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

6       ilogb, ilogbf, ilogbl - get integer exponent of a floating-point value
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SYNOPSIS

9       #include <math.h>
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11       int ilogb(double x);
12       int ilogbf(float x);
13       int ilogbl(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       ilogb():
20           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
21               || _XOPEN_SOURCE >= 500
22               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
23               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
24       ilogbf(), ilogbl():
25           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
26               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
27               || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

30       These  functions return the exponent part of their argument as a signed
31       integer.  When no error occurs, these functions are equivalent  to  the
32       corresponding logb(3) functions, cast to int.
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RETURN VALUE

35       On success, these functions return the exponent of x, as a signed inte‐
36       ger.
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38       If x is zero, then a domain error  occurs,  and  the  functions  return
39       FP_ILOGB0.
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41       If  x  is  a  NaN, then a domain error occurs, and the functions return
42       FP_ILOGBNAN.
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44       If x is negative infinity or positive infinity,  then  a  domain  error
45       occurs, and the functions return INT_MAX.
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ERRORS

48       See  math_error(7) for information on how to determine whether an error
49       has occurred when calling these functions.
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51       The following errors can occur:
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53       Domain error: x is 0 or a NaN
54              An invalid floating-point exception (FE_INVALID) is raised,  and
55              errno is set to EDOM (but see BUGS).
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57       Domain error: x is an infinity
58              An  invalid floating-point exception (FE_INVALID) is raised, and
59              errno is set to EDOM (but see BUGS).
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ATTRIBUTES

62       For  an  explanation  of  the  terms  used   in   this   section,   see
63       attributes(7).
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65       ┌────────────────────────────┬───────────────┬─────────┐
66       │Interface                   │ Attribute     │ Value   │
67       ├────────────────────────────┼───────────────┼─────────┤
68       │ilogb(), ilogbf(), ilogbl() │ Thread safety │ MT-Safe │
69       └────────────────────────────┴───────────────┴─────────┘

CONFORMING TO

71       C99, POSIX.1-2001, POSIX.1-2008.
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BUGS

74       Before  version 2.16, the following bugs existed in the glibc implemen‐
75       tation of these functions:
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77       *  The domain error case where x is 0 or a NaN did not cause  errno  to
78          be set or (on some architectures) raise a floating-point exception.
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80       *  The  domain error case where x is an infinity did not cause errno to
81          be set or raise a floating-point exception.
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SEE ALSO

84       log(3), logb(3), significand(3)
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COLOPHON

87       This page is part of release 4.15 of the Linux  man-pages  project.   A
88       description  of  the project, information about reporting bugs, and the
89       latest    version    of    this    page,    can     be     found     at
90       https://www.kernel.org/doc/man-pages/.
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94                                  2017-09-15                          ILOGB(3)
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