Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!pasteur!ucbvax!agate!shelby!portia!edgar
From: edgar@portia.Stanford.EDU (Edgar Holmann)
Newsgroups: comp.sys.mips
Subject: Redefinition of left shift operator
Message-ID: <4724@portia.Stanford.EDU>
Date: 22 Aug 89 20:37:33 GMT
Sender: Edgar Holmann <edgar@Portia.stanford.edu>
Reply-To: edgar@Neon.Stanford.EDU (Edgar Holmann)
Distribution: usa
Organization: Stanford University
Lines: 22


Has the left shift operator been redefined in the MIPS systems from the typical
shift to a modulo type shift?  By this I mean:
   i << j
redefined to
   i << (j % 32)
This is evident when you shift by a quantity larger than or equal to the int
size (32).  When j is a constant, the compiler issues a warning message (when
using the optimizer level 2 or 3).  Now, I see that nobody should be shifting
by a constant larger than 32 but what about shifting by another variable when
creating a mask?  Thus, a simple statement of the form
   (1L << j) - 1
or
   ~(~0 << j)
now has to have a conditional to handle the case when j is 32.  I have tried
this on an R3000 running Ultrix 3.1 with cc1.31.  The same result is obtained
in an R2000.

Is this considered a "feature" of the mips compiler or is it something that
will get changed in a new release?

edgar