WP 34S and 31S bugs and fixes

[Nigel (UK)]

Thank you Bit! There's (surely) something here to satisfy everyone. I have not explored every possible combination of options but so far I have found no bugs. Those of you who do not compile the code yourself might nevertheless like to take a look at the file trunk/features.h to see the fine-grained control that Bit's code allows.

Here are the options that I would choose for the default build:

• Both positive and negative exponent entry to be type 1, so that exponents outside the range of the limits are allowed so long as the complete number is within range. So 0.1 EEX 385 is fine.
• Don't allow sign changing if it results in an illegal exponent (SP_EXP_ENTRY_CHS type 1). This removes the anomaly of 1 EEX 3 8 4 +/- being legal while 1 EEX +/- 384 is forbidden; both are now forbidden.
• Show a warning on illegal exponent entry rather than silently blocking the entry of illegal digits. This error should be clear and so should take up two lines.
  

Going beyond these, it would be nice to allow any exponent if the mantissa is zero - i.e., 0 EEX 9 9 9 should not throw a TOO BIG error. This isn't currently an option in the code so far as I can see. I don't feel strongly about this, but the errors are odd.

These choices are not fully consistent with the existing documentation but I feel that any small discrepancies are a price worth paying for the consistency in number entry that Bit's code allows.

Nigel (UK)

[Edited for clarity and correctness. I had not fully understood the rather large range of options available at the time of my first post. Edited again for the same reason. I hope I've understood it properly this time!]