I wrote:
[...]

> I used the more complicated, shift-based approach because it
> guarantees that greater-than/less-than comparisons on the prefix
> will yield the same results as strcasecmp on the first 4 bytes.
> This makes it possible to use the prefix in the comparator
> function in the big qsort in apr_table_overlap, which does
> a *lot* of strcasecmp calls otherwise. 


hmmm...I'm having second thoughts about optimizing the prefix
design for apr_table_overlap.  Rather than trying to eliminate
strcasecmp calls within the qsort, it may be better to eliminate
the qsort altogether.

I have an idea for how to do this...if it works, we can use
Cliff's faster prefix code for get/set operations and still
speed up apr_table_overlap.

If all goes well, I'll post an updated patch later this weekend.

--Brian