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27 .\" Inspired by a page by Walter Harms created 2002-08-10
29 .TH LOGB 3 2017-09-15 "" "Linux Programmer's Manual"
31 logb, logbf, logbl \- get exponent of a floating-point value
35 .BI "double logb(double " x );
37 .BI "float logbf(float " x );
39 .BI "long double logbl(long double " x );
44 Feature Test Macro Requirements for glibc (see
45 .BR feature_test_macros (7)):
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
61 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
62 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
63 || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
67 These functions extract the exponent from the
68 internal floating-point representation of
70 and return it as a floating-point value.
75 indicates the radix used for the system's floating-point representation.
81 .BI floor(log2( x ))\fR,
82 except that it is probably faster.
90 would have if it were normalized.
92 On success, these functions return the exponent of
102 is zero, then a pole error occurs, and the functions return
111 is negative infinity or positive infinity, then
112 positive infinity is returned.
116 for information on how to determine whether an error has occurred
117 when calling these functions.
119 The following errors can occur:
121 Pole error: \fIx\fP is 0
125 A divide-by-zero floating-point exception
129 These functions do not set
131 .\" FIXME . Is it intentional that these functions do not set errno?
132 .\" log(), log2(), log10() do set errno
133 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6793
138 .\" function occurs in 4.3BSD.
139 .\" see IEEE.3 in the 4.3BSD manual
141 For an explanation of the terms used in this section, see
147 Interface Attribute Value
152 T} Thread safety MT-Safe
155 C99, POSIX.1-2001, POSIX.1-2008.