c# - 最快的 StringBuilder 追加整数

Question

以最少的分配量将整数附加到 StringBuilder。有没有更快的方法？

    public static void AppendInvariant(this StringBuilder builder, int value)
    {
        // Deal with negative numbers
        if (value < 0)
        {
            builder.Append('-');
            uint uint_value = uint.MaxValue - ((uint)value) + 1; //< This is to deal with Int32.MinValue
            AppendInvariant(builder, uint_value);
        }
        else
        {
            AppendInvariant(builder, (uint)value);
        }
    }

    public static void AppendInvariant(this StringBuilder builder, uint value)
    {
        if (value == 0)
        {
            builder.Append('0');
            return;
        }

        // Pad out space for writing.
        int length = UintLength(value);
        builder.Append('0', length);
        length = builder.Length;

        uint tmp_value;
        do
        {
            tmp_value = value;
            value /= 10;
            builder[--length] = (char)('0' + (tmp_value - value * 10));
        } while (value > 0);
    }

    private static int UintLength(uint i)
    {
        if (i < 100000)
        {
            if (i < 10) return 1;
            if (i < 100) return 2;
            if (i < 1000) return 3;
            if (i < 10000) return 4;
            return 5;
        }
        else
        {
            if (i < 1000000) return 6;
            if (i < 10000000) return 7;
            if (i < 100000000) return 8;
            if (i < 1000000000) return 9;
            return 10;
        }
    }

Answer 1

以下实现大约快 2 倍。

它通过使用一个包含 100 个元素的预分配字符串表来最小化 StringBuilder 调用来做到这一点

private static readonly string[] UIntPairStrings =
    Enumerable.Range(0, 100).Select(n => n.ToString("00")).ToArray();

并且还通过从高到低处理 2 位数字对中的输入值来最小化除法数(以补偿存储空间不足)。这样操作执行不超过 5 个 Append 调用。

private static readonly uint[] UIntPairScales = { 100000000, 1000000, 10000, 100 };

public static void AppendInvariant(this StringBuilder builder, uint value)
{
    bool next = false;
    foreach (var scale in UIntPairScales)
    {
        if (value >= scale)
        {
            uint pair = value / scale;
            if (!next && pair < 10)
                builder.Append((char)('0' + pair));
            else
                builder.Append(UIntPairStrings[pair]);
            value -= pair * scale;
            next = true;
        }
        else if (next)
        {
            builder.Append("00");
        }
    }
    if (!next && value < 10)
        builder.Append((char)('0' + value));
    else
        builder.Append(UIntPairStrings[value]);
}