[Gcl-devel] Re: twc

[Camm Maguire]

Greetings!

Robert Boyer <address@hidden> writes:

> > Just a note that another incarnation of twc in now installed under /p/bin.
> 
> Thanks.  I'll get right on running the Nqthm-1992 tests.  I have hit one
> obscure problem, but I think it may be reproducible though it takes a long
> time to produce, so I may be able to send you a half-way decent bug report.
> 
> > This is a question of data locality
> 
> That's the best guess I have, too, but my guess is not worth a nickel in this
> territory.  Staying in the cache makes soooo much difference these days, it
> seems.  The funny thing is that since GCL "knows" the current top and bottom
> of the small fixnum range, it can "tell" merely from an address that a thing
> is a small fixnum, and if so, even what its value is from the address without
> having to actually go to the memory where the type and value are stored.  But
> such extra tests might slow other things down, e.g., for large fixnums.
> 

This idea is so beautiful I can't believe it hasn't arisen before!
Thanks so much for the suggestion!  What this appears to offer at a
minimum is immediate fixnums with no extra space allocation in the
range of +- 512*1024*1024 at least on x86 (the beginning of the .text
section is at 0x8000000 here, and my understanding is that no
addresses beneath this can appear in the heap.)

Take care,

> > a fixnum_times function in num_arith.c 
> > ... cuts the time for this benchmark in half
> 
> Another Camm miracle!!
> 
> > don't know how important such types of calculation are
> 
> I strongly believe that matrix multiplication is among the most important and
> common numeric calculations, so this is a terrific win I suspect.  However,
> people who want to do numeric calculations typically use FORTRAN and floating
> point.
> 
> > There are prefetch instructions on most modern machines
> 
> I've never even heard of that sort of thing, so cannot make any useful
> comment.
> 
> Thanks!
> 
> Bob
> 
> 
> 
> 

-- 
Camm Maguire                                            address@hidden
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"The earth is but one country, and mankind its citizens."  --  Baha'u'llah