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Subject: Re: Why is assembly more effecient than C?

Author: Robert Hyatt

Date: 06:17:09 09/28/98

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On September 28, 1998 at 03:01:19, Danniel Corbit wrote:

>On September 27, 1998 at 18:18:25, Robert Hyatt wrote:
>[snip]
>>not exactly.  IE I can't imagine that a C compiler + optimizer can beat
>>hand-tuned asm code, even if I write both the C and the asm code.  The
>>guys that write the optimizers are good, but they aren't as good as
>>someone that has been programming asm code for 30 years...
>>
>>The main reason everyone doesn't use ASM code is portability, *not*
>>speed.
>Risc C compilers can almost always outdo hand written code except for very small
>snippets.  For CISC I agree with you, especially Intel x86, since there are so
>many good Intel assembly programmers.  For thousands or millions of lines of C,
>an equivalent ASM is very hard to produce for Risc machines.


I'll take that bet.  :)

Remember:  RISC == Really Invented by Seymour Cray.  The cray has been
RISC from day one.  (Classic definition is one load/one store instruction,
everything operates on registers).  If someone writes an optimizer for a
processor, I *guarantee* you that I can write code better, because *every*
optimizer has concessions.  They are very good, no doubt, but *not* as good
as someone that understands the architecture in fine detail...  That's why
the scientific labs have folks that do nothing but take existing code and
hand-code assembly replacements to make them run faster.  This was Harry's
job at livermore lab from the time they got their first Cray-1...



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