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From: barmar@think.COM (Barry Margolin)
Newsgroups: comp.lang.c,comp.misc
Subject: Re: 32bit = 16bit x 16bit (Really: Compiler deficiencies)
Message-ID: <10621@think.UUCP>
Date: Thu, 29-Oct-87 18:17:58 EST
Article-I.D.: think.10621
Posted: Thu Oct 29 18:17:58 1987
Date-Received: Tue, 3-Nov-87 06:08:36 EST
References: <141@kesmai.COM> <7349@alice.UUCP> <146MAXHAM@RICE> <593@l.cc.purdue.edu> <120@babbage.acc.virginia.edu>
Sender: usenet@think.UUCP
Reply-To: barmar@pozzo.UUCP (Barry Margolin)
Organization: Thinking Machines Corporation, Cambridge, MA
Lines: 27
Xref: mnetor comp.lang.c:5204 comp.misc:1551

In article <120@babbage.acc.virginia.edu> mac3n@babbage.acc.virginia.edu (Alex Colvin) writes:
>In article <593@l.cc.purdue.edu>, cik@l.cc.purdue.edu (Herman Rubin) writes:
>> 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.

PL/I's default is to do just this!  And if you multiply "fixed bin
(12,5)" (12 bits with 5 after the binary point) by "fixed bin (16,3)"
the default result is "fixed bin (28,8)".  Imagine -- a language that
follows the rules for arithmetic that we learned in grade school!  For
cases where you know that the result will not be the default (usually
when one of the operands is a literal, and the automatically-generated
data type isn't appropriate), there is a version of the multiplication
operator that lets you specify the size of the result:

	result = multiply (var, 3, 16, 3);

which means "multiply var by 3 giving a sixteen-bit result with three
bits after the binary point)."

---
Barry Margolin
Thinking Machines Corp.

barmar@think.com
seismo!think!barmar