From: semler@
Newsgroups: comp.os.msdos.djgpp
Subject: Re: DJGPP Optimizing
Date: 31 Dec 1996 10:03:11 GMT
Organization: IBM Zurich Research Laboratory
Lines: 64
Message-ID: <5aaocv$mis@grimsel.zurich.ibm.com>
References: <19961231 DOT 163855 DOT 4983 DOT 3 DOT chambersb AT juno DOT com>
Reply-To: semler AT raleigh DOT ibm DOT com
NNTP-Posting-Host: semler.dk.ibm.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

In <19961231 DOT 163855 DOT 4983 DOT 3 DOT chambersb AT juno DOT com>, chambersb AT juno DOT com (Benjamin D Chambers) writes:

Ok thanks for the hints but I'm still having troubles:

1) The inner loop I talked about is

unsigned long i,run,u0,v0,du,dv,mask;
long *b1,b2;

for(i=run;i--) {
  u0 = (u0+du)&mask;
  v0 = (v0+dv)&mask;
 *b1++ = b2[((((unsigned long)v0)>>16)<<7)+((((unsigned long)u0)>>16))];
}

This compiles to:

L1220:
	fxch %st(2)
	fxch %st(4)
	fxch %st(5)
	fxch %st(3)
	fxch %st(6)
	fxch %st(2)
	fxch %st(2)
	fxch %st(6)
	fxch %st(3)
	fxch %st(5)
	fxch %st(4)
	fxch %st(2)
	movl -132(%ebp),%eax
	addl -232(%ebp),%eax
	movl -16(%ebp),%edx
	andl %edx,%eax
	movl %eax,-232(%ebp)
	movl -136(%ebp),%eax
	addl %ebx,%eax
	movl %eax,%ebx
	andl %edx,%ebx
	movl %ebx,%eax
	shrl $16,%eax
	sall $7,%eax
	movl -232(%ebp),%edx
	shrl $16,%edx
	addl %edx,%eax
	movl -120(%ebp),%esi
	movl (%esi,%eax,4),%eax
	movl -116(%ebp),%edi
	movl %eax,(%edi)
	addl $4,%edi
	movl %edi,-116(%ebp)
L1209:
	decl %ecx
	cmpl $-1,%ecx
	jne L1220

And the first 12 instructions are here in question... What do they do? Why are
they here?

2) I know that the intel processors has troubles with domains, but is there no
standard behaviour for the Gnu C about what to expect on this matter?

Kind regards and a Happy New Year!
Henning Semler