Faster alternative to Convert.ToDouble(string)

Question

Is there a faster way to convert a string to double than Convert.ToDouble?

I have monitored System.Conv

Answer 1

You can save about 10% by calling Double.TryParse with specific cached instances of NumberStyles and IFormatProvider (i.e. CultureInfo):

var style = System.Globalization.NumberStyles.AllowDecimalPoint;
var culture = System.Globalization.CultureInfo.InvariantCulture;
double.TryParse("1.34515", style, culture, out x);

Both Convert.ToDouble and Double.Parse or Double.TryParse have to assume the input can be in any format. If you know for certain that your input has a specific format, you can write a custom parser that performs much better.

Here's one that converts to decimal. Conversion to double is similar.

static decimal CustomParseDecimal(string input) {
    long n = 0;
    int decimalPosition = input.Length;
    for (int k = 0; k < input.Length; k++) {
        char c = input[k];
        if (c == '.')
            decimalPosition = k + 1;
        else
            n = (n * 10) + (int)(c - '0');
    }
    return new decimal((int)n, (int)(n >> 32), 0, false, (byte)(input.Length - decimalPosition));
}

My benchmarks show this to be about 5 times faster than the original for decimal, and up to 12 times if you use ints.