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.

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.

For a correct value that would cause an underflow, these functions return 0.0. The return value when y is zero is NaN. The return value when x is infinite is NaN.

If an error occurs, these functions return 0, but this is also a valid mathematical result. If you want to check for errors, set errno to 0, call the function, and then check errno again. These functions don't change errno if no errors occurred.

Examples:

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

int main( void )
{
    printf( "%f\n", fmod(  4.5,  2.0 ) );
    printf( "%f\n", fmod( -4.5,  2.0 ) );
    printf( "%f\n", fmod(  4.5, -2.0 ) );
    printf( "%f\n", fmod( -4.5, -2.0 ) );

    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

Related links