Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 beta 3/9/83; site desint.UUCP
Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!sdcrdcf!trwrb!desint!geoff
From: geoff@desint.UUCP (Geoff Kuenning)
Newsgroups: net.lang.c
Subject: Re: C needs BCD -- why BCD?  Accountants!
Message-ID: <222@desint.UUCP>
Date: Sat, 17-Nov-84 19:11:39 EST
Article-I.D.: desint.222
Posted: Sat Nov 17 19:11:39 1984
Date-Received: Mon, 19-Nov-84 03:24:07 EST
References: <105@ISM780B.UUCP> <869@ihuxn.UUCP> <904@umcp-cs.UUCP> <4611@utzoo.UUCP>
Organization: his home computer, Thousand Oaks, CA
Lines: 21

> I have always been surprised that business people didn't just use 64
> bit integers, and keep the amounts in CENTS.  No BCD required, can
> take advantage of nice fast machine instructions, etc.

Primarily because there are *still* relatively few machines that have good
support for 64-bit integers.  The average 32-bitter has 32x32 multiply that
produces 64 bits, and a corresponding 64/32 divide, but other 64-bit math
has to be implemented with "add with carry" instructions.  If I recall
correctly, the 360 didn't even have such an instruction, so you really had
to hack it.  The 2-3 instruction sequences needed to perform 64-bit
arithmetic are not really more efficient than single BCD instructions.
Furthermore, many business programs (e.g., general ledger or accounts
receivable update) have a general model of "read in two fields, add them,
write it out".  You can do a BCD add *much* faster than you can do two
conversions and a 64-bit binary add.  Remember that decimal conversion
inherently involves multiplication and division.
-- 

	Geoff Kuenning
	First Systems Corporation
	...!ihnp4!trwrb!desint!geoff