Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!amdcad!ames!ll-xn!husc6!bbn!rochester!PT.CS.CMU.EDU!sei!sei.cmu.edu!firth
From: firth@sei.cmu.edu (Robert Firth)
Newsgroups: comp.lang.c,comp.misc
Subject: Re: 32bit = 16bit x 16bit (Really: Compiler deficiencies)
Message-ID: <2998@aw.sei.cmu.edu>
Date: Mon, 26-Oct-87 17:24:05 EST
Article-I.D.: aw.2998
Posted: Mon Oct 26 17:24:05 1987
Date-Received: Thu, 29-Oct-87 04:43:29 EST
References: <141@kesmai.COM> <7349@alice.UUCP> <146MAXHAM@RICE> <593@l.cc.purdue.edu>
Sender: netnews@sei.cmu.edu
Reply-To: firth@bd.sei.cmu.edu.UUCP (PUT YOUR NAME HERE)
Organization: Carnegie-Mellon University, SEI, Pgh, Pa
Lines: 19
Xref: mnetor comp.lang.c:5158 comp.misc:1535

In article <593@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:
[discussion of 16*16=>32]
>A general problem with HLL's is that they do not have the necessary
>flexibility to handle situations like this.  I do not know of any language
>which has in its operation list an operation to multiply two 16 bit object
>and get a 32 bit object.

The language RTL/2 has exactly this feature; it has versions of "*" that
can multiply integers to give long ints or fractions to give long fracs.

A more modern language that recognises this problem is Ada, which has
explicit features for fixed-point multiplication with double-length
result (hidden in RM 3.5.9,3.5.10), and indeed for "rule-of-three"
operations (multiply to double length; divide back to single length).
These are defined in fairly general terms, and so can be mapped onto
a variety of multiple-length machine types, not just 16 and 32.

The systems language BCPL has an extension that provides the rule-of-three
primitive (called MULDIV), but for integers only.