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From: dan@rna.UUCP (Dan Ts'o)
Newsgroups: net.arch
Subject: re: Using C as an aid to hand writing assembler
Message-ID: <491@rna.UUCP>
Date: Tue, 6-May-86 18:54:11 EDT
Article-I.D.: rna.491
Posted: Tue May  6 18:54:11 1986
Date-Received: Sat, 10-May-86 13:48:49 EDT
References: <817@harvard.UUCP> <Navajo.494> <460@cubsvax.UUCP> <850@harvard.UUCP> <839@umcp-cs.UUCP> <2107@peora.UUCP> <2110@gondor.UUCP> <36 May 86 22:54:11 GMT
Organization: Rockefeller Neurobiology
Lines: 32
Original-Subject: Re: Arch support for C

> 	Some years ago when I was learning 6800 assembler (anybody remember
> D2 kits?) I used to first write everything in C and then hand compile it
> into M6800 asm.  When I told my professor (are you reading this Professor
> Efe?) that I did this instead of drawing flow-charts, he laughed at me, but
> as long as you keep your code simple, the conversion is trivial and can be
> done in your head as fast as you can write down the asm code.  Perhaps the
> simplicity of the M6800 (dare I call it a RISC machine? :-)) makes this
> easier than for something like a vax, but I can still do it; let's see:
> 
> 	char i, j;
> 	j = 0;
> 	for (i = 0; i <= 10; i++)
> 	        j = j + i;
> 
> 	clr	j
> loop1:  clr	i
> 	cmp	i, #10
> 	bge	out
> 	lda	j
> 	adda	i
> 	sta	j
> 	lda	i
> 	inca
> 	sta	i
> 	bra     loop1:
> out:

	Not too good, I'm afraid. The loop1 label is misplaced - you "clr i"
on every iteration. Also #10 is octal 8 instead of 10. You probably don't want
the colon at the end of the "bra" statement. You don't want "bge out" but
"bgt out" (since you say i <= 10). And finally, i and j should be local
variables on the stack. I can see why your professor laughed.