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From: mac@harris.cis.ksu.edu (Myron A. Calhoun)
Newsgroups: comp.lang.fortran
Subject: Re: complex*32?
Message-ID: <1990Feb12.140657.28884@deimos.cis.ksu.edu>
Date: 12 Feb 90 14:06:57 GMT
References: <9002120228.AA19489@euler.Berkeley.EDU>
Sender: @deimos.cis.ksu.edu
Reply-To: mac@harris.cis.ksu.edu (Myron A. Calhoun)
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Organization: Kansas State University, Dept of Computing & Information Sciences
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In article <9002120228.AA19489@euler.Berkeley.EDU> ndeng@EULER.BERKELEY.EDU writes:
>
>Is there any machine/compiler in the unix world or IBM world which can handle
>the complex*32 format and can deal with data range of 10e-200 to 10e+200?
                       ^^^
These are UNrelated questions, and the second is easily answered:

10^200 ~= (10^3)^67 ~= (2^10)^67 = 2^670   and   670 < 2^10

Thus any machine which which
  * allocates ten bits (plus a sign bit) to the exponent and
  * uses powers of two for its internal binary representation for
         floating point numbers
or
  * allocates eight bits (plus a sign bit) to the exponent and
  * uses powers of sixteen.....
will handle a range of 10e-200 to 10e+200. 

I've never used one (I can type!-), but I vaguely recall the
Macintosh meets the first set of criteria.  I also recall that
the old IBM 360/370 used powers of sixteen, but only allocated
six bits (plus a sign bit) to the exponent, thus limiting its
range to about
16^64 = (2^4)^64 = 2^256 ~= (2^10)^25.6 ~= (10^3)^25.6 ~= 10^76

Also, I question ANYONE'S need for 32 bytes * 8 bits/byte minus
12 (bits for exponent and two signs) = 244 bits ~= 74 digits
of precision!  If I remember correctly:
   if one knew the value of PI to 50 digits,
   if one knew the radius of the whole universe EXACTLY, and
   if one used both to calculate the diameter of the universe,
   then adding a 51st digit to PI and recalculating the diameter would
        not give a value enough larger to slip a playing card between them.

So I find it hard to believe such precision is necessary.

But I've been wrong before and will undoubtedly be wrong again!
--Myron.
--
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