logb(3) - c7

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():
20           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
21           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE ||
22           _POSIX_C_SOURCE >= 200112L;
23           or cc -std=c99
24       logbf(), logbl():
25           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
26           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
27           or cc -std=c99
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DESCRIPTION

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

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

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

63       C99, POSIX.1-2001.
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COLOPHON

69       This  page  is  part of release 3.53 of the Linux man-pages project.  A
70       description of the project, and information about reporting  bugs,  can
71       be found at http://www.kernel.org/doc/man-pages/.
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75                                  2010-09-20                           LOGB(3)