| Routines

31255: Check whether Sam has dialled a valid telephone number

Used by the routine at 30675. Returns with the zero flag set if Sam has dialled a valid telephone number, and with the telephone identifier in A.
31255 | LD HL,27466 | Point HL at the end of the phone number and location table at 27392
31258 | LD C,15 | There are 15 entries to check
31260 | LD DE,32661 | Point DE at the last digit of the phone number dialled by Sam (stored at 32658)
31263 | LD B,4 | There are 4 digits in a phone number
31265 | LD A,(DE) | A=digit of the phone number dialled by Sam
31266 | CP (HL) | Compare it with that of a phone number in the table
31267 | DEC HL | Point HL at the previous digit of the phone number
31268 | DEC DE | Point DE at the previous digit dialled by Sam
31269 | JR NZ,31276 | Jump if there's no match
31271 | DJNZ 31265 | Jump back until all 4 digits have been compared
31273 | LD A,(HL) | A=identifier of the matching telephone
31274 | RET | Return with the zero flag set
31275 | DEC HL | Point HL at the first byte of the phone number entry (the telephone identifier)
31276 | DJNZ 31275
31278 | DEC HL | Point HL at the last digit of the previous phone number in the table
31279 | DEC C | Are there any more phone numbers to check?
31280 | JR NZ,31260 | Jump back if so
31282 | AND A | Reset the zero flag
31283 | RET |