ilogb(3) — Linux manual page

```ilogb(3)                Library Functions Manual                ilogb(3)
```

NAME         top

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

LIBRARY         top

```       Math library (libm, -lm)
```

SYNOPSIS         top

```       #include <math.h>

int ilogb(double x);
int ilogbf(float x);
int ilogbl(long double x);

Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):

ilogb():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

ilogbf(), ilogbl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
```

DESCRIPTION         top

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

RETURN VALUE         top

```       On success, these functions return the exponent of x, as a signed
integer.

If x is zero, then a domain error occurs, and the functions
return FP_ILOGB0.

If x is a NaN, then a domain error occurs, and the functions
return FP_ILOGBNAN.

If x is negative infinity or positive infinity, then a domain
error occurs, and the functions return INT_MAX.
```

ERRORS         top

```       See math_error(7) for information on how to determine whether an
error has occurred when calling these functions.

The following errors can occur:

Domain error: x is 0 or a NaN
An invalid floating-point exception (FE_INVALID) is
raised, and errno is set to EDOM (but see BUGS).

Domain error: x is an infinity
An invalid floating-point exception (FE_INVALID) is
raised, and errno is set to EDOM (but see BUGS).
```

ATTRIBUTES         top

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

STANDARDS         top

```       C11, POSIX.1-2008.
```

HISTORY         top

```       C99, POSIX.1-2001.
```

BUGS         top

```       Before glibc 2.16, the following bugs existed in the glibc
implementation of these functions:

•  The domain error case where x is 0 or a NaN did not cause
errno to be set or (on some architectures) raise a floating-
point exception.

•  The domain error case where x is an infinity did not cause
errno to be set or raise a floating-point exception.
```

```       log(3), logb(3), significand(3)
```

COLOPHON         top

```       This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project.  Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.