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From: tac@cs.brown.edu (Theodore A. Camus)
Newsgroups: comp.lang.c
Subject: shift right arithmetic
Message-ID: <49160@brunix.UUCP>
Date: 6 Sep 90 02:29:50 GMT
Sender: news@brunix.UUCP
Reply-To: tac@cs.brown.edu (Theodore A. Camus)
Organization: Brown University Department of Computer Science
Lines: 27


I would like to do a portable arithmetic right shift in C.


Possible solutions and problems :

1) '>>' will _not_ guarantee the result on a signed argument (ANSI & K&R)

2) dividing by a power of 2 will often compile to arithmetic shifts, but 
   only for the smaller powers of 2, not for the full 2^1 - 2^31 shift range.

3) One could test for a negative argument, and if it was negative, use a
   negate / shift / negate sequence, but there should be a better way.


For most compilers, '>>' will differentiate between signed and unsigned
arguments, but again K&R and ANSI allows it to be implementation-defined.

Any answers ?

        - Ted


  CSnet:     tac@cs.brown.edu                          Ted Camus  
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  "An ounce of example is worth a pound of theory."    Providence, RI 02912