From: ThatWouldBeTelling@thevillage.com   
      
   Terje Mathisen wrote:   
   > EricP wrote:   
   >> Terje Mathisen wrote:   
   >>> Anton Ertl wrote:   
   >>>> Terje Mathisen  writes:   
   >>>>   
   >>>>> This would have simplified all sorts of array/matrix sw where both   
   >>>>> errors (NaN) and missing (None) items are possible.   
   >>>>   
   >>>> In what ways would None behave differently from SNaN?   
   >>>   
   >>> It would be transparently ignored in reductions, with zero overhead.   
   >>   
   >> There is also the behavior with operators - how is it different from   
   >> xNan?   
   >> xNan behaves like an error and poisons any calculation it is in,   
   >> which is also how SQL behaves wrt NULL values:   
   >>   
   >>    value + xNan => xNan   
   >>    value * xNan => xNan   
   >>   
   >> whereas Null is typically thought of as a missing value:   
   >>   
   >>    value + Null => value?   
   >>    value * Null => 0?   
   >>   
   >> It could also have different operator instruction options that select   
   >> different behaviors similar to rounding mode or exception handling bits.   
   >> All those option bits would take up a lot of instruction space.   
   >   
   > I'm used to the Mill None, where a store becomes a NOP, a mul behaves   
   > like x * 1 (or a NOP), same for other operations.   
   >   
   > Terje   
   >   
      
   How does Mill store a None value if they change to NOP?   
      
   I was thinking of spreadsheet style rules for missing cells.   
   Something that's compatible with dsp's, simd, vector, and gpu's,   
   but I don't know enough about all their calculations to know the   
   different ways calculations handle missing values.   
      
   And there can be different None rules just like different roundings.   
      
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