Question

How to use lrint() function to round a floating-point to an integer value using rounding direction fegetround in C++

Answer 1

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

using namespace std;

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

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

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

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

	return 0;

}

/*
run:

rounding to nearest :
lrint(3.3) = 3
lrint(3.5) = 4
lrint(4.5) = 4
lrint(4.6) = 5
lrint(-3.3) = -3
lrint(-3.5) = -4
lrint(-4.5) = -4
lrint(-4.6) = -5

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

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

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

*/

 

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