logbl(3)

1LOGB(3)                    Linux Programmer's Manual                   LOGB(3)
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NAME

6       logb, logbf, logbl - get exponent of a floating-point value
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SYNOPSIS

9       #include <math.h>
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11       double logb(double x);
12       float logbf(float x);
13       long double logbl(long double x);
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15       Link with -lm.
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17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       logb(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
20       _ISOC99_SOURCE; or cc -std=c99
21       logbf(), logbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600
22       || _ISOC99_SOURCE; or cc -std=c99
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DESCRIPTION

25       These  functions  extract the exponent from the internal floating-point
26       representation of x and return it as a floating-point value.  The inte‐
27       ger  constant FLT_RADIX, defined in <float.h>, indicates the radix used
28       for the system's floating-point representation.   If  FLT_RADIX  is  2,
29       logb(x) is equal to floor(log2(x)), except that it is probably faster.
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31       If  x is subnormal, logb() returns the exponent x would have if it were
32       normalized.
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RETURN VALUE

35       On success, these functions return the exponent of x.
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37       If x is a NaN, a NaN is returned.
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39       If x is zero, then a  pole  error  occurs,  and  the  functions  return
40       -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.
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42       If  x is negative infinity or positive infinity, then positive infinity
43       is returned.
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ERRORS

46       See math_error(7) for information on how to determine whether an  error
47       has occurred when calling these functions.
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49       The following errors can occur:
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51       Pole error: x is 0
52              A  divide-by-zero  floating-point  exception  (FE_DIVBYZERO)  is
53              raised.
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55       These functions do not set errno.
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CONFORMING TO

58       C99, POSIX.1-2001.
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COLOPHON

64       This page is part of release 3.22 of the Linux  man-pages  project.   A
65       description  of  the project, and information about reporting bugs, can
66       be found at http://www.kernel.org/doc/man-pages/.
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70                                  2008-08-05                           LOGB(3)