Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!inuxc!iuvax!iucs!bobmon From: bobmon@iucs.UUCP Newsgroups: comp.lang.c Subject: Re: Style [++i vs i++] Message-ID: <4594@iucs.UUCP> Date: Wed, 8-Jul-87 23:36:22 EDT Article-I.D.: iucs.4594 Posted: Wed Jul 8 23:36:22 1987 Date-Received: Sat, 11-Jul-87 15:58:13 EDT References: <8213@brl-adm.ARPA> Reply-To: bobmon@iucs.UUCP (Che' Flamingo) Organization: Camo Flamingo Liberation Affront Lines: 16 escott@BONNIE.UCI.EDU (Scott Menter) writes: > >Actually, I once used a compiler (I don't remember which; maybe it was the >os9 level II 6809 compiler) where "i++" and "++i" compiled into slightly >different code. Apparently the instruction set had a "post-increment" and >"pre-decrement" addressing mode (macro-11 has this too, unless I'm mistaken). >So, if you used pre-auto-decrement ("--i"), or post-auto-increment ("i++"), >you had the advantage of this addressing mode. [...] PDP-11's (Macro-11), 6809's, 6502's and 680x0's all feature post-increment and pre-decrement addressing modes. However, since the inc/decrement of the relevant index register is a side effect of some instruction that's USING that addressing mode, it isn't obvious to me that the use of that mode is exceptionally efficient when the side effect is all you want. Nor is it obvious to me that all compilers would pick up on this "optimization" (although I'm sure that some do).