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Re: BASIC oddity?

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On 03 Jan in article <4adaa32c58.Alan.Adams@ArmX6.adamshome.org.uk>,
   Alan Adams <alan@adamshome.org.uk> wrote:
> I've either discovered something odd but useful about BASIC, or
> I#ve got myself rather confused.

> The issue arose because I need to subtract one 5-byte time from
> another, returning the result in an integer.

> This will obviously fail if the result is too large to fit in an
> integer, but that is a large number of days, and will not occur in
> my particular case, as the computers will not need to run that
> long without a restart.

> What I thinki I've discovered is that although BASIC treats values
> that go beyone &7fffffff as negative numbers, when suntracting
> them one from another it treats them as unsigned. The following
> example demonstrates why I think this is the case.

> Note that I'm ignoring the MSB of the 5-byte times, as the test was
> created to fnd out what I needed to do with it, and seems to show
> that I simply ignore it.

> The weird example is the third, where subtracting a very large
> positive number from a very large negative number produces a
> positive result.

> Comments please:

I think you are confused. BASIC integers are *always* 4 bytes, never
5 bytes. The statement 
    I%=!buf1%
sets I% to the first 4 bytes at address buf1%

Which I think will explain your results.

There is no way for BASIC to subtract two 5-byte integers, apart from
spliiting each to one 5-byte integer and one 1-bute - and handling
the case where the result is negative. 

However, if the difference is small, or you can ignore the lest
significant byte, you may be able to chose a single 4-bytes that will
provide the difference.

-- 
Martin Avison 
Note that unfortunately this email address will become invalid
without notice if (when) any spam is received. 

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Thread

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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