better ratfor ?

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2 total messages Started by btb Tue, 18 Nov 1986 18:48

#4462

Author: btb
Date: Tue, 18 Nov 1986 18:48

39 lines
1806 bytes

Hello,
	Does anybody know of a good ratfor preprocessor... one that doesn't
have some of the problems that our 3 have.... one that knows about f77?
	As an example, the ratfor for loop:

		for (i=1; i<=n; i = i + 1)

translates into the horrible:

		i = 1
		if (.not. (i .le. n)) goto (end of loop)
		...
		i = i + 1 (goto if)

rather than into the much more efficient:

		i = 1
		if (i .gt. n) goto (end of loop)
		...
		i = i + 1 (etc.)

this may not seem like much, but I have benchmarked the above optimization
change against the original code from a ratfor version of sieve, and it 
makes a factor of 2 difference... who knows how much more could be improved?
(Incidentally, the ratfor fortran sieve ran 5 times slower than either the
f77, or C sieve)
	We have a huge programming system all written in rat4... (Gipsy
image processing software), running on a lil' 11/750... 

	If you know of a "modern" rat4 we could get our hands on, I would
appreciate it...  I would also appreciate it if someone could tell me if
the above code is necessary in some way that I am not thinking of?

	Thanks,

-- 
			Brad Banko
			...!decvax!cwruecmp!ncoast!btb
			Cleveland, Ohio

Re: better ratfor ?

#4444

Author: Random
Date: Thu, 20 Nov 1986 14:01

13 lines
1135 bytes

At a place I used to work, we had some ratfor programs. A guy there modified
the RatFor preprocessor (compiler) to detect the special case loop of

	for (i=x; i<y; i=i+z) 

This was converted in a VMS FORTRAN do loop instead of if's and goto's. This
allowed the fortran compiler to detect that a loop was present and kick
in loop optimizing code. I don't remember the numbers, but the improvement
was significant.
-- 
					Random (Randy Buckland)
					Research Triangle Institute
					...!mcnc!rti-sel!rcb

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