更快的decimal.Parse替代品

Question

我注意到decimal.Parse(number, NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture)比基于Jeffrey Sax的代码的自定义十进制解析方法慢大约100%,该代码来自Faster替代Convert.ToDouble

public static decimal ParseDecimal(string input) {
    bool negative = false;
    long n = 0;

    int len = input.Length;
    int decimalPosition = len;

    if (len != 0) {
        int start = 0;
        if (input[0] == '-') {
            negative = true;
            start = 1;
        }

        for (int k = start; k < len; 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, negative, (byte)(len -decimalPosition));
}

我认为这是因为本机decimal.Parse旨在与数字风格和文化信息斗争.

但是,上面提到的方法不使用第三个参数hi字节,new decimal因此它不适用于较大的数字.

是否有更快的替代方法decimal.Parse将只包含数字和小数点的字符串转换为十进制,这将适用于大数字？

编辑:基准:

var style = System.Globalization.NumberStyles.AllowDecimalPoint;
var culture = System.Globalization.CultureInfo.InvariantCulture;
System.Diagnostics.Stopwatch s = new System.Diagnostics.Stopwatch();
s.Reset();
s.Start();
for (int i=0; i<10000000; i++)
{
    decimal.Parse("20000.0011223344556", style, culture);
}
s.Stop();
Console.WriteLine(s.Elapsed.ToString());

s.Reset();
s.Start();
for (int i=0; i<10000000; i++)
{
    ParseDecimal("20000.0011223344556");
}
s.Stop();
Console.WriteLine(s.Elapsed.ToString());

输出:

00:00:04.2313728
00:00:01.4464048

在这种情况下,自定义ParseDecimal明显快于decimal.Parse.

Answer 1

感谢您的所有评论,这让我有了更多的见解.最后我做了如下.如果输入太长,则它将输入字符串分开,并使用long解析第一部分,其余部分使用int,它仍然比decimal.Parse快.

这是我的最终生产代码:

public static int[] powof10 = new int[10]
{
    1,
    10,
    100,
    1000,
    10000,
    100000,
    1000000,
    10000000,
    100000000,
    1000000000
};
public static decimal ParseDecimal(string input)
{
    int len = input.Length;
    if (len != 0)
    {
        bool negative = false;
        long n = 0;
        int start = 0;
        if (input[0] == '-')
        {
            negative = true;
            start = 1;
        }
        if (len <= 19)
        {
            int decpos = len;
            for (int k = start; k < len; k++)
            {
                char c = input[k];
                if (c == '.')
                {
                    decpos = k +1;
                }else{
                    n = (n *10) +(int)(c -'0');
                }
            }
            return new decimal((int)n, (int)(n >> 32), 0, negative, (byte)(len -decpos));
        }else{
            if (len > 28)
            {
                len = 28;
            }
            int decpos = len;
            for (int k = start; k < 19; k++)
            {
                char c = input[k];
                if (c == '.')
                {
                    decpos = k +1;
                }else{
                    n = (n *10) +(int)(c -'0');
                }
            }
            int n2 = 0;
            bool secondhalfdec = false; 
            for (int k = 19; k < len; k++)
            {
                char c = input[k];
                if (c == '.')
                {
                    decpos = k +1;
                    secondhalfdec = true;
                }else{
                    n2 = (n2 *10) +(int)(c -'0');
                }
            }
            byte decimalPosition = (byte)(len -decpos);
            return new decimal((int)n, (int)(n >> 32), 0, negative, decimalPosition) *powof10[len -(!secondhalfdec ? 19 : 20)] +new decimal(n2, 0, 0, negative, decimalPosition);
        }
    }
    return 0;
}

基准代码:

const string input = "[inputs are below]";
var style = System.Globalization.NumberStyles.AllowDecimalPoint | System.Globalization.NumberStyles.AllowLeadingSign;
var culture = System.Globalization.CultureInfo.InvariantCulture;
System.Diagnostics.Stopwatch s = new System.Diagnostics.Stopwatch();
s.Reset();
s.Start();
for (int i=0; i<10000000; i++)
{
    decimal.Parse(input, style, culture);
}
s.Stop();
Console.WriteLine(s.Elapsed.ToString());

s.Reset();
s.Start();
for (int i=0; i<10000000; i++)
{
    ParseDecimal(input);
}
s.Stop();
Console.WriteLine(s.Elapsed.ToString());

在我的i7 920上的结果:

输入:123.456789

00:00:02.7292447
00:00:00.6043730

输入:999999999999999123.456789

00:00:05.3094786
00:00:01.9702198

输入:1.0

00:00:01.4212123
00:00:00.2378833

输入:0

00:00:01.1083770
00:00:00.1899732

输入:-3.3333333333333333333333333333333

00:00:06.2043707
00:00:02.0373628

如果输入仅包含0-9 ,. 并且可选地 - 在开始时,这个自定义函数明显更快地将字符串解析为十进制.