1 .\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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25 .\" Inspired by a page by Walter Harms created 2002-08-10
27 .TH LOGB 3 2008-08-05 "" "Linux Programmer's Manual"
29 logb, logbf, logbl \- get exponent of a floating-point value
33 .BI "double logb(double " x );
35 .BI "float logbf(float " x );
37 .BI "long double logbl(long double " x );
42 Feature Test Macro Requirements for glibc (see
43 .BR feature_test_macros (7)):
48 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE; or
53 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
57 These functions extract the exponent from the
58 internal floating-point representation of
60 and return it as a floating-point value.
65 indicates the radix used for the system's floating-point representation.
71 .BI floor(log2( x ))\fR,
72 except that it is probably faster.
80 would have if it were normalized.
82 On success, these functions return the exponent of
92 is zero, then a pole error occurs, and the functions return
101 is negative infinity or positive infinity, then
102 positive infinity is returned.
106 for information on how to determine whether an error has occurred
107 when calling these functions.
109 The following errors can occur:
111 Pole error: \fIx\fP is 0
115 A divide-by-zero floating-point exception
119 These functions do not set
121 .\" FIXME . Is it intentional that these functions do not set errno?
122 .\" log(), log2(), log10() do set errno
123 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6793
128 .\" function occurs in 4.3BSD.
129 .\" see IEEE.3 in the 4.3BSD manual