  10 .RI ( libm )
  11 .SH SYNOPSIS
  12 .nf
  13 .BR "#define _ISOC99_SOURCE" "      /* See feature_test_macros(7) */"
  14 .B #include <math.h>
  15 .PP
  16 .B INFINITY
  17 .PP
  18 .B NAN
  19 .PP
  20 .B HUGE_VAL
  21 .B HUGE_VALF
  22 .B HUGE_VALL
  23 .fi
  24 .SH DESCRIPTION
  25 The macro
  26 .B INFINITY
  27 expands to a
  28 .I float
  29 constant representing positive infinity.
  30 .PP
  31 The macro
  32 .B NAN
  33 expands to a
  34 .I float
  35 constant representing a quiet NaN
  36 (when supported).
  37 A
  38 .I quiet
  39 NaN is a NaN ("not-a-number") that does not raise exceptions
  40 when it is used in arithmetic.
  41 The opposite is a
  42 .I signaling
  43 NaN.
  44 See IEC 60559:1989.
  45 .PP
  46 The macros
  47 .BR HUGE_VAL ,
  48 .BR HUGE_VALF ,
  49 .B HUGE_VALL
  50 expand to constants of types
  51 .IR double ,
  52 .IR float ,
  53 and
  54 .IR "long double" ,
  55 respectively,
  56 that represent a large positive value, possibly positive infinity.
  57 .SH STANDARDS
  58 C99.
  59 .PP
  60 On a glibc system, the macro
  61 .B HUGE_VAL
  62 is always available.
  63 Availability of the
  64 .B NAN
  65 macro can be tested using
  66 .BR "#ifdef NAN" ,
  67 and similarly for
  68 .BR INFINITY ,
  69 .BR HUGE_VALF ,
  70 .BR HUGE_VALL .
  71 They will be defined by
  72 .I <math.h>
  73 if
  74 .B _ISOC99_SOURCE
  75 or
  76 .B _GNU_SOURCE
  77 is defined, or
  78 .B __STDC_VERSION__
  79 is defined
  80 and has a value not less than 199901L.
  81 .SH SEE ALSO
  82 .BR fpclassify (3),
  83 .BR math_error (7)