Re: difference between ~0U and ~0

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Date	Fri, 09 Mar 2012 18:52:08 -0500
From	pete <pfiland@mindspring.com>
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Tim Rentsch wrote:
> 
> pete <pfiland@mindspring.com> writes:
> 
> > James Piper wrote:
> >>
> >> On Thursday, March 8, 2012 8:55:20 AM UTC-5, pete wrote:
> >> > somenath wrote:
> >> >
> >> > > According to my understanding ~0 is -1.
> >> > > So I will get all bit 1 as a
> >> > > result of ~0 in 2's complement system.
> >> >
> >> > Close, but backwards.
> >> >
> >> >     ~0 is all bit 1.
> >> >
> >> >     So you will get -1 as a
> >> >     result of ~0 in 2's complement system.
> >> That's true.
> >>
> >> 1 in 8-bit format is: 0000 0001
> >> To get neg- 1:
> >> 1. Negate bits. 1111 1110
> >> 2. Add 1: 1111 11111
> >>
> >> Same results regardless of the bit size.
> >
> > Another way for negatising in two's complement is:
> > 1. subtract 1. 0000 0000
> > 2. Negate bits: 1111 11111
> >
> > I've worked on assembly code
> > that had it done either way in different parts of the code.
> > I don't know if it was done by the same person.
> 
> The first method turns x into -x;  the second turns -x into x.

I'm not going to dignify that with a response.

Wait, I told that wrong ...

-- 
pete

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difference between ~0U and ~0 somenath <pal_somenath@emc.com> - 2012-03-03 20:03 -0800
  Re: difference between ~0U and ~0 Stephen Sprunk <stephen@sprunk.org> - 2012-03-03 22:55 -0600
  Re: difference between ~0U and ~0 BGB <cr88192@hotmail.com> - 2012-03-03 23:01 -0700
  Re: difference between ~0U and ~0 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-03-04 12:50 +0000
  Re: difference between ~0U and ~0 pete <pfiland@mindspring.com> - 2012-03-08 08:55 -0500
    Re: difference between ~0U and ~0 James Piper <usenet@jamespiper.com> - 2012-03-08 06:52 -0800
      Re: difference between ~0U and ~0 pete <pfiland@mindspring.com> - 2012-03-09 17:53 -0500
        Re: difference between ~0U and ~0 Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-09 15:11 -0800
          Re: difference between ~0U and ~0 pete <pfiland@mindspring.com> - 2012-03-09 18:52 -0500

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