fmod(3)                    Library Functions Manual                    fmod(3)

NAME
       fmod, fmodf, fmodl - floating-point remainder function

LIBRARY
       Math library (libm, -lm)

SYNOPSIS
       #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
       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 += 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
       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
       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 an infinity
              errno is set to EDOM (but see BUGS).  An invalid floating-point
              exception (FE_INVALID) is raised.

       Domain error: y is zero
              errno is set to EDOM.  An invalid floating-point exception
              (FE_INVALID) is raised.

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

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |fmod (), fmodf (), fmodl ()                 | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       C99, POSIX.1-2001.

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

BUGS
       Before glibc 2.10, the glibc implementation did not set errno to EDOM
       when a domain error occurred for an infinite x.

EXAMPLES
       The call fmod(372, 360) returns 348.

       The call fmod(-372, 360) returns -12.

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

SEE ALSO
       remainder(3)

Linux man-pages 6.7               2023-10-31                           fmod(3)