[Vm-dev] Interpreter>>signed32BitValueOf: and signed64BitValueOf: broken

[Andreas Raab]

Hi -

I just noticed hat Interpreter>>signed32BitValueOf: and 
signed64BitValueOf: are broken for edge cases. The following example 
will illustrate the problem:

array := IntegerArray new: 1.
array at: 1 put: 16rFFFFFFFF. "should fail but doesn't"
array at: 1. "answers -1 incorrectly"

array := IntegerArray new: 1.
array at: 1 put: -16rFFFFFFFF. "should fail but doesn't"
array at: 1. "answers 1 incorrectly"

The problem is that both signed32BitValueOf: as well as 
signed64BitValueOf: do not test whether the high bit of the magnitude is 
set (which it mustn't to fit into a signed integer). The fix is trivial 
in both cases - basically all that's needed at the end of both functions 
is this:

   "Filter out values out of range for the signed interpretation such as
   16rFFFFFFFF (positive w/ bit 32 set) and -16rFFFFFFFF (negative w/ bit
   32 set). Since the sign is implicit in the class we require that the
   high bit of the magnitude is not set which is a simple test here"
   value < 0 ifTrue:[^self primitiveFail].
   negative
     ifTrue:[^0 - value]
     ifFalse:[^value]

Cheers,
   - Andreas