### NAME

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

### SYNOPSIS

**#include <math.h>**

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

Link with *-lm*.

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

**ilogb**(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE; or
*cc -std=c99* **ilogbf**(), **ilogbl**(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or
*cc -std=c99*

### DESCRIPTION

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

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

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.
| |

These functions do not set
errno for this case.
| |

Domain error: x is an infinity
| |

These functions do not set
errno or raise an exception for this case.
| |

### CONFORMING TO

C99, POSIX.1-2001.

### SEE ALSO

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

### COLOPHON

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