WIP: 16C firmware hack for more memory

[brouhaha]

I've fixed a few dumb mistakes that led to wrong values from the exponential functions. As far as I've seen so far, the hacked 16C microcode now gets correct results for logarithmic functions, and exponential functions when the operand doesn't cause overflow. When the exponential overflow, instead of getting 9.999999999e99, they get an NNN with an exponent greater than 99, which is displayed improperly, e.g. 1e100 displays as 1.0e-00. I need to add overflow detection; I'm going to look at how the 41C and 11C do that. On the 16C, for consistency an exponential overflow should set flag 5 (G).

The logs and exponentials are saving x in LASTx, except if number entry has not been terminated prior to the function being invoked. In other words, the sequence "4 x<>y x<>y ln" puts 4.0 in LASTx, but "4 ln" puts an NNN from the non-terminated digit entry into LASTx. I need to study how other 16C floating point functions (arithmetic, 1/x, sqrt) deal with LASTx. It l9oks like the default LASTx handling is only suited for integer functions.

I'm gradually learning a lot more details about 16C microcode internals.