rint, rintf, rintl, lrint, lrintf, lrintl, llrint, llrintf, llrintl - cppreference.com

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# rint, rintf, rintl, lrint, lrintf, lrintl, llrint, llrintf, llrintl

From cppreference.com
< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
float rintf( float arg ); | (1) | (since C99)
double rint( double arg ); | (2) | (since C99)
long double rintl( long double arg ); | (3) | (since C99)
Defined in header `<tgmath.h>` |  |
#define rint( arg ) | (4) | (since C99)
Defined in header `<math.h>` |  |
long lrintf( float arg ); | (5) | (since C99)
long lrint( double arg ); | (6) | (since C99)
long lrintl( long double arg ); | (7) | (since C99)
Defined in header `<tgmath.h>` |  |
#define lrint( arg ) | (8) | (since C99)
Defined in header `<math.h>` |  |
long long llrintf( float arg ); | (9) | (since C99)
long long llrint( double arg ); | (10) | (since C99)
long long llrintl( long double arg ); | (11) | (since C99)
Defined in header `<tgmath.h>` |  |
#define llrint( arg ) | (12) | (since C99)

1-3) Rounds the floating-point argument `arg` to an integer value in floating-point format, using the current rounding mode.
5-7, 9-11) Rounds the floating-point argument `arg` to an integer value in integer format, using the current rounding mode.
4,8,12) Type-generic macros: If `arg` has type long double, `rintl`, `lrintl`, `llrintl` is called. Otherwise, if `arg` has integer type or the type double, `rint`, `lrint`, `llrint` is called. Otherwise, `rintf`, `lrintf`, `llrintf` is called, respectively.

### [edit] Parameters

arg | - | floating point value

### [edit] Return value

If no errors occur, the nearest integer value to `arg`, according to the current rounding mode, is returned.

### [edit] Error handling

Errors are reported as specified in math_errhandling

If the result of `lrint` or `llrint` is outside the range representable by the return type, a domain error or a range error may occur.

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

  For the `rint` function:

- If `arg` is ±∞, it is returned, unmodified
- If `arg` is ±0, it is returned, unmodified
- If `arg` is NaN, NaN is returned

  For `lrint` and `llrint` functions:

- If `arg` is ±∞, FE_INVALID is raised and an implementation-defined value is returned
- If the result of the rounding is outside the range of the return type, FE_INVALID is raised and an implementation-defined value is returned
- If `arg` is NaN, FE_INVALID is raised and an implementation-defined value is returned

### [edit] Notes

POSIX specifies that all cases where `lrint` or `llrint` raise FE_INEXACT are domain errors.

As specified in math_errhandling, FE_INEXACT may be (but isn't required to be on non-IEEE floating-point platforms) raised by `rint` when rounding a non-integer finite value.

The only difference between `rint` and nearbyint is that nearbyint never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard floating-point formats, so `rint` never overflows on its own; however the result may overflow any integer type (including intmax_t), when stored in an integer variable.

If the current rounding mode is...

- FE_DOWNWARD, then `rint` is equivalent to floor.
- FE_UPWARD, then `rint` is equivalent to ceil.
- FE_TOWARDZERO, then `rint` is equivalent to trunc
- FE_TONEAREST, then `rint` differs from round in that halfway cases are rounded to even rather than away from zero.

### [edit] Example

Run this code

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

    int main(void)
    {
    #pragma STDC FENV_ACCESS ON
        fesetround(FE_TONEAREST);
        printf("rounding to nearest:\nrint(+2.3) = %+.1f  ", rint(2.3));
        printf("rint(+2.5) = %+.1f  ", rint(2.5));
        printf("rint(+3.5) = %+.1f\n", rint(3.5));
        printf("rint(-2.3) = %+.1f  ", rint(-2.3));
        printf("rint(-2.5) = %+.1f  ", rint(-2.5));
        printf("rint(-3.5) = %+.1f\n", rint(-3.5));

        fesetround(FE_DOWNWARD);
        printf("rounding down: \nrint(+2.3) = %+.1f  ", rint(2.3));
        printf("rint(+2.5) = %+.1f  ", rint(2.5));
        printf("rint(+3.5) = %+.1f\n", rint(3.5));
        printf("rint(-2.3) = %+.1f  ", rint(-2.3));
        printf("rint(-2.5) = %+.1f  ", rint(-2.5));
        printf("rint(-3.5) = %+.1f\n", rint(-3.5));
        printf("rounding down with lrint: \nlrint(+2.3) = %ld  ", lrint(2.3));
        printf("lrint(+2.5) = %ld  ", lrint(2.5));
        printf("lrint(+3.5) = %ld\n", lrint(3.5));
        printf("lrint(-2.3) = %ld  ", lrint(-2.3));
        printf("lrint(-2.5) = %ld  ", lrint(-2.5));
        printf("lrint(-3.5) = %ld\n", lrint(-3.5));

        printf("lrint(-0.0) = %ld\n", lrint(-0.0));
        printf("lrint(-Inf) = %ld\n", lrint(-INFINITY)); // FE_INVALID raised

        // error handling
        feclearexcept(FE_ALL_EXCEPT);
        printf("rint(1.1) = %.1f\n", rint(1.1));
        if(fetestexcept(FE_INEXACT)) puts("    FE_INEXACT was raised");

        feclearexcept(FE_ALL_EXCEPT);
        printf("lrint(LONG_MIN-2048.0) = %ld\n", lrint(LONG_MIN-2048.0));
        if(fetestexcept(FE_INVALID)) puts("    FE_INVALID was raised");
    }

Possible output:

    rounding to nearest:
    rint(+2.3) = +2.0  rint(+2.5) = +2.0  rint(+3.5) = +4.0
    rint(-2.3) = -2.0  rint(-2.5) = -2.0  rint(-3.5) = -4.0
    rounding down:
    rint(+2.3) = +2.0  rint(+2.5) = +2.0  rint(+3.5) = +3.0
    rint(-2.3) = -3.0  rint(-2.5) = -3.0  rint(-3.5) = -4.0
    rounding down with lrint:
    lrint(+2.3) = 2  lrint(+2.5) = 2  lrint(+3.5) = 3
    lrint(-2.3) = -3  lrint(-2.5) = -3  lrint(-3.5) = -4
    lrint(-0.0) = 0
    lrint(-Inf) = -9223372036854775808
    rint(1.1) = 1.0
        FE_INEXACT was raised
    lrint(LONG_MIN-2048.0) = -9223372036854775808
        FE_INVALID was raised

### [edit] See also

trunctruncftruncl (C99)(C99)(C99) | rounds to nearest integer not greater in magnitude than the given value (function) [edit]
nearbyintnearbyintfnearbyintl (C99)(C99)(C99) | rounds to an integer using current rounding mode (function) [edit]
fegetroundfesetround (C99)(C99) | gets or sets rounding direction (function) [edit]
C++ documentation for rint

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