| 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. |
NAME
fmod, fmodf, fmodl - floating-point remainder function
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>double fmod(double \nx\n, double \ny\n);\n
\nfloat fmodf(float \nx\n, float \ny\n);\n
\nlong double fmodl(long double \nx\n, long double \ny\n);fmodf(), fmodl():
\n
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
\n
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
\n
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCEDESCRIPTION
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)