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From: ram+@cs.cmu.edu (Rob MacLachlan)
Newsgroups: comp.arch
Subject: Re: Compilers and efficiency
Message-ID: <1991Apr9.000144.27650@cs.cmu.edu>
Date: 9 Apr 91 00:01:44 GMT
References: <27fa3350.6bc2@petunia.CalPoly.EDU> <1991Apr5.172533.6717@agate.berkeley.edu> <9782@mentor.cc.purdue.edu>
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Organization: School of Computer Science, Carnegie Mellon
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>From: hrubin@pop.stat.purdue.edu (Herman Rubin)
>Subject: Compilers and efficiency
>Date: 7 Apr 91 19:04:12 GMT
>
>For example, suppose there was an instruction, which could be effectively
>used, which would divide a float by a float, obtaining an integer quotient
>and a float remainder.  Now just how is the compiler to recognize that this
>is in fact wanted?  
>
>There is, at present, no language designed to take into account the collection
>of "natural" useful hardware which the present users can find uses for, and
>which are far more expensive in software than in hardware.

Well, in Common Lisp, (truncate 4.5 2.0) returns 2 (an integer) and .5 (a
float).  And you can use CEILING, FLOOR or ROUND to get rounding to +inf,
-inf or nearest.  The Common Lisp numeric support was designed by someone
with a pretty good understanding of numerical analysis, and of the IEEE
float standard.  [Guy Steele, I believe...]  Unfortunately, most Common Lisp
implementations don't implement numeric stuff well enough to be worth using.
In my work on CMU Common Lisp, I have made some major improvements in basic
efficiency, but nobody has yet realized the full potential of numbers in
Common Lisp.

  Rob