man3/INFINITY.3

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  25 .TH INFINITY 3  2017-09-15 "" "Linux Programmer's Manual"
  26 .SH NAME
  27 INFINITY, NAN, HUGE_VAL, HUGE_VALF, HUGE_VALL \- floating-point constants
  28 .SH SYNOPSIS
  29 .nf
  30 .BR "#define _ISOC99_SOURCE" "      /* See feature_test_macros(7) */"
  31 .B #include <math.h>
  32 .PP
  33 .B INFINITY
  34 .PP
  35 .B NAN
  36 .PP
  37 .B HUGE_VAL
  38 .B HUGE_VALF
  39 .B HUGE_VALL
  40 .fi
  41 .SH DESCRIPTION
  42 The macro
  43 .B INFINITY
  44 expands to a
  45 .I float
  46 constant representing positive infinity.
  47 .PP
  48 The macro
  49 .B NAN
  50 expands to a
  51 .I float
  52 constant representing a quiet NaN
  53 (when supported).
  54 A
  55 .I quiet
  56 NaN is a NaN ("not-a-number") that does not raise exceptions
  57 when it is used in arithmetic.
  58 The opposite is a
  59 .I signaling
  60 NaN.
  61 See IEC 60559:1989.
  62 .PP
  63 The macros
  64 .BR HUGE_VAL ,
  65 .BR HUGE_VALF ,
  66 .B HUGE_VALL
  67 expand to constants of types
  68 .IR double ,
  69 .I float
  70 and
  71 .IR "long double" ,
  72 respectively,
  73 that represent a large positive value, possibly positive infinity.
  74 .SH CONFORMING TO
  75 C99.
  76 .SH AVAILABILITY
  77 On a glibc system, the macro
  78 .B HUGE_VAL
  79 is always available.
  80 Availability of the
  81 .B NAN
  82 macro can be tested using
  83 .BR "#ifdef NAN" ,
  84 and similarly for
  85 .BR INFINITY ,
  86 .BR HUGE_VALF ,
  87 .BR HUGE_VALL .
  88 They will be defined by
  89 .I <math.h>
  90 if
  91 .B _ISOC99_SOURCE
  92 or
  93 .B _GNU_SOURCE
  94 is defined, or
  95 .B __STDC_VERSION__
  96 is defined
  97 and has a value not less than 199901L.
  98 .SH SEE ALSO
  99 .BR fpclassify (3),
 100 .BR math_error (7)