TSQL - Unique string generator, Sql Server

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/* input arguments */
declare @characterPool varchar(256) = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
declare @outputLength int = 32;

declare @n int = 0; /* counter */
declare @numLoops int = ceiling(log(len(@characterPool)) / log(2) * @outputLength / 128)
declare @e varbinary(128) = 0x; /* entropy */

while @n < @numLoops
begin
    set @e += cast(newid() as binary(16));
    set @n += 1;
end

declare @b int; /* byte */
declare @d int; /* dividend */
declare @out varchar(128) = '';

declare @outputBase int = len(@characterPool);
declare @entropyBytes int = len(@e);

declare @m int = 0;
while @m < @outputLength
begin
    set @b = 0;
    set @d = 0;
    set @n = 0;
    while @n < @entropyBytes
    begin
        set @b = (@b - @d * @outputBase) * 256 + cast(substring(@e, @n + 1, 1) as int);
        set @d = @b / @outputBase;
        set @e = cast(stuff(@e, @n + 1, 1, cast(@d as binary(1))) as varbinary(128));
        set @n += 1;
    end
    set @out += substring(@characterPool, @b - @d * @outputBase + 1, 1);
    set @m += 1;
end

select @out as "UniqueString"

View schema
Execution time: 0 sec, rows selected: 4142, rows affected: 0, absolute service time: 0,16 sec