ilogb(3) - Linux manual page (original) (raw)


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)](../man3/logb.3.html) 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)](../man7/math%5Ferror.7.html) 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](../man3/errno.3.html)_ is set to **EDOM** (but see BUGS).

   Domain error: _x_ is an infinity
          An invalid floating-point exception (**FE_INVALID**) is raised,
          and _[errno](../man3/errno.3.html)_ is set to **EDOM** (but see BUGS).

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **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](../man3/errno.3.html)_
      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](../man3/errno.3.html)_ to be set or raise a floating-point exception.

SEE ALSO top

   [log(3)](../man3/log.3.html), [logb(3)](../man3/logb.3.html), [significand(3)](../man3/significand.3.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 ilogb(3)


Pages that refer to this page:logb(3), significand(3)