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From: Lawson.English@p88.f15.n300.z1.fidonet.org (Lawson English)
Newsgroups: comp.sys.mac.programmer
Subject: Re: 68000 Assembly question -- overflow
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Date: 26 May 91 04:38:39 GMT
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Seth Tisue writes in a message to All

ST> Thanks to everyone who straightened me out on this. It still 
ST> seems like a poor situation to have a negative number, -214783648, 
ST> which has no valid corresponding positive representation; I'll 
ST> have my program check for it. (I don't think the user should 
ST> have to worry about taking the negative of something yield an 
overflow.)

Think about it: you have 2^32 numbers available (an even number), this gives
one either an equal number of positive and negative numbers and 2 possible zeros
(one's compliment) or an even number of negative numbers, an odd number of positive
numbers and only one zero (two's compliment). It seems to me that the average
"user" would worry more about the existance of two zeros than about the imbalance
of positive and negative. After all, one might have (and ofen does) a use for
that last odd number, but how many times do you need a second way of representing
"zero?" And for that matter, imagine the headaches of the chip designer who
must add a second test for zero if one's compliment arithmatic were standard.

Lawson
 

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