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From: wmb@MITCH.ENG.SUN.COM
Newsgroups: comp.lang.forth
Subject: Metacompiling and C Forth 83
Message-ID: <9012121624.AA00871@ucbvax.Berkeley.EDU>
Date: 12 Dec 90 01:20:30 GMT
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Reply-To: wmb%MITCH.ENG.SUN.COM@SCFVM.GSFC.NASA.GOV
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> How slow would [C Forth 83] be, compared to a FORTH compiler written
> for any particular processor?

It depends on the machine architecture (i.e. how good it is at running
C and Forth), the quality of the C compiler, and the implementation
technique used for the native Forth under comparison.  Clearly, a
machine like an RTX-2000, which is optimized for Forth but which is
only a so-so C machine, will give you a different answer than a
SPARC, which is a good architecture for C but only so-so for Forth.

On SPARC, C Forth 83 runs about 50% slower than my direct-threaded
native SPARC Forth (i.e. the time ratio is 3:2), using the Sun optimizing
C compiler at high optimization levels.  This is probably close to
the best case.

On 68010, the time ratio is about 2:1, comparing the same things as for
SPARC (i.e. C Forth 83 compiled by Sun's optimizing C compiler compared
to my direct-threaded native 680x0 Forth).

On a PC, it is probably worse, but it depends strongly on the particular
C compiler.  The speed differences between C Forth 83 compiled under
several different PC C compilers are quite noticeable.  It also depends
strongly on whether it is compiled for 16 bit stacks or 32 bit stacks.

For the purpose that was being discussed (metacompiling eForth), I doubt
that speed differences of this order of magnitude matter very much.

Mitch Bradley, wmb@Eng.Sun.COM