Zero-fill shift

Scott David Daniels Scott.Daniels at Acm.Org
Sat Jun 26 17:58:44 CEST 2004


Eli Stevens (WG.c) wrote:

> Daniel Orner <cs993442 at cs.yorku.ca> wrote:
> 
>>Great, this works. 8-) Unfortunately, I've run into another problem.
>>In the Java algorithm, two integers are added. This often results in
>>an overflow and a negative number, which is the desired result....
>
> But more to the point:  Here's something that will do the trick if your
> overflow isn't ever more than one bit....
And if you want to be able to handle multibit overflow:

     SIGN_BIT = 2 ** 7  # 31 if you prefer 32-bit signed numbers

     def wrap(n):
         if n & SIGN_BIT:
             return n | -SIGN_BIT
         else:
             return n & (SIGN_BIT - 1)

-- 
-Scott David Daniels
Scott.Daniels at Acm.Org



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