ilogbf(3)

1ilogb(3)                   Library Functions Manual                   ilogb(3)
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NAME

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

9       Math library (libm, -lm)
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SYNOPSIS

12       #include <math.h>
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14       int ilogb(double x);
15       int ilogbf(float x);
16       int ilogbl(long double x);
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18   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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20       ilogb():
21           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
22               || _XOPEN_SOURCE >= 500
23               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
24               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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26       ilogbf(), ilogbl():
27           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
28               || /* Since glibc 2.19: */ _DEFAULT_SOURCE
29               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

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

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

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

64       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
65       tributes(7).
66
67       ┌────────────────────────────────────────────┬───────────────┬─────────┐
68       │Interface                                   │ Attribute     │ Value   │
69       ├────────────────────────────────────────────┼───────────────┼─────────┤
70       │ilogb(), ilogbf(), ilogbl()                 │ Thread safety │ MT-Safe │
71       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

74       C11, POSIX.1-2008.
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HISTORY

77       C99, POSIX.1-2001.
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BUGS

80       Before   glibc   2.16,   the   following  bugs  existed  in  the  glibc
81       implementation of these functions:
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83       •  The domain error case where x is 0 or a NaN did not cause  errno  to
84          be set or (on some architectures) raise a floating-point exception.
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86       •  The  domain error case where x is an infinity did not cause errno to
87          be set or raise a floating-point exception.
88