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Re: double to string????

To: REALbasic NUG <realbasic-nug@lists.realsoftware.com>
Subject: Re: double to string????
From: William Squires <wsquires@satx.rr.com>
Date: Mon, 30 Jun 2008 20:27:15 -0500
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On Jun 30, 2008, at 2:02 PM, Markus Winter wrote:

v as double
v = 12345678901234567890.1234567890

EF1.text = Format(v,
"-
#########################################################.########## ##
####
######################################")

produces

12345678901234567168.

Markus, a double only offers, I believe, 17 digits of accuracy. You
have exceeded that by a long shot. To handle a number like that would
require a double double, a 16 byte double I believe. There is someone
who offers an RB package that gives you basically unlimited number
sizes as well as a ton of other mathematics but I cannot remember the
authors name or the name of the package that he offers. I am sure
someone else will remember.

I think a double should easily hold a 20 digit number. Otherwise it would be
the worst implementation in any programming language ever.

Totally untrue. I believe the (bit) format of a double is specified by some IEEE standard. Bit 63 is the sign bit (of the mantissa, I believe), then you have some bits for the exponent (which has an integral value from -308 to +308, IIRC), then the remaining bits for the mantissa. No matter how you stir it, you have to sacrifice something to get a good dynamic range for both the mantissa and exponent values. I believe that most FP instructions (with the exception of the Moto 68k series) in microprocessors today conform to this standard, but I could be wrong.



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