🚀 go-pugleaf

George Gerrity (gwg@csadfa.oz) writes:

	"... radix 2 or a power thereof has a decided edge over
	decimal.  That is, you can get a better performance with binary
	for a given cost, compared with decimal, or you can achieve a
	fixed performance for a lower cost."

Here's where the argument breaks down.  Binary doesn't necessasrily
give better performance than decimal.  A contrived example:

	dcl gross_income fixed decimal(8,2);
	dcl tax_to_pay   fixed decimal(8,2);
	dcl tax_rate     fixed decimal(3,3);

	tax_rate = .097;	/* tax rate is 9.7% */
	tax_to_pay = gross_income * tax_rate;

To do this last computation using scaled binary, you start with an
integer multiply instruction, giving a result which can be as large as
10^6 (one million dollars) and which is scaled in units of 1/10^5.  You
can't represent this in a 32-bit word, so you go to two 32-bit words.
Then you have to divide by 1000 to re-scale to units of 1/10^2.

Have you priced a division lately?  I'll go a long way to avoid the
need to divide into a 64-bit number.  The RISC chip in my box (an
88100) doesn't do this in hardware, so there I am doing multi-precision
binary division in software -- just the sort of slow, fussy work that I
was supposed to avoid by using binary representations.

  -=- Andrew Klossner   (uunet!tektronix!frip.WV.TEK!andrew)    [UUCP]
                        (andrew%frip.wv.tek.com@relay.cs.net)   [ARPA]