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():

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.

The return value when y is zero is NaN. The return value when x is infinite is NaN. If the correct value would cause an underflow, a range error may occur, and the function returns either the correct result or 0.0.

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_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    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_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    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_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    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_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW);
    if(except_flags) {
        /* An error occurred; handle it appropriately. */
    }

    return EXIT_SUCCESS;
}

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

int main( void )
{

    return EXIT_SUCCESS;
}

produces the output:

0.500000
-0.500000
0.500000
-0.500000

Classification:

ANSI, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler No
Signal handler No
Thread Yes