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

fmod(3) Library Functions Manual fmod(3)

NAME top

   fmod, fmodf, fmodl - floating-point remainder function

LIBRARY top

   Math library (_libm_, _-lm_)

SYNOPSIS top

   **#include <math.h>**

   **double fmod(double** _x_**, double** _y_**);**
   **float fmodf(float** _x_**, float** _y_**);**
   **long double fmodl(long double** _x_**, long double** _y_**);**

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

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

DESCRIPTION top

   These functions compute the floating-point remainder of dividing _x_
   by _y_.  The return value is _x_ - _n_ * _y_, where _n_ is the quotient of _x_
   / _y_, rounded toward zero to an integer.

   To obtain the modulus, more specifically, the Least Positive
   Residue, you will need to adjust the result from **fmod**() like so:

       z = fmod(x, y);
       if (z < 0)
            z += fabs(y);

   An alternate way to express this is with _fmod(fmod(x, y) + y, y)_,
   but the second **fmod**() usually costs way more than the one branch.

RETURN VALUE top

   On success, these functions return the value _x_ - _n_*_y_, for some
   integer _n_, such that the returned value has the same sign as _x_ and
   a magnitude less than the magnitude of _y_.

   If _x_ or _y_ is a NaN, a NaN is returned.

   If _x_ is an infinity, a domain error occurs, and a NaN is returned.

   If _y_ is zero, a domain error occurs, and a NaN is returned.

   If _x_ is +0 (-0), and _y_ is not zero, +0 (-0) is returned.

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

   Domain error: _y_ is zero
          _[errno](../man3/errno.3.html)_ is set to **EDOM**.  An invalid floating-point exception
          (**FE_INVALID**) is raised.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **fmod**(), **fmodf**(), **fmodl**()             │ Thread safety │ MT-Safe │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   C11, POSIX.1-2008.

HISTORY top

   C99, POSIX.1-2001.

   The variant returning _double_ also conforms to SVr4, 4.3BSD, C89.

BUGS top

   Before glibc 2.10, the glibc implementation did not set _[errno](../man3/errno.3.html)_ to
   **EDOM** when a domain error occurred for an infinite _x_.

EXAMPLES top

   The call _fmod(372, 360)_ returns 12.

   The call _fmod(-372, 360)_ returns -12.

   The call _fmod(-372, -360)_ also returns -12.

SEE ALSO top

   [remainder(3)](../man3/remainder.3.html)

COLOPHON top

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Linux man-pages 6.10 2024-11-17 fmod(3)

Pages that refer to this page:remainder(3), remquo(3)