Can this implementation of Damm algorithm be optimized?

[Nestor via Digitalmars-d-learn]

On Saturday, 11 February 2017 at 21:41:11 UTC, Era Scarecrow 
wrote:
> On Saturday, 11 February 2017 at 21:02:40 UTC, Era Scarecrow 
> wrote:
>>  Yes i know, which is why i had 3 to calculate 2 inputs 
>> because the third is the temp/previous calculation.
>
>  Alright I've found the bug and fixed it, and it passes with 
> flying colors (brute force tests up to 6 digits); However it 
> doesn't use the original function to build the table. So I'm 
> satisfied it will handle any length now.
>
>  But it seriously is a lot of overhead for such a simple 
> function.
>
> int[] buildMatrix2() {
>     string digits = "0123456789";
>     int[] l = new int[16*16*10];
>     l[] = -1; //printing the array it's obvious to see what is 
> padding
>     foreach(a; digits)
>     foreach(b; digits)
>     foreach(c; digits) {
>         int t = (a-'0')*10,
>             t2 = (QG10Matrix[(b - '0') + t]-'0') * 10,
>             off = (a - '0') << 8 | (b - '0') << 4 | (c - '0');
>         l[off] = (QG10Matrix[(c - '0') + t2]-'0')<<8;
>     }
>
>     return l;
> }
>
> char checkDigit2(string str) {
>     int tmpdigit = 0;
>     for(;str.length >= 2;str = str[2 .. $])
>         tmpdigit = 
> QG10Matrix2[tmpdigit|(str[0]-'0')<<4|(str[1]-'0')];
>
>     tmpdigit>>=8;
>     if (str.length==1)
>         return QG10Matrix[(str[0]-'0')+tmpdigit*10];
>
>     return (tmpdigit+'0') & 0xff;
> }

I fail to see where you are declaring QG10Matrix2, because 
apparently it's an array of chars, but buildMatrix2 returns an 
array of int (2560 elements??) with lots of -1 values.