Re: 0.3-0.2=0.999999999998?

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#16380

From: Tor Iver Wilhelmsen
Date: Fri, 05 Mar 1999 00:00

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roedy@mindprod.com (Roedy Green) writes:

> I disagree.  Binary arithmetic is faster and simpler.  The repeaters
> just move to different places.  You can't get rid of them.  If you
> want absolute precision, use scaled integer arithmetic which is many
> times faster that floating point (e.g. integer pennies for currency,
> with a decorative decimal point inserted for display).

Yes, but even slow 8-bit CPUs in the late seventies had a "binary
coded decimal"-mode which fit two decimal digits into a byte, using a
nibble (that's four bits, young'uns) for each. (That is, the decimal
number 42 was encoded as the hex number 0x42). Adding 1 to 0x99 thus
yielded 0x00 and carry/overflow.

Kinda opens a possibility for maths akin to how BigDecimal and friends
do their stuff - as long as you remembered to adjust your decimal
point correctly.

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From: Tor Iver Wilhelmsen <toriw@online.no>
Subject: Re: 0.3-0.2=0.999999999998?
Date: 1999/03/05
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