String compare in words?

[qznc via Digitalmars-d-learn]

On Sunday, 29 May 2016 at 18:15:16 UTC, qznc wrote:
> On Sunday, 29 May 2016 at 17:38:17 UTC, Jonathan M Davis wrote:
>> And if you're not simply comparing for equality, what are you 
>> looking to figure out? Without more information about what 
>> you're trying to do, it's kind of hard to help you.
>
> If I write the comparison naively, the assembly clearly shows a 
> "movzbl" [0]. It loads a single byte! The other single byte 
> load is encoded in the address mode of "cmp". Implementation:
>
> bool stringcmp(string x, string y) {
>   foreach(i; 0..x.length) {
>     if (x[i] != y[i]) // byte compare
>       return false;
>   }
>   return true;
> }
>
> It makes no sense to load single bytes here. Since we only want 
> to check for equality, we could load two full words and compare 
> four or eight bytes in one go.

Ok, to answer my own question, this looks good:

bool string_cmp_opt(immutable(ubyte)[] x, immutable(ubyte)[] y) {
     pragma(inline, false);
     if (x.length != y.length) return false;
     int i=0;
     // word-wise compare is faster than byte-wise
     if (x.length > size_t.sizeof)
         for (; i < x.length - size_t.sizeof; i+=size_t.sizeof) {
             size_t* xw = cast(size_t*) &x[i];
             size_t* yw = cast(size_t*) &x[i];
             if (*xw != *yw) return false;
         }
     // last sub-word part
     for (; i < x.length; i+=1) {
         if (x[i] != y[i]) // byte compare
             return false;
     }
     return true;
}

Any comments or recommendations?