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From: tmoran@bix.com
Subject: Re: fixed point vs floating point (When do you use it ?)
Date: 1997/11/28
Message-ID: <65nafe$u8@lotho.delphi.com>#1/1
X-Deja-AN: 293479075
Organization: Delphi Internet Services <http://www.delphi.com/>
Newsgroups: comp.lang.ada
Date: 1997-11-28T00:00:00+00:00
List-Id: <comp.lang.ada>


In <dewar.880662487@merv> Robert Dewar said:
>In practice all stock values will be model numbers of any reasonable
>floating-point type, so the issue of accurate representation does not
>arise. What is important is the computations that you propose to perform
>on these values. I would guess that for most purposes, it is better to
>use floating-point for stock prices than fixed-point (of course if you

  1) Soon stock prices will be in decimal, and thus not accurately
representable by binary floating point types.  That's already the case for
various commodity prices.  2) For a historical price database, space
matters, and fixed point types, depending on the compiler, are in this
case easier to store in a substantially smaller number of bytes.  (As I
recall, there's only one stock price that doesn't fit in 16 bits with a
delta, and small, of 1/8, not counting adjusting the historical record for
splits etc.) 3) This database was already in this form.  4) Most of the
processing of data of this sort is comparisons, multiplication or division
by integers, or addition/subtraction.  Division of one stock price by
another is relatively rare, and thus not timing critical, and
multiplication of two stock or commodity prices together is even rarer.
So any speed advantage of */ fpt on some new machines is not usually
important.