Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.misc
Subject: data types for money (was Who uses BASIC these days)
Message-ID: <17661@mimsy.UUCP>
Date: 22 May 89 00:38:47 GMT
References: <11581@well.UUCP> <960018@hpclskh.HP.COM> <832@cbnewsc.ATT.COM> <10499@ihlpb.ATT.COM>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 34

In article <10499@ihlpb.ATT.COM> res@ihlpb.ATT.COM (Rich Strebendt) writes:
>Use of integers (even considering only the case of US money amounts) to
>scale money to cents (eg: $100 = 10000 cents) limits you to values
>less than about $43 million.

No: if you use unsigned or, more likely, signed, 16 bit arithmetic, the
limits are 655.35 and 327.67 respectively; if you use 32 bit arithmetic,
the limits are 42 949 672.95 and 21 474 836.47; but if you see reason
and use 128 (or---if you really need them---256) bit integers, the limits
are (signed only) 170141183460469231731687303715884105727 and
57896044618658097711785492504343953926634992332820282019728792003956564819967
cents respectively.

>... (the value of stock shares to five decimal places, for example)

... can be up to 10^33 with only 16 bytes.  (You only get 10^27 with BCD.)
For dollars, a mere 64 bit integer can easily hold the U. S. national
debt (in pennies).  You need 15 digits to count (in pennies) to $2 trillion,
which also takes eight bytes.

>Floating point, of course, avoids the above problem, but suffers from loss of
>precision as the poster above points out.  Loss of precision can be disastrous
>when dealing with other people's money!!!

Indeed.

>The way commercial data processing machines and languages solved this problem
>was through the use of (to use IBM terminology) packed decimal representations
>and arithmetic units.

... which is slower than large-field binary arithemetic.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris