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From: barry@pico.math.ucla.edu (Barry Merriman)
Newsgroups: comp.sys.next
Subject: Re: NeXTStation Benchmark
Message-ID: <762@kaos.MATH.UCLA.EDU>
Date: 17 Nov 90 08:06:16 GMT
References: <743@kaos.MATH.UCLA.EDU> <1990Nov16.192938.17923@Neon.Stanford.EDU>
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Organization: UCLA Dept. of Math, UCLA Inst. for Fusion and Plasma Research
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In article <1990Nov16.192938.17923@Neon.Stanford.EDU> philip@pescadero.stanford.edu writes:

>Still, a factor of 2 difference looks suspicious. I decided to check this
>out myself. My results looked like this on the DECstation 3100:
>cc -O:
>0.6u 0.0s 0:00 82% 30+30k 3+0io 0pf+0w
>gcc -O:
>0.2u 0.0s 0:00 86% 30+31k 0+0io 0pf+0w
>Even worse - now gcc is 3 times faster. When I get bizarre results, I
>check them - so I looked at the output of the program. The result 
>is 1.00001 to the power 1000000, which my calculators claim is 22025.365.

22025.365 is the true result (according to a 16 digit calculation in mathematica)---the 
the other results are off due to accumulated errors in the single precision arithmetic, I guess. 

>Output from cc:
>  x = 22323.087891 (1% different from calculators)
>Output from gcc:
>  x = 0.000000 (seriously bogus)
>So - how about another round of runs, this time checking the output?

gcc gives the right output (22323.087891) on a SPARC. I don't
have gcc on our DEC, but it would appear it has a serious problem!

My program always gave the output x value, and while I didn't check it carefully,
I think it was the same on all machines I tried---definitely never 0!

>Not that I'd advocate wasting too much time on this - toy benchmarks don't
>tell you much anyway.

No, but on the other hand, at least we do know exactly what this 
benchmark does, and it is highly portable, even over the sneakernet :-)


--
Barry Merriman
UCLA Dept. of Math
UCLA Inst. for Fusion and Plasma Research
barry@math.ucla.edu (Internet)