From: user5857@newsgrouper.org.invalid   
      
   Thomas Koenig  posted:   
      
   > Robert Finch  schrieb:   
   > > On 2025-11-11 4:18 p.m., Thomas Koenig wrote:   
   > >> Robert Finch  schrieb:   
   > >>> Typical process for NaN boxing is to set the high order bits of the   
   > >>> value which causes the value to appear to be a NaN at higher precision.   
   > >>> I have been thinking about using some of the high order bits of the NaN   
   > >>> (eg bits 32 to 51) to indicate the precision of the boxed value. This   
   > >>> would allow detection of the use of a lower precision value in   
   > >>> arithmetic. Suppose a convert from single to double precision is being   
   > >>> done, but the value to be converted is only half precision.   
   > >>   
   > >> Do you mean a type mismatch, a conversion, or digits lost due to   
   > >> cancellation?   
   > >   
   > > It would be an input type mismatch. >   
   >   
   > I think this can only happen when software is buggy; compilers should   
   > deal with it, unless the user intentionally accesses data with   
   > the wrong type.   
   >   
   > >>> If it were   
   > >>> indicated by the NaN software might be able to fix the result.   
   > >>   
   > >> Fixing a result after an NaN has occurred is too late, I think.   
   > >>   
   > > I suppose the float package could always just automatically upgrade the   
   > > precision from lower to higher when it goes to do the calculation. But   
   > > maybe with a trace warning. It would be able to if the precision were   
   > > indicated in the NaN.   
   >   
   > I have implemented a few warning about conversions in gfortran.   
   > For example, -Wconversion-extra gives you, for the program   
   >   
   > program main   
   >   print *,0.3333333333   
   > end program main   
   >   
   > the warning   
   >   
   >     2 |   print *,0.3333333333   
   >       |                      1   
   > Warning: Non-significant digits in 'REAL(4)' number at (1), maybe incorrect   
   KIND [-Wconversion-extra]   
   >   
   > But my favorite is   
   >   
   >     3 |   print *,a**(3/5)   
      
   BTW, this works in eXcel where 3/5 = 0.6   
      
   AND, in My 66000, a**0.6 is a single instruction. ...   
      
   >       |               1   
   > Warning: Integer division truncated to constant '0' at (1) [-W   
   nteger-division]   
   >   
   > which (presumably) has caught that particular idiom in a few codes.   
      
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