[m-rev.] diff: improve efficiency of list__merge_sort

[Ralph Becket]

> From: Fergus Henderson [mailto:fjh at cs.mu.OZ.AU] 
> Sent: 28 August 2001 14:13
> 
> On 24-Aug-2001, Simon Taylor <stayl at cs.mu.OZ.AU> wrote:
> > 
> > library/list.m:
> > 	Improve efficiency of list__merge_sort by not recomputing
> > 	the length of the list at each step.
> 
> How much difference does this make?

If you're keen to speed up sorting long lists, you'd be best
off going via array__sort/1 which uses in-place SAMsort.

I suspect that the majority of calls to list__sort/1 are for
small lists where it's not worth the bother of changing to
an intermediate representation.

Perhaps after calculating the length of the input for the
first time in list__merge_sort you could make a decision as 
to which route to take.  That should work out quite nicely.

- Ralph
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