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Postings from December 2013
On Tue, 17 Dec 2013 13:02:19 +0100, Zefram <zefram@fysh.org> wrote: > Christian Walde wrote: >> I do think that, instead of forcing people to do `sp -= items;` just >> to be able to iterate forwards through arguments with ++, someone >> would probably have instead just made a macro that points to the >> start of the arguments in the stack. > > This is one of the things that arises from efficiency concerns. > You could replace sp[3] (used after sp-=items) with sp[3-items] (with no > decrement of sp), but it's a more complex expression, which depending > on CPU architecture may take longer to execute. (It'll be the same on > current x86 CPUs.) The decrement also gets you into the right place to > start pushing return values. Decrementing sp is part of the stereotyped > variable use that you'd likely reinvent, at least for variadic xsubs. After explaining in #p5p that outputs need to replace the inputs on the stack, this all makes a lot more sense. Steffen, you probably want to mention this fact early on in your article so the rest is more self-explanatory. :) -- With regards, Christian WaldeThread Previous | Thread Next