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What is the most efficient way to truncate a number with a certain accuracy?

What is the most efficient way to truncate a number with a certain accuracy?

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3 answers

In DateTime, Milliseconds are always between 0 and 999, so you have nothing to do.

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int ms = Convert.ToInt32(
             Convert.ToString(DateTime.Now.Millisecond).Substring(0, 3));

or

double Length = Math.Pow(10, (DateTime.Now.Millisecond.ToString().Length - 3));

double Truncate = Math.Truncate((double)DateTime.Now.Millisecond / Length);

EDIT:

After running both of the code below, which I will post, the dual method works well due to the reuse of variables. During an iteration of 5,000,000 DateTime.Now (in which many of both checks will be skipped), the method SubString()took 9598 ms, and the method Doubletook 6754 ms.

EDIT # 2: Edited in * 1000 in tests to make sure iterations are running.

The code used to verify is as follows:

        Stopwatch stop = new Stopwatch();
        stop.Start();

        for (int i = 0; i < 5000000; i++)
        {
            int MSNow = DateTime.Now.Millisecond * 1000;

            if (MSNow.ToString().Length > 2)
            {
                int ms = Convert.ToInt32(
                    Convert.ToString(MSNow).Substring(0, 3));
            }
        }

        stop.Stop();

        Console.WriteLine(stop.ElapsedMilliseconds);

        stop = new Stopwatch();
        stop.Start();

        for (int i = 0; i < 5000000; i++)
        {
            int MSNow = DateTime.Now.Millisecond * 1000;
            int lengthMS = MSNow.ToString().Length;

            if (lengthMS > 2)
            {
                double Length = Math.Pow(10, (lengthMS - 3));
                double Truncate = Math.Truncate((double)MSNow / Length);
            }
        }

        stop.Stop();

        Console.Write(stop.ElapsedMilliseconds);

        Console.ReadKey();
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Math.Floor(num * Math.Pow(10, x) + 0.5) / Math.Pow(10, x)

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