[Gambas-user] Rol/Ror vs. Shl/Shr

[Benoit Minisini]

Le Jeudi 12 Juin 2003 04:08, Rob a écrit :
> I was trying to come up with some examples for Rol/Ror tonight (bit rotate
> left/bit rotate right) and an explanation for the differences from Shl/Shr,
> so I made a simple console only project and put this in sub main:
>
>   DIM oldvar AS Byte
>   DIM newvar AS Byte
>
>   oldvar = 129
>   newvar = Shl(oldvar,1)
>   PRINT newvar
>
>   newvar = Rol(oldvar,1)
>   PRINT newvar
>
> and built and ran it, and got this:
>
> 2
> 2
>
> meaning Shl and Rol both treat carried bits the same (discard them).  Are
> they meant to just be aliases of each other or is this a gambas bug?
>
> For what it's worth, changing them to Shr and Ror returned
> 64
> 64
> which is consistent, but when I made newvar an Integer, it returned
> 64
> -2147483584
> which is more what I'd expect (the latter being the output of Ror.)  I
> noticed there were no examples for Rol/Ror in the encyclopaedia and figured
> maybe it was something Benoit meant to fix a long time ago and got
> distracted by more interesting things ;)
>
> Rob
>

Hum... In fact these functions work only with full integers, because they 
don't manage the case where their arguments are less than 4 bytes integers.
Call this a bug !

-- 
Benoit Minisini
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