MurMurHash64B in Transact-SQL

MurMurHash64B,sql

create function [dbo].[MurmurHash64B]
(
    @s varbinary(max),
    @seed bigint = 0
)
returns bigint
as
begin
    declare @len int = datalength(@s), @i int = 1
    declare @m bigint = 0x5bd1e995
    declare @h1 bigint = @len ^ (@seed & 0xffffffff)
    declare @h2 bigint = 0
    declare @k1 bigint, @k2 bigint

    while @len >= 8
    begin
        set @k1 = cast(convert(binary(4), reverse(substring(@s, @i, 4))) as int)
        set @k1 = (@k1 * @m) & 0xffffffff
        set @k1 ^= @k1 / 0x1000000
        set @k1 = (@k1 * @m) & 0xffffffff
        set @h1 = (@h1 * @m) & 0xffffffff
        set @h1 ^= @k1;

        set @k2 = cast(convert(binary(4), reverse(substring(@s, @i+4, 4))) as int)
        set @k2 = (@k2 * @m) & 0xffffffff
        set @k2 ^= @k2 / 0x1000000
        set @k2 = (@k2 * @m) & 0xffffffff
        set @h2 = (@h2 * @m) & 0xffffffff
        set @h2 ^= @k2
        set @len -= 8
        set @i += 8
    end

    if @len >= 4
    begin
        set @k1 = cast(convert(binary(4), reverse(substring(@s, @i, 4))) as int)
        set @k1 = (@k1 * @m) & 0xffffffff
        set @k1 ^= @k1 / 0x1000000
        set @k1 = (@k1 * @m) & 0xffffffff
        set @h1 = (@h1 * @m) & 0xffffffff
        set @h1 ^= @k1
        set @len -= 4
        set @i += 4
    end

    if @len >= 1
    begin
        if @len >= 2 
        begin
            if @len >= 3
                set @h2 ^= ascii(substring(@s, @i+2, 1)) * 0x10000
            set @h2 ^= ascii(substring(@s, @i+1, 1)) * 0x100
        end
        set @h2 ^= ascii(substring(@s, @i, 1))
        set @h2 = (@h2 * @m) & 0xffffffff
    end

    set @h1 = ((@h1 ^ (@h2 / 0x40000)) * @m) & 0xffffffff
    set @h2 = ((@h2 ^ (@h1 / 0x400000)) * @m) & 0xffffffff
    set @h1 = ((@h1 ^ (@h2 / 0x20000)) * @m) & 0xffffffff
    set @h2 = ((@h2 ^ (@h1 / 0x80000)) * @m) & 0xffffffff

    declare @h bigint
    if (@h1 & 0x80000000) <> 0
    begin
        set @h1 &= 0x7fffffff
        set @h = (@h1 * 0x100000000) | 0x8000000000000000
    end
    else
        set @h = @h1 * 0x100000000

    set @h |= @h2

    return @h
end

MSSQL is capable of storing 64-bit variables, but it doesn't support unsigned integer types, and treats arithmetic overflow as an exception. So the B flavor, which was originally geared towards 32-bit machines, is a better fit than A.

The official home of MurmurHash is at Github.

Update: there's also a MySQL implementation here.