man3/ilogb.3

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  27 .\" Inspired by a page by Walter Harms created 2002-08-10
  28 .\"
  29 .TH ILOGB 3 2017-09-15 "" "Linux Programmer's Manual"
  30 .SH NAME
  31 ilogb, ilogbf, ilogbl \- get integer exponent of a floating-point value
  32 .SH SYNOPSIS
  33 .B #include <math.h>
  34 .PP
  35 .BI "int ilogb(double " x );
  36 .br
  37 .BI "int ilogbf(float " x );
  38 .br
  39 .BI "int ilogbl(long double " x );
  40 .PP
  41 Link with \fI\-lm\fP.
  42 .PP
  43 .in -4n
  44 Feature Test Macro Requirements for glibc (see
  45 .BR feature_test_macros (7)):
  46 .in
  47 .PP
  48 .ad l
  49 .BR ilogb ():
  50 .RS 4
  51 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  52     || _XOPEN_SOURCE\ >=\ 500
  53 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  54     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  55     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  56 .RE
  57 .br
  58 .BR ilogbf (),
  59 .BR ilogbl ():
  60 .RS 4
  61 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  62     || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  63     || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  64 .RE
  65 .ad b
  66 .SH DESCRIPTION
  67 These functions return the exponent part of their argument
  68 as a signed integer.
  69 When no error occurs, these functions
  70 are equivalent to the corresponding
  71 .BR logb (3)
  72 functions, cast to
  73 .IR int .
  74 .SH RETURN VALUE
  75 On success, these functions return the exponent of
  76 .IR x ,
  77 as a signed integer.
  78 .PP
  79 If
  80 .I x
  81 is zero, then a domain error occurs, and the functions return
  82 .\" the POSIX.1 spec for logb() says logb() gives pole error for this
  83 .\" case, but for ilogb() it says domain error.
  84 .BR FP_ILOGB0 .
  85 .\" glibc: The numeric value is either `INT_MIN' or `-INT_MAX'.
  86 .PP
  87 If
  88 .I x
  89 is a NaN, then a domain error occurs, and the functions return
  90 .BR FP_ILOGBNAN .
  91 .\" glibc: The numeric value is either `INT_MIN' or `INT_MAX'.
  92 .\" On i386, FP_ILOGB0 and FP_ILOGBNAN have the same value.
  93 .PP
  94 If
  95 .I x
  96 is negative infinity or positive infinity, then
  97 a domain error occurs, and the functions return
  98 .BR INT_MAX .
  99 .\"
 100 .\" POSIX.1-2001 also says:
 101 .\" If the correct value is greater than {INT_MAX}, {INT_MAX}
 102 .\" shall be returned and a domain error shall occur.
 103 .\"
 104 .\" If the correct value is less than {INT_MIN}, {INT_MIN}
 105 .\" shall be returned and a domain error shall occur.
 106 .SH ERRORS
 107 See
 108 .BR math_error (7)
 109 for information on how to determine whether an error has occurred
 110 when calling these functions.
 111 .PP
 112 The following errors can occur:
 113 .TP
 114 Domain error: \fIx\fP is 0 or a NaN
 115 An invalid floating-point exception
 116 .RB ( FE_INVALID )
 117 is raised, and
 118 .I errno
 119 is set to
 120 .BR EDOM
 121 (but see BUGS).
 122 .IP
 123 .TP
 124 Domain error: \fIx\fP is an infinity
 125 An invalid floating-point exception
 126 .RB ( FE_INVALID )
 127 is raised, and
 128 .I errno
 129 is set to
 130 .BR EDOM
 131 (but see BUGS).
 132 .SH ATTRIBUTES
 133 For an explanation of the terms used in this section, see
 134 .BR attributes (7).
 135 .TS
 136 allbox;
 137 lbw27 lb lb
 138 l l l.
 139 Interface       Attribute       Value
 140 T{
 141 .BR ilogb (),
 142 .BR ilogbf (),
 143 .BR ilogbl ()
 144 T}      Thread safety   MT-Safe
 145 .TE
 146 .SH CONFORMING TO
 147 C99, POSIX.1-2001, POSIX.1-2008.
 148 .SH BUGS
 149 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6794
 150 Before version 2.16, the following bugs existed in the
 151 glibc implementation of these functions:
 152 .IP * 3
 153 The domain error case where
 154 .I x
 155 is 0 or a NaN did not cause
 156 .I errno
 157 to be set or (on some architectures) raise a floating-point exception.
 158 .IP * 3
 159 The domain error case where
 160 .I x
 161 is an infinity did not cause
 162 .I errno
 163 to be set or raise a floating-point exception.
 164 .SH SEE ALSO
 165 .BR log (3),
 166 .BR logb (3),
 167 .BR significand (3)