From: sfuld@alumni.cmu.edu.invalid   
      
   On 11/4/2025 7:19 AM, Scott Lurndal wrote:   
   > Michael S  writes:   
   >> On Mon, 03 Nov 2025 15:22:44 GMT   
   >> scott@slp53.sl.home (Scott Lurndal) wrote:   
   >   
   >>> By decimal FP, do you mean BCD?  I.e. a format where   
   >>> you have a BCD exponent sign digit (BCD 'C' or 'D')   
   >>> followed by two BCD exponent digits, followed by a   
   >>> mantissa sign digit ('C' or 'D') followed by a variable   
   >>> number of mantissa digits (1 to 100)?   
   >>   
   >> I am pretty sure that by decimal FP Terje means decimal FP :-). As   
   >> defined in IEEE 754 (formerly it was in 854, but since 2008 it became a   
   >> part of the main standard).   
   >> IEEE 754 has two options for encoding of mantissa, IBM's DPD which is   
   >> a clever variation of Base 1000 and Intel's binary.   
   >> DPD encoding is considered preferable for hardware implementations   
   >> while binary encoding is easier for software implementations.   
   >> BCD is not an option, it's information density is insufficient to   
   >> supply required semantics in given size of container.   
   >   
   > How so?  The B3500 supported 100 digit (400 bit) signed mantissa and   
   > a two digit signed exponent using a BCD representation.   
      
   By "information density" I think he means that for almost any (I won't   
   say any because there might be some edge cases where the isn't true)   
   value, it takes fewer bits to represent in the IEEE scheme than in your   
   beloved Burroughs Medium system's scheme.  :-)  Fewer bits per value   
   means higher information density.   
      
   Fewer bits means less less hardware, thus lower cost, less power   
   required, etc.   
      
      
   --   
     - Stephen Fuld   
   (e-mail address disguised to prevent spam)   
      
   --- SoupGate-Win32 v1.05   
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