[fpc-devel] Do bitwise operation (1 or 2) acre about the sign ? (Giving sign related hints on compilation)

[Jonas Maebe]

On 14 Jan 2013, at 14:54, ik wrote:

> On Mon, Jan 14, 2013 at 3:11 PM, Martin <lazarus at mfriebe.de> wrote:
>> Having recently asked about and learned that it is mainly a hint  
>> about
>> performance. I have now another question about this hint:
>>  project1.lpr(6,9) Hint: Mixing signed expressions and longwords  
>> gives a
>> 64bit result
>>
>> Actually not so much about the hint, as about the fact that in the  
>> below
>> example fpc extends the operands to 64 bits.
>>
>> program Project1;
>> var
>>  x: cardinal;
>>  i, j: integer;
>> begin
>>  i:= x or j
>> end.
>>
>> I understand the need for a 64 bit operation for +/-/</>/*/...
>>
>> But the "or" operator works bitwise, it does not treat the operands  
>> as
>> numbers which could either be signed or unsigned? Or does it? If it  
>> does
>> not, why does it need to use 64 bit?
>
> i is an "integer" type, and you try to assign it a number that might
> have 64 bit value.
> It might overflow the memory itself.

And as an addendum to my previous mail, related to the above: in case  
range checking is on, then the widening will not be removed and the  
full (signed) 64 bit value will be range checked against the type of  
the variable to which the result is assigned.


Jonas