| Routines

2C8D: 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 | 2C8D | CP "A" | Test against +41, the code for 'A'.
| 2C8F | CCF | Complement the carry flag.
| 2C90 | RET NC | Return if not a valid character code.
| 2C91 | CP $5B | Test against +5B, 1 more than the code for 'Z'.
| 2C93 | RET C | Return if an upper case letter.
| 2C94 | CP "a" | Test against +61, the code for 'a'.
| 2C96 | CCF | Complement the carry flag.
| 2C97 | RET NC | Return if not a valid character code.
| 2C98 | CP $7B | Test against +7B, 1 more than the code for 'z'.
| 2C9A | RET | Finished.