Re: Fun-O Basic Edition Compiler

[Jeffrey Siegal <address@hidden>]

Bruce Hoult wrote:

>>>How can you do it for multiplication, other than by dividing afterwards 
>>>and comparing, or pre-classifying the operands?
>>>
>>Well, sometimes you can preclassify at compile time...
>>
> 
> Yes, if one operand is a constant, k, then you can test the abs() of the 
> other against 2^31/k.

More than that.  I don't know if GD does this, but some compilers 
attempt to classify varibles by range.  So if you know that a variable y 
is between 0 and max and x * max would not overflow, then x * y can't 
overflow either.