Question

How to use llrint() function to round a floating-point to an integer value using rounding mode 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("llrint(3.3) = %lld\n", llrint(3.3));
    printf("llrint(3.5) = %lld\n", llrint(3.5));
    printf("llrint(4.5) = %lld\n", llrint(4.5));    
	printf("llrint(4.6) = %lld\n", llrint(4.6));
    printf("llrint(-3.3) = %lld\n", llrint(-3.3));
    printf("llrint(-3.5) = %lld\n", llrint(-3.5));
    printf("llrint(-4.5) = %lld\n", llrint(-4.5));    
	printf("llrint(-4.6) = %lld\n\n", llrint(-4.6));
	
	fesetround(FE_DOWNWARD);
    printf("rounding down: \n");
	printf("llrint(3.3) = %lld\n", llrint(3.3));
    printf("llrint(3.5) = %lld\n", llrint(3.5));
    printf("llrint(4.5) = %lld\n", llrint(4.5));    
	printf("llrint(4.6) = %lld\n", llrint(4.6));
    printf("llrint(-3.3) = %lld\n", llrint(-3.3));
    printf("llrint(-3.5) = %lld\n", llrint(-3.5));
    printf("llrint(-4.5) = %lld\n", llrint(-4.5));    
	printf("llrint(-4.6) = %lld\n\n", llrint(-4.6));
	
	fesetround(FE_UPWARD);
	printf("rounding up: \n");
	printf("llrint(3.3) = %lld\n", llrint(3.3));
    printf("llrint(3.5) = %lld\n", llrint(3.5));
    printf("llrint(4.5) = %lld\n", llrint(4.5));    
	printf("llrint(4.6) = %lld\n", llrint(4.6));
    printf("llrint(-3.3) = %lld\n", llrint(-3.3));
    printf("llrint(-3.5) = %lld\n", llrint(-3.5));
    printf("llrint(-4.5) = %lld\n", llrint(-4.5));    
	printf("llrint(-4.6) = %lld\n\n", llrint(-4.6));
	
	fesetround(FE_TOWARDZERO);
	printf("rounding toward zero: \n");
	printf("llrint(3.3) = %lld\n", llrint(3.3));
    printf("llrint(3.5) = %lld\n", llrint(3.5));
    printf("llrint(4.5) = %lld\n", llrint(4.5));    
	printf("llrint(4.6) = %lld\n", llrint(4.6));
    printf("llrint(-3.3) = %lld\n", llrint(-3.3));
    printf("llrint(-3.5) = %lld\n", llrint(-3.5));
    printf("llrint(-4.5) = %lld\n", llrint(-4.5));    
	printf("llrint(-4.6) = %lld\n\n", llrint(-4.6));
  
    return 0;
}
 
 
/*
run:
   
rounding to nearest :
llrint(3.3) = 3
llrint(3.5) = 4
llrint(4.5) = 4
llrint(4.6) = 5
llrint(-3.3) = -3
llrint(-3.5) = -4
llrint(-4.5) = -4
llrint(-4.6) = -5

rounding down:
llrint(3.3) = 3
llrint(3.5) = 3
llrint(4.5) = 4
llrint(4.6) = 4
llrint(-3.3) = -4
llrint(-3.5) = -4
llrint(-4.5) = -5
llrint(-4.6) = -5

rounding up:
llrint(3.3) = 4
llrint(3.5) = 4
llrint(4.5) = 5
llrint(4.6) = 5
llrint(-3.3) = -3
llrint(-3.5) = -3
llrint(-4.5) = -4
llrint(-4.6) = -4

rounding toward zero:
llrint(3.3) = 3
llrint(3.5) = 3
llrint(4.5) = 4
llrint(4.6) = 4
llrint(-3.3) = -3
llrint(-3.5) = -3
llrint(-4.5) = -4
llrint(-4.6) = -4

*/

 

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