>I realized the calculation must be done using character strings instead of numbers. I found the code on Tek-Tips, which gives the correct result:

Looks like something I did back in the 80s (when I was trying to calculate e to 600 digits). It's OK as a method, except the speed. My method was to chop it into smaller pieces and stuff them into an array, 6 digits at a time, although with IEEE number I can probably even do multiplication with 7 without overflow. So I'd do an operation on a pair of elements of two arrays and stuff into the corresponding element of the third array, take the carry to the next element and so on. The end result was converted back into a string. Used to be reasonably fast even on a Spectrum with a 1.7MHz z80.