# 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.

# EXAMPLES

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

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

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

# 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`.