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Groups > comp.sys.acorn.programmer > #5927
| Subject | Re: BASIC oddity? |
|---|---|
| Newsgroups | comp.sys.acorn.programmer |
| From | Alan Adams <alan@adamshome.org.uk> |
| Date | 2020-01-04 16:22 +0000 |
| Message-ID | <a2bf222d58.Alan.Adams@ArmX6.adamshome.org.uk> (permalink) |
| References | (1 earlier) <582cb030b8News03@avisoft.f9.co.uk> <quoa19$o6o$1@dont-email.me> <ef3ac02c58.Alan.Adams@ArmX6.adamshome.org.uk> <qupq4i$4nf$1@gioia.aioe.org> <582d216fd8News03@avisoft.f9.co.uk> |
| Organization | Orpheus Internet Services |
In message <582d216fd8News03@avisoft.f9.co.uk>
Martin <News03@avisoft.f9.co.uk> wrote:
> On 04 Jan in article <qupq4i$4nf$1@gioia.aioe.org>,
> Steve Drain <steve@kappa.me.uk> wrote:
>> druck wrote:
<snip>
> 2. Alan said
>> The weird example is the third, where subtracting a very large
>> positive number from a very large negative number produces a
>> positive result.
> But this result is not weird, it is correct - because as they are
> both UNSIGNED it is subtracting a very large number from an even
> larger number. The result is a small number, which is correct.
> The strange thing about 2's complement arithmetic is that it works
> for both signed and unsigned numbers. The first 4 bytes of a 5-byte
> time block are unsigned, so cannot be regarded as negative. It even
> works when the MSB 5th byte has changed, as the last example shows.
> So, I would suggest that using
> I% = !buf1%
> J% = !buf2%
> K% = I%-J%
> will suffice to calculate a time difference of a few days in cs.
That agrees with what I found. It even seems to work in a case where the
5th (highest) byte is incremented.
The thing I found surprising is that BASIC displays the values in I% and
J% using a signed interpretation, but does the subtraction in an unsigned
fashion. It's this inconsistency that worries me, in case at some future
date is is "corrected".
> ... unless anyone can see the flaws in my argument!
--
Alan Adams, from Northamptonshire
alan@adamshome.org.uk
http://www.nckc.org.uk/
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BASIC oddity? Alan Adams <alan@adamshome.org.uk> - 2020-01-03 17:16 +0000
Re: BASIC oddity? Martin <News03@avisoft.f9.co.uk> - 2020-01-03 19:31 +0000
Re: BASIC oddity? druck <news@druck.org.uk> - 2020-01-03 21:00 +0000
Re: BASIC oddity? Alan Adams <alan@adamshome.org.uk> - 2020-01-03 22:26 +0000
Re: BASIC oddity? Steve Drain <steve@kappa.me.uk> - 2020-01-04 10:40 +0000
Re: BASIC oddity? Martin <News03@avisoft.f9.co.uk> - 2020-01-04 16:08 +0000
Re: BASIC oddity? Alan Adams <alan@adamshome.org.uk> - 2020-01-04 16:22 +0000
Re: BASIC oddity? David Higton <dave@davehigton.me.uk> - 2020-01-04 17:24 +0000
Re: BASIC oddity? Alan Adams <alan@adamshome.org.uk> - 2020-01-04 18:47 +0000
Re: BASIC oddity? Matthew Phillips <spam2011m@yahoo.co.uk> - 2020-01-06 08:58 +0000
Re: BASIC oddity? David Higton <dave@davehigton.me.uk> - 2020-01-06 16:20 +0000
Re: BASIC oddity? Matthew Phillips <spam2011m@yahoo.co.uk> - 2020-01-07 08:49 +0000
Re: BASIC oddity? Martin <News03@avisoft.f9.co.uk> - 2020-01-07 11:20 +0000
Re: BASIC oddity? David Higton <dave@davehigton.me.uk> - 2020-01-07 15:05 +0000
Re: BASIC oddity? Matthew Phillips <spam2011m@yahoo.co.uk> - 2020-01-08 08:23 +0000
Re: BASIC oddity? Alan Adams <alan@adamshome.org.uk> - 2020-01-08 10:26 +0000
Re: BASIC oddity? druck <news@druck.org.uk> - 2020-01-08 21:02 +0000
Re: BASIC oddity? Richard Ashbery <basura@invalid.addr.uk> - 2020-01-09 12:53 +0000
Re: BASIC oddity? Steve Fryatt <news@stevefryatt.org.uk> - 2020-01-09 23:16 +0000
Re: BASIC oddity? Steve Fryatt <news@stevefryatt.org.uk> - 2020-01-08 22:35 +0000
Re: BASIC oddity? Martin <News03@avisoft.f9.co.uk> - 2020-01-08 23:51 +0000
Re: BASIC oddity? Steve Drain <steve@kappa.me.uk> - 2020-01-10 11:30 +0000
Re: BASIC oddity? Alan Adams <alan@adamshome.org.uk> - 2020-01-10 12:38 +0000
Re: BASIC oddity? Jean-Michel <jmc.bruck@orange.fr> - 2020-01-06 20:39 +0100
Re: BASIC oddity? Alan Adams <alan@adamshome.org.uk> - 2020-01-06 21:13 +0000
Re: BASIC oddity? Steve Drain <steve@kappa.me.uk> - 2020-01-08 12:46 +0000
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