Defined in header `<cmath>` | ||
---|---|---|

(1) | ||

float fmod ( float x, float y ); | ||

float fmodf( float x, float y ); | (since C++11) | |

double fmod ( double x, double y ); | (2) | |

(3) | ||

long double fmod ( long double x, long double y ); | ||

long double fmodl( long double x, long double y ); | (since C++11) | |

Promoted fmod ( Arithmetic1 x, Arithmetic2 y ); | (4) | (since C++11) |

1-3) Computes the floating-point remainder of the division operation

`x/y`

.
4) A set of overloads or a function template for all combinations of arguments of arithmetic type not covered by (1-3). If any argument has integral type, it is cast to

`double`

. If any other argument is `long double`

, then the return type is `long double`

, otherwise it is `double`

.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 than `y`

in magnitude.

x, y | - | floating point values |

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.

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),

- If
`x`

is ±0 and`y`

is not zero, ±0 is returned - If
`x`

is ±∞ and`y`

is not NaN, NaN is returned and`FE_INVALID`

is raised - If
`y`

is ±0 and`x`

is not NaN, NaN is returned and`FE_INVALID`

is raised - If
`y`

is ±∞ and`x`

is finite,`x`

is returned. - If either argument is NaN, NaN is returned

POSIX requires that a domain error occurs if `x`

is infinite or `y`

is zero.

`std::fmod`

, but not `std::remainder`

is useful for doing silent wrapping of floating-point types to unsigned integer types: `(0.0 <= (y = std::fmod( std::rint(x), 65536.0 )) ? y : 65536.0 + y)`

is in the range `[-0.0 .. 65535.0]`

, which corresponds to `unsigned short`

, but `std::remainder(std::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 = std::remainder(std::fabs(x), (y = std::fabs(y))); if (std::signbit(result)) result += y; return std::copysign(result, x); }

The expression `x - trunc(x/y)*y`

may not equal `fmod(x,y)`

when the rounding of x/y to initialize the argument of trunc loses too much precision (example: x = 30.508474576271183309, y = 6.1016949152542370172).

#include <iostream> #include <cmath> #include <cfenv> #pragma STDC FENV_ACCESS ON int main() { std::cout << "fmod(+5.1, +3.0) = " << std::fmod(5.1,3) << '\n' << "fmod(-5.1, +3.0) = " << std::fmod(-5.1,3) << '\n' << "fmod(+5.1, -3.0) = " << std::fmod(5.1,-3) << '\n' << "fmod(-5.1, -3.0) = " << std::fmod(-5.1,-3) << '\n'; // special values std::cout << "fmod(+0.0, 1.0) = " << std::fmod(0, 1) << '\n' << "fmod(-0.0, 1.0) = " << std::fmod(-0.0, 1) << '\n' << "fmod(5.1, Inf) = " << std::fmod(5.1, INFINITY) << '\n'; // error handling std::feclearexcept(FE_ALL_EXCEPT); std::cout << "fmod(+5.1, 0) = " << std::fmod(5.1, 0) << '\n'; if(std::fetestexcept(FE_INVALID)) std::cout << " FE_INVALID raised\n"; }

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

(C++11) | computes quotient and remainder of integer division (function) |

(C++11)(C++11)(C++11) | signed remainder of the division operation (function) |

(C++11)(C++11)(C++11) | signed remainder as well as the three last bits of the division operation (function) |

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