Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: Notesfiles $Revision: 1.7.0.10 $; site mirror
Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!ima!inmet!mirror!rs
From: rs@mirror.UUCP
Newsgroups: net.lang.c
Subject: Re: Orphaned Response
Message-ID: <6000010@mirror>
Date: Thu, 27-Mar-86 09:21:00 EST
Article-I.D.: mirror.6000010
Posted: Thu Mar 27 09:21:00 1986
Date-Received: Sat, 12-Apr-86 21:59:04 EST
References: <1700003@umn-cs>
Lines: 49
Nf-ID: #R:umn-cs:-170000300:mirror:6000010:000:1357
Nf-From: mirror.UUCP!rs    Mar 27 09:21:00 1986



A friend of mine recently did what you want.  We were running UniPlus
SysV on a 68000.  He was doing image compression and needed to sample
every n'th bit in a source, writing it out as the m'th bit in the
destination.  The 68000 "test bit specified by register X" was too
slow, and he also wanted to unroll the loops.  As I remember, the code
went something like this:

typedef int	(*PFI)();
typedef short	  WORD;
extern char	*malloc();

PFI
generate(count)
    int		 count;
{
    WORD	*base;
    WORD	*p;

    base = p = malloc(sub_size);
    *p++ = prolog;				/* he had the actual	*/
    *p++ = prolog;				/* hex words of the	*/
    while (--count >= 0) {
	*p++ = test_bit;			/* code here, not these	*/
	*p++ = branch_if_zero .+2;		/* "mnemonics"		*/
	*p++ = mv 0,(a0);
	*p++ = skip;
	*p++ = mv 1,(a0);
	*p++ = decrement and branch if non-zero .-5;
    }
    *p++ = epilog;
    *p++ = return;
    return((PFI)base);
}

Then, in the main routine he had something like this:
    PFI *p, generate();
    p =generate(5);
    (*p)();

I may have a cast or two slightly wrong, but the basic principle
is sound.  (Well, it worked, at any rate; I don't know how sound
the basic principle really is :-)

--
Rich $alz	{mit-eddie, ihnp4!inmet, wjh12, cca, datacube}!mirror!rs
Mirror Systems	2067 Massachusetts Avenue  Cambridge, MA, 02140
Telephone:	6,176,610,777