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t/data/zx48_base.asm  view on Meta::CPAN

;; STK-VAR
STK_VAR:
        xor a                   ; clear A
        ld b,a                  ; and B, the syntax dimension counter (256)
        bit 7,c                 ; checking syntax ?
        jr nz,SV_COUNT          ; forward to SV-COUNT if so.

; runtime evaluation.

        bit 7,(hl)              ; will be reset if a simple string.
        jr nz,SV_ARRAYS         ; forward to SV-ARRAYS otherwise

        inc a                   ; set A to 1, simple string.

;; SV-SIMPLE$
SV_SIMPLE_:
        inc hl                  ; address length low
        ld c,(hl)               ; place in C
        inc hl                  ; address length high
        ld b,(hl)               ; place in B
        inc hl                  ; address start of string
        ex de,hl                ; DE = start now.
        call STK_STO__          ; routine STK-STO-$ stacks string parameters
                                ; DE start in variables area,
                                ; BC length, A=1 simple string

; the only thing now is to consider if a slice is required.

        rst 0x18                ; GET-CHAR puts character at CH_ADD in A
        jp SV_SLICE_            ; jump forward to SV-SLICE? to test for '('

; --------------------------------------------------------

; the branch was here with string and numeric arrays in runtime.

;; SV-ARRAYS
SV_ARRAYS:
        inc hl                  ; step past
        inc hl                  ; the total length
        inc hl                  ; to address Number of dimensions.
        ld b,(hl)               ; transfer to B overwriting zero.
        bit 6,c                 ; a numeric array ?
        jr z,SV_PTR             ; forward to SV-PTR with numeric arrays

        dec b                   ; ignore the final element of a string array
                                ; the fixed string size.

        jr z,SV_SIMPLE_         ; back to SV-SIMPLE$ if result is zero as has
                                ; been created with DIM a$(10) for instance
                                ; and can be treated as a simple string.

; proceed with multi-dimensioned string arrays in runtime.

        ex de,hl                ; save pointer to dimensions in DE

        rst 0x18                ; GET-CHAR looks at the BASIC line
        cp 0x28                 ; is character '(' ?
        jr nz,REPORT_3          ; to REPORT-3 if not
                                ; 'Subscript wrong'

        ex de,hl                ; dimensions pointer to HL to synchronize
                                ; with next instruction.

; runtime numeric arrays path rejoins here.

;; SV-PTR
SV_PTR:
        ex de,hl                ; save dimension pointer in DE
        jr SV_COUNT             ; forward to SV-COUNT with true no of dims
                                ; in B. As there is no initial comma the
                                ; loop is entered at the midpoint.

; ----------------------------------------------------------
; the dimension counting loop which is entered at mid-point.

;; SV-COMMA
SV_COMMA:
        push hl                 ; save counter

        rst 0x18                ; GET-CHAR

        pop hl                  ; pop counter
        cp 0x2C                 ; is character ',' ?
        jr z,SV_LOOP            ; forward to SV-LOOP if so

; in runtime the variable definition indicates a comma should appear here

        bit 7,c                 ; checking syntax ?
        jr z,REPORT_3           ; forward to REPORT-3 if not
                                ; 'Subscript error'

; proceed if checking syntax of an array?

        bit 6,c                 ; array of strings
        jr nz,SV_CLOSE          ; forward to SV-CLOSE if so

; an array of numbers.

        cp 0x29                 ; is character ')' ?
        jr nz,SV_RPT_C          ; forward to SV-RPT-C if not
                                ; 'Nonsense in BASIC'

        rst 0x20                ; NEXT-CHAR moves CH-ADD past the statement
        ret                     ; return ->

; ---

; the branch was here with an array of strings.

;; SV-CLOSE
SV_CLOSE:
        cp 0x29                 ; as above ')' could follow the expression
        jr z,SV_DIM             ; forward to SV-DIM if so

        cp 0xCC                 ; is it 'TO' ?
        jr nz,SV_RPT_C          ; to SV-RPT-C with anything else
                                ; 'Nonsense in BASIC'

; now backtrack CH_ADD to set up for slicing routine.
; Note. in a BASIC line we can safely backtrack to a colour parameter.