Newsgroups: comp.arch
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: COBOL Decimal Arithmetic
Message-ID: <1989Sep24.003602.7988@utzoo.uucp>
Organization: U of Toronto Zoology
References: <943@rd1632.Dayton.NCR.COM>
Date: Sun, 24 Sep 89 00:36:02 GMT

In article <943@rd1632.Dayton.NCR.COM> otto@rd1632.UUCP (Jerome A. Otto) writes:
>(2)   Convert to binary (using hardware instructions if
>      available), add binary, convert from binary (using 
>      hardware if available)
>
>Very seldom, if ever, is (2) fastest due to the problem of 
>converting from binary to decimal.  This conversion requires 
>N divides or N+1 multiplies (N = number of digits)...

Nonsense.  The multiplies and divides are done at compile time; the
conversion is done with table lookup or the decision-tree equivalent.
Even the simplest approach requires roughly 4N comparisons, a bit of data
movement, and no multiplies or divides at all.  Byte-at-a-time table
lookup reduces this nearly to zero.

Agreed, however, that playing tricks with the binary adder is a viable
alternative if very little arithmetic is being done.
-- 
"Where is D.D. Harriman now,   |     Henry Spencer at U of Toronto Zoology
when we really *need* him?"    | uunet!attcan!utzoo!henry henry@zoo.toronto.edu