From: stephen@vfxforth.com   
      
   On 5 Mar 2026 at 01:52:06 CET, "Paul Rubin"  wrote:   
      
   > Stephen Pelc  writes:   
   >> The application is construction planning. Sometimes over 10 currencies   
   >> are used. The app must allow for a total cost of well over 10 billion   
   >> dollars US.  They tried 80 bit FP, but the difference in dollars given   
   >> by an 128 bit integer calculation (effectively a huge spreadsheet) and   
   >> an 80 bit floating point version was 10 million dollars for capping   
   >> the piles in the new Hong Kong airport.. There are many examples in   
   >> construction of dealing with two quantities, one of which is large and   
   >> the other small. Capping piles is one of these.   
   >   
   > I wonder if this was due to some kind of numerical instability in which   
   > case 128 bits might not be enough either.  80 bit FP has a 53 bit   
   > mantissa and 2**53 pennies is 9e15 dollars.  Did you try the same   
   > calculation with say 256 bit FP, bignums, or whatever?   
      
   128 bit ints were good enough. We could probably have got away with 96 bits   
   but 128 bits were as easy. Note that this is a production app. Speed was also   
   important. Porting the system from ProForth for Windows (a DTC Forth) to VFX   
   Forth (native code compilation) gave a factor of ten improvement in   
   recalculation speed.   
      
   Stephen   
      
   --   
   Stephen Pelc, stephen@vfxforth.com   
   Wodni & Pelc GmbH   
   Vienna, Austria   
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