chrget.dasm16

;
; This is an important subroutine that controls BASIC's execution
; cursor, located ar [RAM7A].  Optimizing this will speed up
; BASIC's execution time, so we want to make sure that this routine
; is as tight as possible, and that the macros/defines at the bottom
; are always used to handle the return values other than A.
; 
;  CHRGET: Move BASIC's execution cursor to next character, then
;  CHRGOT: Read character at execution cursor into A
;  RAM0080: ?
;     returns:
;  A contains the character or BASIC token fetched.
;  A=0 for end of line
;  C=0 for digits, C=1 for all other characters
;  Z=1 for end of statement (i.e. null or ASCII colon)
:CHRGET
:RAM0073    ADD [RAM7A], 1
:CHRGOT
:RAM0079    DAT 0x7801 ;SET A, [next word]
:TXTPTR
:RAM7A      DAT 0x0800
            SET C, 1
            SET Z, 0
            IFE A, CBM_COLON
                SET Z, 1  ; return Z=1 for end of statement
            IFG A, 0x39  ; Not a digit or space
                RTS      ; return C=1
:RAM0080    IFE A, CBM_SPACE ; Space
            JMP CHRGET  ; skip to next character
            SET C, 0
            IFL A, 0x30  ; Is a digit
:RAM008C        SET C, 1 ; C=1, is not a digit
            IFE A, 0
:RAM008Z        SET Z, 1
            RTS

; need better names for these
.DEFINE IF_NEXT_STMT     IFN Z, 0
.DEFINE IF_NOT_NEXT_STMT IFE Z, 0
.DEFINE IF_NOT_DIGIT     IFN C, 0
.DEFINE IF_IS_DIGIT      IFE C, 0