Re: [Ql-Users] Behaviour of DIV with negative numbers in SBASIC (QPC2)

[Marcel Kilgus]

John Alexander wrote:
> I'm sure it was written in C, I've not seen a dump of that about
> (is there one BTW??)

Why guess, the source code is available on the web. And it is
thousands upon thousands of lines of assembler code.

Marcel

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Re: [Ql-Users] Behaviour of DIV with negative numbers in SBASIC (QPC2)

[John Alexander]

I'm sure it was written in C, I've not seen a dump of that about (is there one 
BTW??) As such an assembly dump of the ROM would be quite different to what was 
originally written.
Could Tony enlighten us on that bit of history? 
Cheers John Alexander 

Sent from Yahoo Mail on Android 
 
  On Wed, 11 Jan, 2017 at 12:51, Marcel Kilgus wrote: 
  Tony Tebby wrote:
> If the divisor is negative, there is a problem. The "Euclidian division"
> definition requires that the remainder be between 0 and |divisor|-1. 
> This would seem to be a rather less than rigorous definition as 
> |divisor| is not a continuous function. In SBASIC the MOD function gives
> a remainder with the same sign as the divisor, which seemed, at the 
> time, to be more conventional, more logical and more useful. This forces
> the use of the "floored division" approach (second graph in the Wiki 
> article Modulo Operation) as described by Tobias. Floored division for
> DIV was not the choice, it was a consequence of the choice made for the
> MOD operation.
>
> Tony Tebby

Always good to hear the back-story to these things, thanks Tony! I've
fixed a minor bug in SBasic a few days ago and I'm simply amazed by
the amount of work that went into that code. Often I have a hard time
understanding halve of it, but I guess after all this time you
wouldn't fare much better? :-)

Cheers, Marcel

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Re: [Ql-Users] Behaviour of DIV with negative numbers in SBASIC (QPC2)

[Marcel Kilgus]

Tony Tebby wrote:
> If the divisor is negative, there is a problem. The "Euclidian division"
> definition requires that the remainder be between 0 and |divisor|-1. 
> This would seem to be a rather less than rigorous definition as 
> |divisor| is not a continuous function. In SBASIC the MOD function gives
> a remainder with the same sign as the divisor, which seemed, at the 
> time, to be more conventional, more logical and more useful. This forces
> the use of the "floored division" approach (second graph in the Wiki 
> article Modulo Operation) as described by Tobias. Floored division for
> DIV was not the choice, it was a consequence of the choice made for the
> MOD operation.
>
> Tony Tebby

Always good to hear the back-story to these things, thanks Tony! I've
fixed a minor bug in SBasic a few days ago and I'm simply amazed by
the amount of work that went into that code. Often I have a hard time
understanding halve of it, but I guess after all this time you
wouldn't fare much better? :-)

Cheers, Marcel

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