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rint, lrint, llrint

From cppreference.com
< c‎ | numeric‎ | math
 
 
 
Common mathematical functions
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Nearest integer floating point operations
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rintlrintllrint
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Floating point manipulation functions
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Classification
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Macro constants
 
Defined in header <math.h>
float rintf( float arg );
(since C99)
double rint( double arg );
(since C99)
long double rintl( long double arg );
(since C99)
long lrintf( float arg );
(since C99)
long lrint( double arg );
(since C99)
long lrintl( long double arg );
(since C99)
long long llrintf( float arg );
(since C99)
long long llrint( double arg );
(since C99)
long long llrintl( long double arg );
(since C99)

Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode. If the result differs from arg (i.e., arg was not an integer value already), the floating-point exception FE_INEXACT is raised.

Contents

[edit] Parameters

arg - floating point value

[edit] Return value

The integer result of rounding arg

[edit] Notes

The only difference between nearbyint and rint is that rint may raise the FE_INEXACT floating-point exception, while nearbyint never raises it.

[edit] Example

#include <stdio.h>
#include <math.h>
#include <errno.h>
#include <fenv.h>
#include <limits.h>
#include <string.h>
 
#pragma STDC FENV_ACCESS ON
 
void show_fe_exceptions(void)
{
    printf("current exceptions raised: ");
    if(fetestexcept(FE_DIVBYZERO))     printf(" FE_DIVBYZERO");
    if(fetestexcept(FE_INEXACT))       printf(" FE_INEXACT");
    if(fetestexcept(FE_INVALID))       printf(" FE_INVALID");
    if(fetestexcept(FE_OVERFLOW))      printf(" FE_OVERFLOW");
    if(fetestexcept(FE_UNDERFLOW))     printf(" FE_UNDERFLOW");
    if(fetestexcept(FE_ALL_EXCEPT)==0) printf(" none");
    printf("\n");
}
 
void show_fe_rounding_method(void)
{
    printf("current rounding method:    ");
    switch (fegetround()) {
           case FE_TONEAREST:  printf ("FE_TONEAREST");  break;
           case FE_DOWNWARD:   printf ("FE_DOWNWARD");   break;
           case FE_UPWARD:     printf ("FE_UPWARD");     break;
           case FE_TOWARDZERO: printf ("FE_TOWARDZERO"); break;
           default:            printf ("unknown");
    };
    printf("\n");
}
 
int main(void)
{
    /* current rounding method:  to nearest                               */
    /* If the result is midway between two representable values, the even */
    /* representable is chosen.                                           */
    show_fe_rounding_method();
    printf("\n");
 
    printf("rint(+2.5)      = %+.1f\n", rint(+2.5));  /* even representable */
    printf("rint(-2.5)      = %+.1f\n", rint(-2.5));
    printf("rint(+1.5)      = %+.1f\n", rint(+1.5));  /* even representable */
    printf("rint(-1.5)      = %+.1f\n", rint(-1.5));
    printf("rint(+0.0)      = %+.1f\n", rint(+0.0));  /* all rounding modes */
    printf("rint(-0.0)      = %+.1f\n", rint(-0.0));  /*        "           */
    printf("rint(+INFINITY) = %+f\n",   rint(+INFINITY)); /*    "           */
    printf("rint(-INFINITY) = %+f\n",   rint(-INFINITY)); /*    "           */
    printf("rint(NAN)       = %f\n",    rint(NAN));   /*        "           */
    printf("\n");
 
    /* FE_INEXACT floating-point exception for finite non-integer arguments */
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("rint(2.5) = %.1f\n", rint(2.5));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
    printf("\n");
 
    printf("lrint(+2.5) = %+ld\n", lrint(+2.5));
    printf("lrint(-2.5) = %+ld\n", lrint(-2.5));
    printf("lrint(+1.5) = %+ld\n", lrint(+1.5));
    printf("lrint(-1.5) = %+ld\n", lrint(-1.5));
    printf("\n");
 
    /* rounded value is outside the range of the return type */
    /* neither domain nor range error occurs                 */
    printf("LONG_MAX            = %+ld\n", LONG_MAX);
    errno = 0; feclearexcept(FE_ALL_EXCEPT);
    printf("lrint(LONG_MAX+1.5) = %+ld\n", lrint(LONG_MAX+1.5));
    printf("%s\n",strerror(errno));
    show_fe_exceptions();
 
    return 0;
}

Possible output:

current rounding method:    FE_TONEAREST
 
rint(+2.5)      = +2.0
rint(-2.5)      = -2.0
rint(+1.5)      = +2.0
rint(-1.5)      = -2.0
rint(+0.0)      = +0.0
rint(-0.0)      = -0.0
rint(+INFINITY) = +inf
rint(-INFINITY) = -inf
rint(NAN)       = nan
 
rint(2.5) = 2.0
Success
current exceptions raised:  FE_INEXACT
 
lrint(+2.5) = +2
lrint(-2.5) = -2
lrint(+1.5) = +2
lrint(-1.5) = -2
 
LONG_MAX            = +9223372036854775807
lrint(LONG_MAX+1.5) = -9223372036854775808
Success
current exceptions raised:  FE_INVALID

[edit] See also

nearest integer using current rounding mode
(function) [edit]
(C99)
nearest integer not greater in magnitude than the given value
(function) [edit]