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From: cik@l.cc.purdue.edu (Herman Rubin)
Newsgroups: comp.lang.c,comp.misc
Subject: Re: 32bit = 16bit x 16bit (Really: Compiler deficiencies)
Message-ID: <593@l.cc.purdue.edu>
Date: Sat, 24-Oct-87 09:23:25 EST
Article-I.D.: l.593
Posted: Sat Oct 24 09:23:25 1987
Date-Received: Wed, 28-Oct-87 05:25:35 EST
References: <141@kesmai.COM> 7349@alice.UUCP <146MAXHAM@RICE>
Organization: Purdue University Statistics Department
Lines: 30
Summary: This is a problem with HLL
Xref: mnetor comp.lang.c:5147 comp.misc:1531

In article <146MAXHAM@RICE>, MAXHAM@RICE.BITNET (Mark Maxham) writes:
> But the 68000 MULS and MULU commands multiply two sixteen bit words
> into a 32 bit longword.  Thus they are defined.  Is the question
> how C translates from multiplicitive expressions into actual machine
> instructions?
>      
> Mark Maxham      maxham@icsa.rice.edu
>      

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. (Note:  I am using the term "object" because what is
called a word, longword, etc., differs from machine to machine.)  On many
machines, this would have to be done by the portable method of converting
the 16 bit objects to 32 bits, but the possessor of a machine which can do
the operation directly should not have to go to such lengths to achieve the
results.  How about the related problem of multiplying two 32 bit objects and
getting a 64 bit object?  Other than inserting assembler instructions, which
may involve such problems as not knowing where the (expletive deleted) compiler
has decided to locate the objects, I see no way to do this in any HLL.  I know
of no way to tell the compiler that here is an operation with a given syntax,
and the compiler should put it in its set of operations.  If the syntax is
different from other syntaxes for that operator, the compiler should perform
the overloading.  It is clear that the languages need more flexibility
and that the gurus who claim that they have the solutions are wrong.
-- 
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907
Phone: (317)494-6054
hrubin@l.cc.purdue.edu (ARPA or UUCP) or hrubin@purccvm.bitnet