From: bryce@digicash.com
Date: Wed, 22 May 1996 22:51:46 +0800
To: Matts Kallioniemi <matts@pi.se>
Subject: Re: The Crisis with Remailers
In-Reply-To: <2.2.32.19960521175237.0036cc44@mail.pi.se>
Message-ID: <199605220958.LAA16017@digicash.com>
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 Matts Kallionieme <matts@pi.se> wrote:

> At 17:44 1996-05-21 +0200, bryce@digicash.com wrote:
> >Matts, you don't want to do floating point for money, because
> >floating point doesn't give you good control of precision.
> 
> Yes I do. Several major currency traders in Sweden keep all
> their money in 64 bit floating point storage. I think that DigiCash
> will go floating point (get real?) when you start doing currency.
> If you sell 1 DEM, you don't want to get paid in cents, you want
> to get paid in 10-15 decimal places. That's where the currency
> action is right now, and before Ecash(tm) is fully deployed we'll
> probably see traders going for 15-20 decimal places. Floating
> point is the way to do it, but are your accountants ready for it?


Matts, _floating_ point numbers are numbers in which the decimal
place moves ("floats") around depending on the value of the 
number.  Floating point numbers are convenient if you want to 
handle a number that isn't going to be too large, and that isn't
going to need a great deal of precision.  They are _not_ useful 
if you want to handle a number with a lot of precision, nor
indeed, if you want to be able to _know_ the precision!  If you
have a number that represents money, you want to know the 
precision!


As an aside, there are rare cases when you will use a floating point
number to _represent_ a fixed-point number just because the
floating point math is faster on your hardware.  As far as 
I know, this only happens on certain supercomputers.


I shall try to refrain from taking umbrage at your comment that
DigiCash is "not real".  Also that DigiCash doesn't "do"
currency.  What could you possibly mean by that?


> >Keep in mind that only Ecash(tm) Mints can create Ecash(tm) 
> >coins and choose what values the coins have.
> 
> Sorry, I thought that the client created the coins and the mint
> just signed them. I guess I should go back to RTFAPI.


I'm sorry-- I didn't speak clearly.  _Kinds_ of coins, including
such things as the currency and base value (i.e. smallest 
possible coin) are created by Mints.  We call these "coinages".
They are analogous to new kinds of coin or paper notes in 
traditional currency.  The individual coins are generated by the
Ecash(tm) client, but those coins are worthless until they are
stamped by the Mint, giving them a currency and denomination 
(i.e., is this a 5-dollar-cent coin, a 10-dollar-cent coin, a 
100-Finnish-Mark coin, etc.).


For further reading material as well as <a
href="http://www.digicash.com/api"> the API </a>, I can
recommend <a href="http://www.digicash.com/ecash/faq.html"> the
Ecash(tm) FAQ </a>, <a
href="http://www-ugrad.cs.colorado.edu/~wilcoxb/faq"> the Bryce 
(not speaking for DigiCash on these pages) FAQ </a>, the
somewhat out-dated <a
href="http://www.digicash.com/ecash/protocol.html"> Ecash(tm)
protocol description </a>, and Ian Goldberg's <a
href="http://www.cs.berkeley.edu/~iang/ecash/"> Ecash(tm) pages
</a>.


For further reading on floating point and other representations
of numbers in computing, I recommend any good introductory
university text on mathematical computing.  Sorry I don't have
mine handy or I'd give you a specific reference.


Regards,

Bryce

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