Question

How to use llrint() function to round a floating-point to an integer value using rounding mode in C++

Answer 1

#include <iostream>
#include <cmath>
#include <cfenv>  

using namespace std;

int main()
{
	fesetround(FE_TONEAREST);
	cout << "rounding to nearest :" << endl;
	cout << "llrint(3.3) = " << llrint(3.3) << endl;
	cout << "llrint(3.5) = " << llrint(3.5) << endl;
	cout << "llrint(4.5) = " << llrint(4.5) << endl;
	cout << "llrint(4.6) = " << llrint(4.6) << endl;
	cout << "llrint(-3.3) = " << llrint(-3.3) << endl;
	cout << "llrint(-3.5) = " << llrint(-3.5) << endl;
	cout << "llrint(-4.5) = " << llrint(-4.5) << endl;
	cout << "llrint(-4.6) = " << llrint(-4.6) << endl << endl;

	fesetround(FE_DOWNWARD);
	cout << "rounding down: " << endl;
	cout << "llrint(3.3) = " << llrint(3.3) << endl;
	cout << "llrint(3.5) = " << llrint(3.5) << endl;
	cout << "llrint(4.5) = " << llrint(4.5) << endl;
	cout << "llrint(4.6) = " << llrint(4.6) << endl;
	cout << "llrint(-3.3) = " << llrint(-3.3) << endl;
	cout << "llrint(-3.5) = " << llrint(-3.5) << endl;
	cout << "llrint(-4.5) = " << llrint(-4.5) << endl;
	cout << "llrint(-4.6) = " << llrint(-4.6) << endl << endl;;

	fesetround(FE_UPWARD);
	cout << "rounding up: " << endl;
	cout << "llrint(3.3) = " << llrint(3.3) << endl;
	cout << "llrint(3.5) = " << llrint(3.5) << endl;
	cout << "llrint(4.5) = " << llrint(4.5) << endl;
	cout << "llrint(4.6) = " << llrint(4.6) << endl;
	cout << "llrint(-3.3) = " << llrint(-3.3) << endl;
	cout << "llrint(-3.5) = " << llrint(-3.5) << endl;
	cout << "llrint(-4.5) = " << llrint(-4.5) << endl;
	cout << "llrint(-4.6) = " << llrint(-4.6) << endl << endl;

	fesetround(FE_TOWARDZERO);
	cout << "rounding toward zero: " << endl;
	cout << "llrint(3.3) = " << llrint(3.3) << endl;
	cout << "llrint(3.5) = " << llrint(3.5) << endl;
	cout << "llrint(4.5) = " << llrint(4.5) << endl;
	cout << "llrint(4.6) = " << llrint(4.6) << endl;
	cout << "llrint(-3.3) = " << llrint(-3.3) << endl;
	cout << "llrint(-3.5) = " << llrint(-3.5) << endl;
	cout << "llrint(-4.5) = " << llrint(-4.5) << endl;
	cout << "llrint(-4.6) = " << llrint(-4.6) << endl;

	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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