Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ncar!cruff From: cruff@ncar.ucar.edu (Craig Ruff) Newsgroups: comp.sys.m68k Subject: Re: Why does addq.w #n,sp work? Keywords: C asm addq Message-ID: <1110@ncar.ucar.edu> Date: 9 Dec 88 19:00:26 GMT References: <5005@bsu-cs.UUCP> <5460@cbmvax.UUCP> <1100@ncar.ucar.edu> <23329@cornell.UUCP> Reply-To: cruff@handies.UCAR.EDU (Craig Ruff) Distribution: na Organization: Scientific Computing Division/NCAR, Boulder CO Lines: 20 In article <23329@cornell.UUCP> rbrown@svax.cs.cornell.edu (Russell Brown) writes: >>The other reason that everyone seemed to miss is that this method saves >>2 bytes. ... > Untrue. The addq instruction has its data in the instruction word. >It can only be used to add values 1 thru 8, so it only needs 3 bits. That's >why people use it. No, it is true. Compare: addq.w #8, a7 (2 bytes) add.w #8, a7 (4 bytes) add.l #8, a7 (6 bytes) That's also why you'll see values > 8 using add.w instead of add.l. -- Craig Ruff NCAR INTERNET: cruff@ncar.UCAR.EDU (303) 497-1211 P.O. Box 3000 CSNET: cruff@ncar.CSNET Boulder, CO 80307 UUCP: cruff@ncar.UUCP