Question

I have a double which has actual value (as seen from the debugger) val = 1.5530000000000002

however if I print it like string.Format("{0}", val) I get “1.553” which is realistic value I am looking for.

the 1.5530000000000002 comes from some socket API and I cant change that. But I need 1.553..

what shall I do?

Please note I receive thousands of these per sec. I can’t afford tinkering with the Math class or converting them forth and back. any consolations?

Answer 1

I decided to upscale them to ints. I can do it because I know how many significant digits are in the number.

int real = (int)(dbl * multiplier);

I am sure decimals will be slower simply because I dont have x128 CPU and memory bus. Using Math is out questions ever.

sorry for the blur with casting to float earlier.

EDIT OK. So I got that SO now is not free anymore. Each question need now attention which is costly in time… Here is the code which answers why I will not use Decimals and Math.

class Program
{
    static void Main(string[] args)
    {
        Start();
        Console.ReadLine();                
    }

    static int TESTS = 10;
    static int LOOPS = 50000;

    static double d1 = 1.5530000000000002;
    static double d2 = 1.5531;

    static double dResult;
    static int iResult;
    static decimal cResult;

    static void Start()
    {
        // actual test
        for (int x = 0; x < TESTS; x++)
        {
            Stopwatch sw = new Stopwatch();

            long tick1, tick2, tick3;
            sw.Start();
            for (int j = 0; j < LOOPS; j++)
            {
                dResult = Math.Round(d1 / 2.0, 4);
                dResult = Math.Round(d2 / 2.0, 4);
            }
            sw.Stop();

            tick1 = sw.ElapsedTicks;

            sw.Restart();
            for (int j = 0; j < LOOPS; j++)
            {
                iResult = (int)(d1 / 2.0 * 10000.0);
                iResult = (int)(d2 / 2.0 * 10000.0);
            }
            sw.Stop();

            tick2 = sw.ElapsedTicks;

            sw.Restart();
            for (int j = 0; j < LOOPS; j++)
            {
                cResult = decimal.Round((decimal)d1, 4);
                cResult = decimal.Round((decimal)d2, 4);
            }
            sw.Stop();

            tick3 = sw.ElapsedTicks;

            Console.WriteLine("Math {0} Int {1} Decimal {2}", tick1, tick2, tick3);
        }
    }
}

first part – is Math, second is what I am intended to use (conversion to int), and the third is Decimals.

The results on my i7 as follows – 12K ticks, 700 ticks, 35K ticks respectively.