Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!rutgers!mit-eddie!uw-beaver!ubc-vision!alberta!teletron!andrew From: andrew@teletron.UUCP Newsgroups: unix-pc.general,comp.sys.att Subject: Re: 3b1 instruction timings Message-ID: <150@teletron.UUCP> Date: Sun, 6-Dec-87 21:18:04 EST Article-I.D.: teletron.150 Posted: Sun Dec 6 21:18:04 1987 Date-Received: Sat, 12-Dec-87 08:47:35 EST References: <787@hsi.UUCP> Organization: TeleTronic Communications Ltd., Edmonton, Alta. Lines: 32 Keywords: 3b1, 7300 Xref: utgpu unix-pc.general:95 comp.sys.att:1749 Summary: 68000 coding tips In article <787@hsi.UUCP>, stevens@hsi.UUCP (Richard Stevens) writes: > While trying to hand optimize some C code for a graphics routine > that I wanted to get as fast as possible, I performed some > timings on the 3b1. > I used the cc optimizer for all timings. A couple of observations: > - stick to shorts instead of ints or longs, when possible, since > a 32-bit multiply or divide gets very expensive. This holds true for array indices as well. Using a short as an array index results in the 68000 muls.w or mulu.w instruction being used for the address calculation instead of the more expensive 32 bit multiplication subroutines used for ints or longs. > - registers don't buy you much except for adds and subtracts (and > assignments too, I'd guess). Actually, register variables buy you a *lot* in most code. The 68000 family was designed so that register usage makes code sing. I would *highly* recommend register variables for heavily used pointer variables (such as in string processing or structure access routines). > Overall I wasn't very impressed with the code quality of the C compiler, > even with the optimizer. Me either. Andrew Scott (..alberta!teletron!andrew) TeleTronic Communications Ltd.