fmod, fmodf, fmodl - cppreference.com (original) (raw)

Defined in header <math.h>
float fmodf( float x, float y ); (1) (since C99)
double fmod( double x, double y ); (2)
long double fmodl( long double x, long double y ); (3) (since C99)
Defined in header <tgmath.h>
#define fmod( x, y ) (4) (since C99)

1-3) Computes the floating-point remainder of the division operation x / y.

  1. Type-generic macro: If any argument has type long double, fmodl is called. Otherwise, if any argument has integer type or has type double, fmod is called. Otherwise, fmodf is called.

The floating-point remainder of the division operation x / y calculated by this function is exactly the value x - n * y, where n is x / y with its fractional part truncated.

The returned value has the same sign as x and is less or equal to y in magnitude.

Contents

[edit] Parameters

x, y - floating-point values

[edit] Return value

If successful, returns the floating-point remainder of the division x / y as defined above.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

[edit] Error handling

Errors are reported as specified in math_errhandling.

Domain error may occur if y is zero.

If the implementation supports IEEE floating-point arithmetic (IEC 60559):

[edit] Notes

POSIX requires that a domain error occurs if x is infinite or y is zero.

fmod, but not remainder is useful for doing silent wrapping of floating-point types to unsigned integer types: (0.0 <= (y = fmod(rint(x), 65536.0 )) ? y : 65536.0 + y) is in the range [-0.0, 65535.0], which corresponds to unsigned short, but remainder(rint(x), 65536.0) is in the range [-32767.0, +32768.0], which is outside of the range of signed short.

The double version of fmod behaves as if implemented as follows:

double fmod(double x, double y) { #pragma STDC FENV_ACCESS ON double result = remainder(fabs(x), (y = fabs(y))); if (signbit(result)) result += y; return copysign(result, x); }

[edit] Example

#include <fenv.h> #include <math.h> #include <stdio.h>   // #pragma STDC FENV_ACCESS ON   int main(void) { printf("fmod(+5.1, +3.0) = %.1f\n", fmod(5.1, 3)); printf("fmod(-5.1, +3.0) = %.1f\n", fmod(-5.1, 3)); printf("fmod(+5.1, -3.0) = %.1f\n", fmod(5.1, -3)); printf("fmod(-5.1, -3.0) = %.1f\n", fmod(-5.1, -3));   // special values printf("fmod(+0.0, 1.0) = %.1f\n", fmod(0, 1)); printf("fmod(-0.0, 1.0) = %.1f\n", fmod(-0.0, 1)); printf("fmod(+5.1, Inf) = %.1f\n", fmod(5.1, INFINITY));   // error handling feclearexcept(FE_ALL_EXCEPT); printf("fmod(+5.1, 0) = %.1f\n", fmod(5.1, 0)); if (fetestexcept(FE_INVALID)) puts(" FE_INVALID raised"); }

Possible output:

fmod(+5.1, +3.0) = 2.1 fmod(-5.1, +3.0) = -2.1 fmod(+5.1, -3.0) = 2.1 fmod(-5.1, -3.0) = -2.1 fmod(+0.0, 1.0) = 0.0 fmod(-0.0, 1.0) = -0.0 fmod(+5.1, Inf) = 5.1 fmod(+5.1, 0) = nan FE_INVALID raised

[edit] References

[edit] See also