将图像哈希中使用的 C# BitCount 方法转换为涉及位运算符的 T-SQL

Question

我正在尝试将以下 BitCount 方法转换为 T-SQL，但我什至不知道如何开始。

例如，如何手动实例化一个 varbinary 变量，类似于下面的 bitCounts 数组。顺便说一句，原始代码位于 on github。将此方法转换为 T-SQL 的任何帮助都将非常有帮助。

几个输入，这个函数对应的输出是：

输入=34762711265992831；输出=23
输入=1130323790528512；输出=6
输入=33900573146222676；输出=17
输入=31648412230258808；输出=18
输入=31877043259982883；输出=11
输入=0；输出=0

private static byte[] bitCounts = {
    0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,4,5,5,6,5,6,6,7,5,6,6,7,6,7,7,8 
};

/// <summary>
/// Utility function for similarity.
/// </summary>
/// <param name="num">The hash we are counting.</param>
/// <returns>The total bit count.</returns>
private static uint BitCount(ulong num)
{
    uint count = 0;
    for (; num > 0; num >>= 8)
        count += bitCounts[(num & 0xff)];
    return count;
}

Answer 1

我在这里找到了答案http://www.dbforums.com/showthread.php?1630934-bit-counting

CREATE FUNCTION dbo.bit_count (@num AS BIGINT)RETURNS INT AS
BEGIN
    DECLARE @msb INT
    SET @msb = 0

    IF @num < 0
    BEGIN -- BIGINT is signed so treat the MSB differently
            SET @msb = 1
            SET @num = 0x7FFFFFFFFFFFFFFF & @num
    END

    SET @num = @num - ((@num / 2) & 0x5555555555555555)
    SET @num = (@num & 0x3333333333333333) + ((@num / 4) & 0x3333333333333333)
    SET @num = (@num + @num / 0x10) & 0x0F0F0F0F0F0F0F0F
    SET @num = @num + @num / 0x100
    SET @num = @num + @num / 0x10000
    SET @num = @num + @num / 0x100000000

    RETURN (@num & 0x3F) + @msb
END

将图像哈希中使用的 C# BitCount 方法转换为涉及位运算符的 T-SQL

Convert C# BitCount method used in image hashing to T-SQL involving Bitwise operators

tsql

bitwise-operators