NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/7783

Internet Message Format | 1996-08-05 | 1.9 KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: [Perf:] mem*() procs vs. array looping
Date: Wed, 28 Feb 96 20:03:43 GMT
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References: <4glkq1$[e-mail]> <4h1n14$[e-mail]>
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In article <4h1n14$[e-mail]>
           [e-mail]
           "Scott McMahan - Softbase Systems" writes:

>4. I had a program where memset was THE bottleneck, taking up more time
>than I/O. I re-wrote a memory zeroing function using the most unrolled,
>efficient loop I could write, and it was still orders of magnitude
>slower than the system memset.  No way I could make it faster in C.
>
>5. WRT #4, I removed the memset. It was initializing a buffer, and I
>said "forget it" and used the uninitialized buffer and took my chances.

What you are suggesting is that you deliberately broke the code. What you
should have done is analyse the need for zeroing the buffer. That the
code still worked after the change implies that the zeroing was either
not necessary or you were depending on the memory allocated to you
being zeroed to start with. memset is unlikely to be a bottleneck unless
it is used repeatedly and extensively. In that case it is unlikely that
you would get such a guarantee and you were using it inappropriately
in the first place.

>Changing the design was more effecient than coding hokey
>optimizations!

That is usually true but what you describe above is a 'hokey optimization',
not a change of design.

--
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Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
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