Compute a residue, using floating-point modular arithmetic
#include <math.h> double fmod( double x, double y ); float fmodf( float x, float y ); long double fmodl( long double x, long double y );
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:
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.
#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
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | No |
Signal handler | No |
Thread | Yes |