rint

float rintf( float arg );

double rint( double arg );

long double rintl( long double arg );

#define rint( arg )

long lrintf( float arg );

long lrint( double arg );

long lrintl( long double arg );

#define lrint( arg )

long long llrintf( float arg );

long long llrint( double arg );

long long llrintl( long double arg );

#define llrint( arg )

Parameters

Return value

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

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

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.

Example

#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 (halfway cases to even):\n"
           "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("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");
}

rounding to nearest (halfway cases to even):
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

References

• C11 standard (ISO/IEC 9899:2011):
  • 7.12.9.4 The rint functions (p: 252)
  • 7.12.9.5 The lrint and llrint functions (p: 252)
  • 7.25 Type-generic math <tgmath.h> (p: 373-375)
  • F.10.6.4 The rint functions (p: 527)
  • F.10.6.5 The lrint and llrint functions (p: 527)
• C99 standard (ISO/IEC 9899:1999):
  • 7.12.9.4 The rint functions (p: 232-233)
  • 7.12.9.5 The lrint and llrint functions (p: 233)
  • 7.22 Type-generic math <tgmath.h> (p: 335-337)
  • F.9.6.4 The rint functions (p: 463)
  • F.9.6.5 The lrint and llrint functions (p: 463)

See also