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From: marc@noe.UUCP (Marc de Groot)
Newsgroups: comp.lang.forth
Subject: Re: Forth in C
Message-ID: <725@noe.UUCP>
Date: 22 Nov 89 01:41:57 GMT
References: <8911142050.AA16286@jade.berkeley.edu> <717@noe.UUCP> <7026@pt.cs.cmu.edu>
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Reply-To: marc@noe.UUCP (Marc de Groot)
Organization: Noe Systems, San Francisco
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In article <7026@pt.cs.cmu.edu> koopman@a.gp.cs.cmu.edu (Philip Koopman) writes:
>In article <717@noe.UUCP>, marc@noe.UUCP (Marc de Groot) writes:
>> I use the asm("..."); pseudo-op to assemble an indirect branch instruction.
>> This turns into some very efficient code, even with my awful pcc-derived
>> 80286 C compiler.
>How much faster did it go?  The PCC compilers I've seen tend to
>use an indirect jump table to implement case statements, which
>isn't that far away from what you're doing.  Did you measure
>enough speed improvement to be worthwhile?  Does your C compiler
>us jump tables?
Yes, my C compiler does use jump tables.  No, I did not actually time
it.  I looked at a disassembly of the code.  My token-threaded Forth
has the dictionary in an array of short.  That means that every
reference into the dictionary requires a left-shift of the subscript
and adding the dictionary's base address before fetching.  Then it
sets up the arguments for the jump through the table.  The indirect-
threaded code that I posted does not need to do this and uses
considerably fewer instructions.

^M


>
>-- Phil


-- 
Marc de Groot (KG6KF)                   These ARE my employer's opinions!
Noe Systems, San Francisco
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