Re: [netcdfgroup] [EXTERNAL] Quantize Support in netCDF-Fortran: Only Bit Groom possible?

  • To: Charlie Zender <zender@xxxxxxx>
  • Subject: Re: [netcdfgroup] [EXTERNAL] Quantize Support in netCDF-Fortran: Only Bit Groom possible?
  • From: "Baker, Lawrence M" <baker@xxxxxxxx>
  • Date: Mon, 7 Nov 2022 22:03:43 +0000
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Charlie,

IEEE
format implicitly defines the first significant bit as 1.

This is true only for normalized IEEE format.  Numbers that are too small to 
represent in the normalized IEEE format use subnormal format.  I do not know 
whether netCDF preserves subnormal numbers 1) in general, or 2) when they are 
compressed.  Whatever the behavior, I recommend it be documented.  (I am not a 
user of netCDF; only an observer of developer conversations.)

Respectfully,

Larry Baker
US Geological Survey (Ret.)
c. 650-784-9650
baker@xxxxxxxx<mailto:baker@xxxxxxxx>



On Nov 7 2022, at 1:54:00 PM, Charlie Zender 
<zender@xxxxxxx<mailto:zender@xxxxxxx>> wrote:



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Hi Matt,

Your understanding of the quantization implementation
is correct on all counts. The actual # of bits per
digit is ln(10)/ln(2) ~ 3.32. And note that netCDF
implementation defines NSB as the number of
_explicitly stored bits_, which is one less than
the number of significant bits because the IEEE
format implicitly defines the first significant bit as 1.
Thus NSB <=23 not <=24.

Charlie
--
Charlie Zender, Earth System Sci. & Computer Sci.
University of California, Irvine 949-891-2429 )'(

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