On 01/31/2006 02:37 PM, Howie Goodell wrote:
The test "i<limit" fails where 16-bit math or huge loops hit the signed-arithmetic threshold. Using unsigned arithmetic only buys you another power of 2. The safe approach is to say, "limit-i<1".
Oh, sure. I just didn't want to complexificate the example by introducing issues of machine representation and wraparound, let alone handling signalling NaNs or sign extension.
"i<>0" fails much more insidiously if your language only has floating point variables. Then "i=limit" might *never* be true, depending on how it was calculated, or else fail sporadically. I once used an environment where the multitasker saved only 64 bits of floating-point numbers, not the 80x86 FPU's 80 bits. So equality tests worked as expected *almost* always, except for rare combinations of iterator value and thread synchronization.;-(
<python-mode accent="Yorkshire"> Well, *I* once worked with a system that obliged you to push numbers onto a stack, but the garbage collector might fire mid-push, and happily collect the very number you were pushing, precisely because the only reference to it was in a CPU register, leaving you with a lovely new reference to anything at all, except your number. So a program would work >>99% of the time, and then go all doo-lally, usually when a manager was looking. And the problem wasn't in your source, so there was no point looking there to find it. I had to get up two hours before I went to bed to find that bug, and my boss had me executed even though it wasn't in my code. Kids today, don't know they're born. </python-mode>
I propose that the answer to "Should we teach better or use safer programming constructs?" is also, "Yes." I'm revising an embedded end-user programming environment now. This thread just convinced me to add "foreach" to it.;-)
There's nothing quite like creating tools for other programmers whose code will then be burned into ROMs. (Four such ROMs of mine are on eBay now. I am not making this up.) The answer to: "does this concentrate the mind wonderfully, or drive you potty?" is "Yes." Plus, you learn how to dodge missiles thrown from nearby desks, a valuable skill that is sadly neglected in our schools since I left them. -- Frank Wales [EMAIL PROTECTED] ---------------------------------------------------------------------- PPIG Discuss List (discuss@ppig.org) Discuss admin: http://limitlessmail.net/mailman/listinfo/discuss Announce admin: http://limitlessmail.net/mailman/listinfo/announce PPIG Discuss archive: http://www.mail-archive.com/discuss%40ppig.org/
