| Routines

11405: THE 'ALPHA' SUBROUTINE

Used by the routines at DEF_FN, INPUT, S_FN_SBRN, LOOK_VARS and usr. The routine at ALPHANUM continues here. This subroutine returns with the carry flag set if the present value of the A register denotes a valid letter of the alphabet.
Input
A | Character code
Output
F | Carry flag set if the character is a letter (A-Z, a-z)
ALPHA | 11405 | CP "A" | Test against 65, the code for 'A'.
| 11407 | CCF | Complement the carry flag.
| 11408 | RET NC | Return if not a valid character code.
| 11409 | CP 91 | Test against 91, 1 more than the code for 'Z'.
| 11411 | RET C | Return if an upper case letter.
| 11412 | CP "a" | Test against 97, the code for 'a'.
| 11414 | CCF | Complement the carry flag.
| 11415 | RET NC | Return if not a valid character code.
| 11416 | CP 123 | Test against 123, 1 more than the code for 'z'.
| 11418 | RET | Finished.