[Cuis] VM Bug

[Juan Vuletich]

Hi Ken,

On 2/22/2013 2:04 AM, Ken Dickey wrote:
> I have been using Pharo-2.0's one-click cog VM with Pharo.
>
> There appears to be a bug in ShortIntegerArray on Linux (not tested on other platforms) such that you can't store 16-bit values iff the high bit is set.
>
> Not a problem for most of you, but I was using ShortIntegerArray-s to hold Unicode code points.
>
> http://code.google.com/p/pharo/issues/detail?id=7569
>
> FYI,
> -KenD

Cuis with Cog on my Mac shows same behavior. So I digged a little bit. 
It is not a bug. ShortIntegerArray handles 16-bit unsigned integers. I 
corrected the class comment. I.e.:

"ShortIntegerArray : unsigned"
sia := ShortIntegerArray new: 8 withAll: 0.
sia at: 1 put: 16r8421.        "fails"
sia at: 1 put: -16r8000.    "ok"
sia at: 1.

"IntegerArray : signed"
ia := IntegerArray new: 8 withAll: 0.
ia at: 1 put: 16r84210000.      "Converts to negative"
ia at: 1.
ia at: 1 put: -16r80000000.    "ok"
ia at: 1.

"WordArray: unsigned"
wa := WordArray new: 8 withAll: 0.
wa at: 1 put: 16r8421.                    "ok"
wa := WordArray new: 8 withAll: 0.
wa at: 1 put: -1.

Note that WordArray stores unsigned numbers, but the primitives handle 
signed. If you want unsigned 16 bit, I'd rather add #unsignedAt: and 
#unsignedAt:put: to ShortIntegerArray, doing a conversion like WordArray 
does.

Cheers,
Juan Vuletich