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# remainder, remainderf, remainderl

From cppreference.com
< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
float remainderf( float x, float y ); | (1) | (since C99)
double remainder( double x, double y ); | (2) | (since C99)
long double remainderl( long double x, long double y ); | (3) | (since C99)
Defined in header `<tgmath.h>` |  |
#define remainder( x, y ) | (4) | (since C99)

1-3) Computes the IEEE remainder of the floating point division operation x/y.
4) Type-generic macro: If any argument has type long double, `remainderl` is called. Otherwise, if any argument has integer type or has type double, `remainder` is called. Otherwise, `remainderf` is called.

The IEEE floating-point remainder of the division operation x/y calculated by this function is exactly the value x - n*y, where the value `n` is the integral value nearest the exact value x/y. When |n-x/y| = ½, the value `n` is chosen to be even.

In contrast to fmod(), the returned value is not guaranteed to have the same sign as `x`.

If the returned value is `0`, it will have the same sign as `x`.

### [edit] Parameters

x, y | - | floating point values

### [edit] Return value

If successful, returns the IEEE 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 is returned.

If `y` is zero, but the domain error does not occur, zero 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),

- The current rounding mode has no effect.
- FE_INEXACT is never raised, the result is always exact.
- 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 either argument is NaN, NaN is returned

### [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.

### [edit] Example

Run this code

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

    #pragma STDC FENV_ACCESS ON
    int main(void)
    {
        printf("remainder(+5.1, +3.0) = %.1f\n", remainder(5.1,3));
        printf("remainder(-5.1, +3.0) = %.1f\n", remainder(-5.1,3));
        printf("remainder(+5.1, -3.0) = %.1f\n", remainder(5.1,-3));
        printf("remainder(-5.1, -3.0) = %.1f\n", remainder(-5.1,-3));

        // special values
        printf("remainder(-0.0, 1.0) = %.1f\n", remainder(-0.0, 1));
        printf("remainder(+5.1, Inf) = %.1f\n", remainder(5.1, INFINITY));

        // error handling
        feclearexcept(FE_ALL_EXCEPT);
        printf("remainder(+5.1, 0) = %.1f\n", remainder(5.1, 0));
        if(fetestexcept(FE_INVALID)) puts("    FE_INVALID raised");
    }

Output:

    remainder(+5.1, +3.0) = -0.9
    remainder(-5.1, +3.0) = 0.9
    remainder(+5.1, -3.0) = -0.9
    remainder(-5.1, -3.0) = 0.9
    remainder(+0.0, 1.0) = 0.0
    remainder(-0.0, 1.0) = -0.0
    remainder(+5.1, Inf) = 5.1
    remainder(+5.1, 0) = -nan
        FE_INVALID raised

### [edit] References

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.10.2 The remainder functions (p: 254-255)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.7.2 The remainder functions (p: 529)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.10.2 The remainder functions (p: 235)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.7.2 The remainder functions (p: 465)

### [edit] See also

div ldiv lldiv (C99) | computes quotient and remainder of integer division (function) [edit]
fmod fmodf fmodl (C99)(C99) | computes remainder of the floating-point division operation (function) [edit]
remquo remquof remquol (C99)(C99)(C99) | computes signed remainder as well as the three last bits of the division operation (function) [edit]
C++ documentation for remainder

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