Re: [Bug: 21.4.19] Bruised floating point numbers from string-to-int

Raymond> If you don't get 1.0, you have a badly broken system, if Raymond> you are using IEEE 754. 0.125 and 0.875 can be Raymond> represented exactly, and so can their sum. If you don't Raymond> get 1.0, then your reader is broken or your printer. Or, Raymond> perhaps, + is broken. :-) But what if I get 1.000? Where is something broken? My point is that a conscientious human presented with the problem 0.125 0.125 0.125 0.125 0.875 0.875 0.875 0.875 ----- ----- ----- ----- will almost certainly complete it with 0.125 0.125 0.125 0.125 0.875 0.875 0.875 0.875 ----- ----- ----- ----- 1.000 1.000 1.000 1.000 not 0.125 0.125 0.125 0.125 0.875 0.875 0.875 0.875 ----- ----- ----- ----- 1.0 1.0 1.0 1.0 And surely that's what Rodney wants, too! No? sjt> Yup. `string-to-int' is an alias for `string-to-number', sjt> which is (ultimately) just a wrapper around the platform's sjt> printf implementation. sjt> What you get is what you get. Raymond> But it is possible to do a better job. Raymond> CMUCL prints "8.18e-1" exactly like that. Which is *arguably wrong* because you've lost a digit of precision. I really don't think *Rodney* can win this way. Yes, *we* could get prettier output for the occasional number, but he's working with tables. Raymond> Perhaps printf/scanf doesn't use those algorithms. Microsoft's apparent do, Unices don't. Not worth our effort to replace them, I suggest, unless somebody != me :-) wants to look up the various algorithms *and* present the rationales, *and* document the algorithms so people know what to expect, *as well as* update our test suite. Without that, we're really no better off than we are at present, are we? People are still going to be surprised by the output they get (although in most cases pleasantly so :-). What is it that makes avoiding `format' worth all that? (That's an honest question, not a put-down.) -- School of Systems and Information Engineering http://turnbull.sk.tsukuba.ac.jp University of Tsukuba Tennodai 1-1-1 Tsukuba 305-8573 JAPAN Ask not how you can "do" free software business; ask what your business can "do for" free software.