Question

How to use rint() function to round N to an integral value using the rounding direction fegetround in C

Answer 1

#include <stdio.h>     
#include <math.h>
#include <fenv.h> 
 
int main(int argc, char **argv)
{   
	fesetround(FE_TONEAREST); 
    printf("rounding to nearest :\n");
    printf("rint(3.3) = %.1f\n", rint(3.3));
    printf("rint(3.5) = %.1f\n", rint(3.5));
    printf("rint(4.5) = %.1f\n", rint(4.5));    
    printf("rint(4.6) = %.1f\n", rint(4.6));
    printf("rint(-3.3) = %.1f\n", rint(-3.3));
    printf("rint(-3.5) = %.1f\n", rint(-3.5));
    printf("rint(-4.5) = %.1f\n", rint(-4.5));    
    printf("rint(-4.6) = %.1f\n\n", rint(-4.6));
     
    fesetround(FE_DOWNWARD);
    printf("rounding down: \n");
    printf("rint(3.3) = %.1f\n", rint(3.3));
    printf("rint(3.5) = %.1f\n", rint(3.5));
    printf("rint(4.5) = %.1f\n", rint(4.5));    
    printf("rint(4.6) = %.1f\n", rint(4.6));
    printf("rint(-3.3) = %.1f\n", rint(-3.3));
    printf("rint(-3.5) = %.1f\n", rint(-3.5));
    printf("rint(-4.5) = %.1f\n", rint(-4.5));    
    printf("rint(-4.6) = %.1f\n\n", rint(-4.6));
     
    fesetround(FE_UPWARD);
    printf("rounding up: \n");
    printf("rint(3.3) = %.1f\n", rint(3.3));
    printf("rint(3.5) = %.1f\n", rint(3.5));
    printf("rint(4.5) = %.1f\n", rint(4.5));    
    printf("rint(4.6) = %.1f\n", rint(4.6));
    printf("rint(-3.3) = %.1f\n", rint(-3.3));
    printf("rint(-3.5) = %.1f\n", rint(-3.5));
    printf("rint(-4.5) = %.1f\n", rint(-4.5));    
    printf("rint(-4.6) = %.1f\n\n", rint(-4.6));
     
    fesetround(FE_TOWARDZERO);
    printf("rounding toward zero: \n");
    printf("rint(3.3) = %.1f\n", rint(3.3));
    printf("rint(3.5) = %.1f\n", rint(3.5));
    printf("rint(4.5) = %.1f\n", rint(4.5));    
    printf("rint(4.6) = %.1f\n", rint(4.6));
    printf("rint(-3.3) = %.1f\n", rint(-3.3));
    printf("rint(-3.5) = %.1f\n", rint(-3.5));
    printf("rint(-4.5) = %.1f\n", rint(-4.5));    
    printf("rint(-4.6) = %.1f\n\n", rint(-4.6));
  
    return 0;
}
 
/*
run:
   
rounding to nearest :
rint(3.3) = 3.0
rint(3.5) = 4.0
rint(4.5) = 4.0
rint(4.6) = 5.0
rint(-3.3) = -3.0
rint(-3.5) = -4.0
rint(-4.5) = -4.0
rint(-4.6) = -5.0

rounding down:
rint(3.3) = 3.0
rint(3.5) = 3.0
rint(4.5) = 4.0
rint(4.6) = 4.0
rint(-3.3) = -4.0
rint(-3.5) = -4.0
rint(-4.5) = -5.0
rint(-4.6) = -5.0

rounding up:
rint(3.3) = 4.0
rint(3.5) = 4.0
rint(4.5) = 5.0
rint(4.6) = 5.0
rint(-3.3) = -3.0
rint(-3.5) = -3.0
rint(-4.5) = -4.0
rint(-4.6) = -4.0

rounding toward zero:
rint(3.3) = 3.0
rint(3.5) = 3.0
rint(4.5) = 4.0
rint(4.6) = 4.0
rint(-3.3) = -3.0
rint(-3.5) = -3.0
rint(-4.5) = -4.0
rint(-4.6) = -4.0

*/

 

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