On 14 Jan 2013, at 17:03, Martin wrote:
> On 14/01/2013 15:52, Jonas Maebe wrote:
>>
>> On 14 Jan 2013, at 16:44, Martin wrote:
>>
>>> This is casting a "set of bits" (neither signed, nor unsigned - a set is
>>> not a number at all) into a number. This only needs to have a definition,
>>> if it should cast to signed or unsigned type.
>>
>> It has to be signed, because otherwise any negative number in the operation
>> would trigger a range check error when it gets converted to a (larger)
>> unsigned type. The nature of the operation that is used afterwards is
>> irrelevant, range checking always operates in exactly the same way when
>> performing a type conversion from one type to another. This is required to
>> have predictable behaviour in a programming language.
>
> not sure if I follow. If "or" performs on a "set of bits" (rather than a
> number)
It doesn't operate on a set. The left and right operands are whole numbers, and
hence the operator works on whole numbers and returns a whole number. In
Pascal, sets and whole numbers are completely distinct types with different
operators. There is no magic type conversion from integer to a set and back
just because you use the "or" operator.
Jonas
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