man3/ilogb.3

   1 '\" t
   2 .\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
   3 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   4 .\"     <mtk.manpages@gmail.com>
   5 .\"
   6 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   7 .\"
   8 .\" Inspired by a page by Walter Harms created 2002-08-10
   9 .\"
  10 .TH ilogb 3 (date) "Linux man-pages (unreleased)"
  11 .SH NAME
  12 ilogb, ilogbf, ilogbl \- get integer exponent of a floating-point value
  13 .SH LIBRARY
  14 Math library
  15 .RI ( libm ", " \-lm )
  16 .SH SYNOPSIS
  17 .nf
  18 .B #include <math.h>
  19 .PP
  20 .BI "int ilogb(double " x );
  21 .BI "int ilogbf(float " x );
  22 .BI "int ilogbl(long double " x );
  23 .fi
  24 .PP
  25 .RS -4
  26 Feature Test Macro Requirements for glibc (see
  27 .BR feature_test_macros (7)):
  28 .RE
  29 .PP
  30 .BR ilogb ():
  31 .nf
  32     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  33         || _XOPEN_SOURCE >= 500
  34 .\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  35         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  36         || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  37 .fi
  38 .PP
  39 .BR ilogbf (),
  40 .BR ilogbl ():
  41 .nf
  42     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  43         || /* Since glibc 2.19: */ _DEFAULT_SOURCE
  44         || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
  45 .fi
  46 .SH DESCRIPTION
  47 These functions return the exponent part of their argument
  48 as a signed integer.
  49 When no error occurs, these functions
  50 are equivalent to the corresponding
  51 .BR logb (3)
  52 functions, cast to
  53 .IR int .
  54 .SH RETURN VALUE
  55 On success, these functions return the exponent of
  56 .IR x ,
  57 as a signed integer.
  58 .PP
  59 If
  60 .I x
  61 is zero, then a domain error occurs, and the functions return
  62 .\" the POSIX.1 spec for logb() says logb() gives pole error for this
  63 .\" case, but for ilogb() it says domain error.
  64 .BR FP_ILOGB0 .
  65 .\" glibc: The numeric value is either `INT_MIN' or `-INT_MAX'.
  66 .PP
  67 If
  68 .I x
  69 is a NaN, then a domain error occurs, and the functions return
  70 .BR FP_ILOGBNAN .
  71 .\" glibc: The numeric value is either `INT_MIN' or `INT_MAX'.
  72 .\" On i386, FP_ILOGB0 and FP_ILOGBNAN have the same value.
  73 .PP
  74 If
  75 .I x
  76 is negative infinity or positive infinity, then
  77 a domain error occurs, and the functions return
  78 .BR INT_MAX .
  79 .\"
  80 .\" POSIX.1-2001 also says:
  81 .\" If the correct value is greater than {INT_MAX}, {INT_MAX}
  82 .\" shall be returned and a domain error shall occur.
  83 .\"
  84 .\" If the correct value is less than {INT_MIN}, {INT_MIN}
  85 .\" shall be returned and a domain error shall occur.
  86 .SH ERRORS
  87 See
  88 .BR math_error (7)
  89 for information on how to determine whether an error has occurred
  90 when calling these functions.
  91 .PP
  92 The following errors can occur:
  93 .TP
  94 Domain error: \fIx\fP is 0 or a NaN
  95 An invalid floating-point exception
  96 .RB ( FE_INVALID )
  97 is raised, and
  98 .I errno
  99 is set to
 100 .B EDOM
 101 (but see BUGS).
 102 .TP
 103 Domain error: \fIx\fP is an infinity
 104 An invalid floating-point exception
 105 .RB ( FE_INVALID )
 106 is raised, and
 107 .I errno
 108 is set to
 109 .B EDOM
 110 (but see BUGS).
 111 .SH ATTRIBUTES
 112 For an explanation of the terms used in this section, see
 113 .BR attributes (7).
 114 .ad l
 115 .nh
 116 .TS
 117 allbox;
 118 lbx lb lb
 119 l l l.
 120 Interface       Attribute       Value
 121 T{
 122 .BR ilogb (),
 123 .BR ilogbf (),
 124 .BR ilogbl ()
 125 T}      Thread safety   MT-Safe
 126 .TE
 127 .hy
 128 .ad
 129 .sp 1
 130 .SH STANDARDS
 131 C11, POSIX.1-2008.
 132 .SH HISTORY
 133 C99, POSIX.1-2001.
 134 .SH BUGS
 135 .\" Bug raised: https://www.sourceware.org/bugzilla/show_bug.cgi?id=6794
 136 Before glibc 2.16, the following bugs existed in the
 137 glibc implementation of these functions:
 138 .IP \[bu] 3
 139 The domain error case where
 140 .I x
 141 is 0 or a NaN did not cause
 142 .I errno
 143 to be set or (on some architectures) raise a floating-point exception.
 144 .IP \[bu]
 145 The domain error case where
 146 .I x
 147 is an infinity did not cause
 148 .I errno
 149 to be set or raise a floating-point exception.
 150 .SH SEE ALSO
 151 .BR log (3),
 152 .BR logb (3),
 153 .BR significand (3)