如何将 C# 中的 Knuth 哈希代码转换为 SQL 等效代码？

Question

任何人都可以帮我将下面的 C# 代码（Knuth hash）转换为 SQL 等效项吗？

/// <summary>
/// https://stackoverflow.com/a/9545731
/// </summary>
static string CalculateHash(string read)
{
    UInt64 hashedValue = 3074457345618258791ul;
    for (int i = 0; i < read.Length; i++)
    {
        hashedValue += read[i];
        hashedValue *= 3074457345618258799ul;
    }
    return hashedValue.ToString(CultureInfo.InvariantCulture);
}

我正在使用 Microsoft SQL Server 2016。

此外，正如here所指出的，在 SQL 中，您可以使用 NUMERIC(20) 数据类型来表示 64 位无符号整数值。

谢谢你。

Answer 1

我准备了两个潜在的 SQL 函数 - 一个使用

NUMERIC(38,0)

执行计算，另一个使用

BIGINT

执行计算。

BIGINT

版本需要在基础 Int64 值范围的限制内对乘法计算执行位片算术。尽管实现更加复杂，但它仍然可能优于

NUMERIC(38,0)

版本，因为处理器本身支持

BIGINT

加法、乘法以及各种按位运算。

NUMERIC(38,0)

是一种模拟数据类型，需要使用除法和余数运算。我没有进行性能测试。

这两个函数产生相同的结果，并且还与多个测试字符串的参考 C# 实现的结果相匹配，包括包含 16 位字符的字符串和 U+FFFF 以上 UNICODE 字符的代理对。

NUMERIC(38,0)

版本：

CREATE FUNCTION KnuthHashUnicode1(@String NVARCHAR(MAX))
RETURNS VARCHAR(20)
AS
BEGIN
    -- Adaptation of C# hash algorithm posted at https://stackoverflow.com/a/9545731
    -- WARNING: This hash is **not** crypographically secure.

    -- NOTE: This algorithm depends on the fact that the @Multiplier value is such
    -- that @Multiplier * @TwoPower64 does not exceed the NUMERIC(38,0) capacity.
  
    -- Key values
    DECLARE @Seed       NUMERIC(38,0) =  3074457345618258791
    DECLARE @Multiplier NUMERIC(38,0) =  3074457345618258799
    DECLARE @TwoPower64 NUMERIC(38,0) = 18446744073709551616 -- 2^64
    
    -- Initialize
    DECLARE @Hash NUMERIC(38,0) = @Seed
    
    -- Get the true length of string, including possible trailing spaces
    DECLARE @Len INT = DATALENGTH(@String) / 2
    
    DECLARE @Pos INT = 0
    WHILE @Pos < @Len
    BEGIN
        SET @Pos += 1
        DECLARE @Value BIGINT = UNICODE(SUBSTRING(@String, @Pos, 1))
        
        SET @Hash = (@Hash + @Value) % @TwoPower64
        SET @Hash = (@Hash * @Multiplier) % @TwoPower64
    END
    
    -- Format and return as string
    RETURN CAST(@Hash AS VARCHAR(20))
END

BIGINT

版本：

CREATE FUNCTION KnuthHashUnicode2(@String NVARCHAR(MAX))
RETURNS VARCHAR(20)
AS
BEGIN
    -- Adaptation of C# hash algorithm posted at https://stackoverflow.com/a/9545731
    -- WARNING: This hash is **not** crypographically secure.

    -- Key values are conveniently < 2^63, so they fit in a signed BIGINT.
    DECLARE @Seed BIGINT = 3074457345618258791
    DECLARE @Mult BIGINT = 3074457345618258799
    
    -- We will be doing arithmatic in three slices: 2 x 24-bit and 1 x 16-bit
    DECLARE @Mask24 BIGINT = 0xFFFFFF -- 24 bits (Lo and Md parts)
    DECLARE @Mask16 BIGINT = 0xFFFF   -- 16 bits (Hi part)
    
    DECLARE @SeedLo BIGINT = @Seed & @Mask24
    DECLARE @SeedMd BIGINT = (@Seed >> 24) & @Mask24
    DECLARE @SeedHi BIGINT = @Seed >> 48
    
    DECLARE @MultLo BIGINT = @Mult & @Mask24
    DECLARE @MultMd BIGINT = (@Mult >> 24) & @Mask24
    DECLARE @MultHi BIGINT = @Mult >> 48
    
    -- Initialize
    DECLARE @HashHi BIGINT = @SeedHi
    DECLARE @HashMd BIGINT = @SeedMd
    DECLARE @HashLo BIGINT = @SeedLo
    
    -- Get the true length of string, including possible trailing spaces
    DECLARE @Len INT = DATALENGTH(@String) / 2
    
    DECLARE @Pos INT = 0
    WHILE @Pos < @Len
    BEGIN
        SET @Pos += 1
        DECLARE @Value BIGINT = UNICODE(SUBSTRING(@String, @Pos, 1))
        
        -- Add with carry
        DECLARE @SumLo BIGINT = @HashLo + @Value
        DECLARE @SumMd BIGINT = @HashMd + (@SumLo >> 24)
        DECLARE @SumHi BIGINT = @HashHi + (@SumMd >> 24)
        SET @HashLo = @SumLo & @Mask24
        SET @HashMd = @SumMd & @Mask24
        SET @HashHi = @SumHi & @Mask16
        
        -- Cross-multiply with carry
        -- (No need to calculate product components > 64 bits)
        DECLARE @ProdLo BIGINT = (@HashLo * @MultLo)
        DECLARE @ProdMd BIGINT = (@HashMd * @MultLo)
                               + (@HashLo * @MultMd)
                               + (@ProdLo >> 24)
        DECLARE @ProdHi BIGINT = (@HashHi * @MultLo)
                               + (@HashMd * @MultMd)
                               + (@HashLo * @MultHi)
                               + (@ProdMd >> 24)
        SET @HashLo = @ProdLo & @Mask24
        SET @HashMd = @ProdMd & @Mask24
        SET @HashHi = @ProdHi & @Mask16
    END
    
    -- Combine slices
    DECLARE @Result BIGINT = (@HashHi << 48) | (@HashMd << 24) | (@HashLo)

    -- Convert to numeric and adjust for negative
    DECLARE @ResultNum NUMERIC(20,0) = CAST(@Result AS NUMERIC(20,0)) 
    IF @ResultNum < 0 SET @ResultNum += 18446744073709551616 -- 2^64

    -- Format and return as string
    RETURN CAST(@ResultNum AS VARCHAR(20))
END

结果示例：

字符串	结果1	结果2
（空字符串）	3074457345618258791	3074457345618258791
（单个空格）	16397105843297422473	16397105843297422473
世界你好	5485109609273439365	5485109609273439365
Hello World（带尾随空格）	10073154357816199819	10073154357816199819
αβγδ абвг你好世界∫∬∭∮🅐🅑🅒🅓	5168594500780613104	5168594500780613104
敏捷的棕色狐狸跳过了懒狗。	5118964073116902044	5118964073116902044

请参阅 this db<>fiddle 进行演示。