Fortran vs. C for numerical work (SUMMARY)

[David Sielaff]

In article <6690:Nov3006:15:3890 at kramden.acf.nyu.edu> brnstnd at kramden.acf.nyu.edu (Dan Bernstein) writes:
>Several of you have been missing the crucial point.
>
>Say there's a 300 to 1 ratio of steps through a matrix to random jumps.
>On a Convex or Cray or similar vector computer, those 300 steps will run
>20 times faster. Suddenly it's just a 15-1 ratio, and a slow instruction
>outside the loop begins to compete in total runtime with a fast
>floating-point multiplication inside the loop.
>
>Anyone who doesn't think shaving a day or two off a two-week computation
>is worthwhile shouldn't be talking about efficiency.
>
>In article <7339 at lanl.gov> ttw at lanl.gov (Tony Warnock) writes:
>>       Model        Multiplication Time     Memory Latency
>>       YMP          5  clock periods         18 clock periods
>>       XMP          4  clock periods         14 clock periods
>>       CRAY-1       6  clock periods         11 clock periods
>
>Um, I don't believe those numbers. Floating-point multiplications and
>24-bit multiplications might run that fast, but 32-bit multiplications?
>Do all your matrices really fit in 16MB?

On late-model X-MP's and all Y-MP's, those times are correct for
32 bit integer multiplications.  The change (from 24 to 32 bit
multiplies) corresponds to when the address space on the
Cray 1/X-MP/Y-MP line was bumped up from 24 bits to 32 bits (it was
always 32 bits on a Cray-2).

But this certainly seems to be getting an awfully long way from C ;-)

Dave Sielaff
Cray Research, Inc.