Text: TT43

       Name: TT43                                                    [Show more]
       Type: Subroutine
   Category: Text
    Summary: Print a two-letter token or recursive token 0-95
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TT27 calls TT43


 Print a two-letter token, or a recursive token where the token number is in
 0-95 (so the value passed to TT27 is in the range 160-255).


 Arguments:

   A                    One of the following:

                          * 128-159 (two-letter token)

                          * 160-255 (the argument to TT27 that refers to a
                            recursive token in the range 0-95)


.TT43

 CMP #160               ; If token >= 160, then this is a recursive token, so
 BCS TT47               ; jump to TT47 below to process it

 AND #127               ; This is a two-letter token with number 128-159. The
 ASL A                  ; set of two-letter tokens is stored in a lookup table
                        ; at QQ16, with each token taking up two bytes, so to
                        ; convert this into the token's position in the table,
                        ; we subtract 128 (or just clear bit 7) and multiply
                        ; by 2 (or shift left)

 TAY                    ; Transfer the token's position into Y so we can look
                        ; up the token using absolute indexed mode

 LDA QQ16,Y             ; Get the first letter of the token and print it
 JSR TT27

 LDA QQ16+1,Y           ; Get the second letter of the token

 CMP #'?'               ; If the second letter of the token is a question mark
 BEQ TT48               ; then this is a one-letter token, so just return from
                        ; the subroutine without printing (as TT48 contains an
                        ; RTS)

 JMP TT27               ; Print the second letter and return from the
                        ; subroutine

.TT47

 SBC #160               ; This is a recursive token in the range 160-255, so
                        ; subtract 160 from the argument to get the token
                        ; number 0-95 and fall through into ex to print it