[Tfug] Speaking of zero...
Paul Scott
waterhorse at ultrasw.com
Mon May 14 14:51:13 MST 2007
William Stott wrote:
> Recently, a conversion on zero was brought up in a class I am taking. The conversation focused on positive and negative values for zero, and what they meant in terms of a computer. Anyone care to throw their ideas into TFUG on this? The instructor said that negative and positive values of zero can cause calculation issues, but he did not elaborate. I am not exactly sure how since the end result seems to be the same. I did see the problem when doing signed magnitude calculations, but only due to the rules in which the book we use gave to us.
>
The beginning is that there are two kinds of hardware even though there
aren't many examples of one of them (one's complement).
1. twos complement: 0 (all bits off) is zero, all bits on is -1.
Lowest possible negative integer is 2**n (n is number of bits) highest
possible positive integer is 2**n - 1
2. ones complement: all bits off is positive zero, all bits on is
negative zero. 2**n - 1 is largest possible integer, - ( 2**n -1 ) is
most negative number.
(** is exponentiation)
The only example I remember of ones complement computers is the CDC 6000
series.
Paul Scott
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