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27 .\" Inspired by a page by Walter Harms created 2002-08-10
29 .TH LOGB 3 2014-02-28 "" "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 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
52 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
53 _POSIX_C_SOURCE\ >=\ 200112L;
62 _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
63 _POSIX_C_SOURCE\ >=\ 200112L;
70 These functions extract the exponent from the
71 internal floating-point representation of
73 and return it as a floating-point value.
78 indicates the radix used for the system's floating-point representation.
84 .BI floor(log2( x ))\fR,
85 except that it is probably faster.
93 would have if it were normalized.
95 On success, these functions return the exponent of
105 is zero, then a pole error occurs, and the functions return
114 is negative infinity or positive infinity, then
115 positive infinity is returned.
119 for information on how to determine whether an error has occurred
120 when calling these functions.
122 The following errors can occur:
124 Pole error: \fIx\fP is 0
128 A divide-by-zero floating-point exception
132 These functions do not set
134 .\" FIXME . Is it intentional that these functions do not set errno?
135 .\" log(), log2(), log10() do set errno
136 .\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6793
141 .\" function occurs in 4.3BSD.
142 .\" see IEEE.3 in the 4.3BSD manual
144 .SS Multithreading (see pthreads(7))
150 functions are thread-safe.