From:	Daniel <entropic AT mpx DOT com DOT au>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Question about long long math on intel archs
Date:	Fri, 05 Feb 1999 13:09:33 +1100
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Hullo,

  
  I went back today and did a comparison of long multiplication's
versus long-long's.  (once again with the poor, decaying old 486)
This time i did it in ms-dos mode and found that it was moderately
faster than under the win95 dos-box.

Did 1000000 long multiply's in 0.879121 seconds.
Did 5000000 long multiply's in 4.3956 seconds.
Did 10000000 long multiply's in 8.73626 seconds.
Did 50000000 long multiply's in 43.7363 seconds.

Did 1000000 long long multiplies in 1.7033 seconds.
Did 5000000 long long multiplies in 8.35165 seconds.
Did 10000000 long long multiplies in 16.8132 seconds.
Did 50000000 long long multiplies in 83.9011 seconds.

More important than the actual numbers is the ratio's:

1000000 long-long's/long's    = 1.9375
5000000 long-long's/long's    = 1.9
10000000 long-long's / long's = 1.925
50000000 long-long's / long's = 1.918

I would have expected the 64-bit operations to take twice as long, but 
in fact they were a bit quicker than that.  There seems to be no
increased
overhead when multiplying long long int's.

daniel.


PS:  i hope nobody was compiling this code with optimisation on.
     when i do that everything is much MUCH faster and long and
long-long
     ops take exactly the same amount of time.  I assume this is becuz
     gcc see's the multiplications as useless, since we never use the
values
     of foo and bar.

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