Another negative thing about the table driven C type functions is that
in the PROTECTED build, there will need to be two ctyle look-up tables:
One in user space and one in kernel space. So the overhead will 512,
not 256, bytes in that configuration.
Also, a minor correction:
The table look-up version would be something like
# define isdigit(c) ( (table(c) & __DIGIT_MASK) != 0)
Given c in a register that would boil down to something like:
* get the address of the table
* offset by (c)
* Fetch table entry from FLASH (big performance hit)
* AND with __DIGIT_MASK
* compare with zero
