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Date:	Thu, 20 Jan 2005 10:35:15 PST8
From:	"Steven Levine" <steve53@earthlink.net >
Reply-To:	scoug-programming@scoug.com
To:	scoug-programming@scoug.com
Subject:	SCOUG-Programming: Ongoing

In <200501201805.j0KI5nGI017132@well.com>, on 01/20/05
at 10:05 AM, "Gregory W. Smith" said:

> result = a*b/c
>is not necessarily the same as
> temporary = a*b
> result = temporary/c
>Rounding and truncation of intermediate values can propagate through
>millions of calculations and affect the final result. In the example
>2/3.1, the answer is 0.6 when the result is stored as .
>A difference occurs, however,

Focusing on an implementation detail like the lack or not of machine level
BCD arithemtic obscures the fact that that correct answers are more often
dependent on correct algorithms and understanding the numerical
characteristics than any single hardware feature.

BCD arithmetic does nothing to solve the problem where the same data needs
to processed both as:

sum(a*b)

and

sum(a) * b

Make b something like LA sales tax and make a a sufficiently large set of
purchases and one will get to choose between two answers both of which are
arguably correct. Worse yet, one does not always get to choose a single
implementation from the above.

Steven

--
----------------------------------------------------------------------
"Steven Levine" MR2/ICE 2.60b #10183 Warp4/FP15/14.100c_W4
www.scoug.com irc.fyrelizard.com #scoug (Wed 7pm PST)
----------------------------------------------------------------------

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