Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site ncrcae.UUCP Path: utzoo!linus!decvax!mcnc!ncsu!ncrcae!wescott From: wescott@ncrcae.UUCP (Mike Wescott) Newsgroups: net.lang.c Subject: Re: Re: Casting Pointers -- fast *portab - (nf) Message-ID: <2011@ncrcae.UUCP> Date: Mon, 20-Feb-84 22:43:10 EST Article-I.D.: ncrcae.2011 Posted: Mon Feb 20 22:43:10 1984 Date-Received: Wed, 22-Feb-84 04:29:25 EST References: <2482@fortune.UUCP> Organization: NCR, Columbia, SC Lines: 27 [] > And of course (?) everyone knows by now (?) that you can get even better > with a 68000 by using the move-multiple-long (register load/store) > instructions to eat and spew big gulps. > . > . > . > (See the code for "blt" that comes with the the MIT "C" compiler.) You can also get into trouble if you're not careful. The version of "blt" we used here worked just fine, until it pointed out a microcode bug in the MC68000 for us. The movem instruction, when fetching from memory into registers does an extra word read. The extra word is thrown away and causes no problems, except when the extra read crosses into an unreadable segment, in which case you get an unwanted "segmentation violation" or "panic: kernel memory management error." The situation shows up (if my memory is correct), when the length of the move is a multiple of 48 bytes and abuts an unreadable segment ("blt" uses a 12 register movem). I recoded it and still managed to pick up a little performance. -Mike Wescott NCR Corporation, W. Columbia SC mcnc!ncsu!ncrcae!wescott