Bug in floating-point addition: is anyone else seeing this?

[Dave Parker]

On May 21, 12:38 pm, Mark Dickinson <dicki... at gmail.com> wrote:

> >>> a+0.999     # gives expected result
> 9999999999999998.0
> >>> a+0.9999   # doesn't round correctly.
>
> 10000000000000000.0

Shouldn't both of them give 9999999999999999.0?

I wrote the same program under Flaming Thunder:

     Set a to 10^16-2.0.
     Writeline a+0.999.
     Writeline a+0.9999.

and got:

     9999999999999998.999
     9999999999999998.9999

I then set the precision down to 16 decimal digits to emulate Python:

     Set realdecimaldigits to 16.
     Set a to 10^16-2.0.
     Writeline a+0.999.
     Writeline a+0.9999.

and got:

      9999999999999999.0
      9999999999999999.0