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) |
x/y
.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),
x
is ±0 and y
is not zero, ±0 is returned x
is ±∞ and y
is not NaN, NaN is returned and FE_INVALID
is raised y
is ±0 and x
is not NaN, NaN is returned and FE_INVALID
is raised y
is ±∞ and x
is finite, x
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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