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From: hamilton@uxc.cso.uiuc.edu
Newsgroups: comp.lang.c
Subject: Re: C vs assembler, or, Here We Go
Message-ID: <175400003@uxc.cso.uiuc.edu>
Date: Fri, 8-May-87 16:31:00 EDT
Article-I.D.: uxc.175400003
Posted: Fri May  8 16:31:00 1987
Date-Received: Sun, 10-May-87 05:01:00 EDT
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Nf-From: uxc.cso.uiuc.edu!hamilton    May  8 15:31:00 1987


jda@mas1 (James D. Allen) says:
> First penny)
> 	Some control flow techniques -- in particular coroutine
> linkage -- are inconvenient in C but achieved elegantly in assembly.
> To avoid a proliferation of global variables
> and/or "gotos" I have seen multitasking:
> ...
> used where an assembly language programmer would have invented
> coroutines even if he'd never heard of them.  Admittedly
> the multitasking design may be more readable; the point is
> that the assembly-level option is not readily available in C.

    Version 6 Unix C _had_ coroutines.  as it happens, i was hunting
for them just recently.  i found my old manual pages, but i can't find
an old enough tape around here to look for the sources.  coroutines
were implemented in a manner that paralleled fork's and pipe's, making
them very natural in a Unix context.

> Second Penny)
> 	#define	DSK_SEL	*(char *)0xf12345  /* WRITE but dont READ */
> 		DSK_SEL = 0;
> caused a parity error and had to be replaced with
> 		temp = 0; DSK_SEL = temp;
> The code generated was CLR.B and MOV.B respectively.  Can anyone
> elucidate?

    check your 68000 processor manual.  under "CLR", it points out:
"a memory destination will be read before it is written to".

	wayne hamilton
	U of Il and US Army Corps of Engineers CERL
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