Author: Chan Rasjid
Date: 00:29:48 01/18/06
Go up one level in this thread
On January 17, 2006 at 17:41:03, James Swafford wrote: >On January 17, 2006 at 14:59:15, Robert Hyatt wrote: > >>On January 17, 2006 at 12:52:40, James Swafford wrote: >> >>>On January 17, 2006 at 12:29:21, JW de Kort wrote: >>> >>>>Thank you for your reply. I check the boundries of the array's but that seems to >>>>be correct. >>>> >>>>Could you please clarify your response because i'am not 100% sure what you mean. >>>> >>> >>>I'll try. Let me preface this with this caveat: I doubt this is >>>your problem. :) Dann's advice is pretty sound. >>> >>>Let's say you are evaluating a bitwise expression "a & b". >>>If a == 0, then ( a & b ) == 0 for any b. So, it's not >>>necessary for the compiler to go to the trouble of figuring >>>out what b is. >>> >>>In your case, a & b represent items in an array. What is >>>really evaluated is probably implementation specific >>>(depends on the compiler), but it wouldn't even need to fetch >>>the item from the second array to do the bitwise comparison >>>if your first item (a) is 0. So, possibly you are skirting a >>>boundary bug when i==1 since your "a" is always 0. >>> >>>Again, I doubt that's the case in your program, but it's >>>a possiblity. >>> >>>-- >>>James >>> >> >>I don't see how that would cause a problem, since it has to fetch both values, >>and then AND them to produce the final zero/non-zero result for testing. This >>isn't the same as > > > >Why does it have to? If you say that's what most compilers *do*, then >I believe you (I don't claim to be a compiler expert), but, mathematically, >they don't *have to*, since 0 & b == 0 for any integer b. >Please tell me what I'm missing. :) >James I can guess compiler has to have a natural degree of dumbness. You specifically ask to test if ( (a & b)== 0 ). I doubt they do extra work to add if (a == 0), ..or if (a == 0) && if (b == 0 ). Rather the expected method is fetch, a, fetch b AND them and test. Rasjid
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