fmodf - floating-point remainder function

NAME LIBRARY SYNOPSIS DESCRIPTION RETURN VALUE ERRORS ATTRIBUTES STANDARDS HISTORY BUGS EXAMPLES SEE ALSO

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 += 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

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.

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