Manpages - ilogb.3

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

  #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*():

      _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

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.

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.

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).

For an explanation of the terms used in this section, see *attributes*(7).

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

Before version 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)

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