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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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25       ilogbf(), ilogbl():
26           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
27               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
28               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

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

36       On success, these functions return the exponent of x, as a signed inte‐
37       ger.
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39       If x is zero, then a domain error  occurs,  and  the  functions  return
40       FP_ILOGB0.
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42       If  x  is  a  NaN, then a domain error occurs, and the functions return
43       FP_ILOGBNAN.
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45       If x is negative infinity or positive infinity, then a domain error oc‐
46       curs, and the functions return INT_MAX.
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ERRORS

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

63       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
64       tributes(7).
65
66       ┌────────────────────────────────────────────┬───────────────┬─────────┐
67       │Interface                                   │ Attribute     │ Value   │
68       ├────────────────────────────────────────────┼───────────────┼─────────┤
69       │ilogb(), ilogbf(), ilogbl()                 │ Thread safety │ MT-Safe │
70       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

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

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

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

89       This page is part of release 5.13 of the Linux  man-pages  project.   A
90       description  of  the project, information about reporting bugs, and the
91       latest    version    of    this    page,    can     be     found     at
92       https://www.kernel.org/doc/man-pages/.
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96                                  2021-03-22                          ILOGB(3)
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