# fmod(), fmodf(), fmodl()

Compute a residue, using floating-point modular arithmetic

## 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 );
```

## Arguments:

x
An arbitrary number.
y
The modulus.

## Library:

libm

Use the -l m option to qcc to link against this library.

## Description:

The fmod() and fmodf() functions compute the floating-point residue of x (mod y), which is the remainder of x / y, even if the quotient x / y isn't representable.

To check for error situations, use feclearexcept() and fetestexcept(). For example:

• Call feclearexcept(FE_ALL_EXCEPT) before calling fmod(), fmodf(), or fmodl().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

## Returns:

The residue, x - (i × y), for some integer i such that, if y is nonzero, the result has the same sign as x and a magnitude less than the magnitude of y.

If: These functions return: Errors:
x is Inf NaN FE_INVALID
y is 0.0 NaN FE_INVALID
x or y is NaN NaN
The correct value would cause underflow 0.0

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

## Examples:

```#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
int except_flags;

feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod(  4.5,  2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod( -4.5,  2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod(  4.5, -2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

feclearexcept(FE_ALL_EXCEPT);
printf( "%f\n", fmod( -4.5, -2.0 ) );
except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

return EXIT_SUCCESS;
}
```

produces the output:

```0.500000
-0.500000
0.500000
-0.500000
```

## Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No