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From: crowl@cs.rochester.edu (Lawrence Crowl)
Newsgroups: comp.arch,misc.wanted,comp.sources.wanted
Subject: Double Width Integer Multiplication and Division
Message-ID: <1989Jun26.195044.4197@cs.rochester.edu>
Date: 26 Jun 89 19:50:44 GMT
References: <57125@linus.UUCP> <1989Jun24.230056.27774@utzoo.uucp> <22218@winchester.mips.COM>
Reply-To: crowl@cs.rochester.edu (Lawrence Crowl)
Organization: U of Rochester, CS Dept, Rochester, NY
Lines: 24

In article <22218@winchester.mips.COM> mash@mips.COM (John Mashey) writes:
>When we were [designing integer division support on the MIPS processors], we
>couldn't think of any languages whose natural implementation on a 32-bit
>machine would expect generation of a 64 by 32 bit divide as the expected
>operation.  Does anybody know of any such, or is this strictly something one
>would use in handcoded routines?
 
Languages which support fixed-point arithmetic, e.g. PL/I and Ada, could use
such a feature to substantially improve fixed-point performance.  In addition,  languages that support a more general notion of integers, such as Lisp bignums 
or declared ranges, can use them to improve the performance on integers larger
than a single word.  There are not a lot of languages currently that support 
such arithmetic, but newer languages are more likely to.
 
Such support is especially crucial for fixed-point arithmetic.  Fixed-point
arithmetic is often a win in both time and precision over floating point.  I
did a Mandelbrot program using fixed-point (via the 68020 32x32->64 multiply)
that was 50% faster than using the FPA on a Sun 3/260 and 480% (5x) faster
than  using the 68881.  However, such advantages cannot be effectively
realized without language support.  Fixed point is generally not used much
because most languages do not support it.
-- 
  Lawrence Crowl		716-275-9499	University of Rochester
		      crowl@cs.rochester.edu	Computer Science Department
...!{allegra,decvax,rutgers}!rochester!crowl	Rochester, New York,  14627