70 lines
1.6 KiB
ArmAsm
70 lines
1.6 KiB
ArmAsm
;; Delete the current BASIC line, which is assumed to have already
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;; been found with basic_find_line.
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;; Really only consists of copying memory down.
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;; The only complication is that we have to do the copy with ROMs
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;; banked out. Oh, yes, and we have to update all the links in
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;; the following basic lines.
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basic_delete_line:
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;; jsr printf
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;; .byte "DELETING LINE AT $"
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;; .byte $f1,<basic_current_line_ptr,>basic_current_line_ptr
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;; .byte $f0,<basic_current_line_ptr,>basic_current_line_ptr
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;; .byte $0d,0
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;; Get address of next line
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ldx #<basic_current_line_ptr
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ldy #0
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jsr peek_under_roms
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sta tokenise_work3
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iny
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jsr peek_under_roms
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sta tokenise_work4
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;; Work out length of this line by looking at the pointer
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lda tokenise_work3
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sec
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sbc basic_current_line_ptr+0
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sta tokenise_work3
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lda tokenise_work4
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sbc basic_current_line_ptr+1
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sta tokenise_work4
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;; jsr printf
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;; .byte "LINE LENGTH IS $"
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;; .byte $f0,<tokenise_work4,>tokenise_work4
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;; .byte $f0,<tokenise_work3,>tokenise_work3
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;; .byte $0d,0
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lda tokenise_work4
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sbc #0
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cmp #$00
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beq +
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;; Line length is <0 or >255 bytes.
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;; Either way, things are bad, so abort.
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jmp do_MEMORY_CORRUPT_error
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*
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;; Length can now be safely assumed to be in the low
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;; byte only, i.e., stored in tokenise_work3
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lda tokenise_work3
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pha
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tax
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;; Shuffle everything down
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jsr basic_shift_mem_down_and_relink
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;; Now decrease top of BASIC mem
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pla
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sta tokenise_work3
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lda basic_end_of_text_ptr+0
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sec
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sbc tokenise_work3
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sta basic_end_of_text_ptr+0
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lda basic_end_of_text_ptr+1
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sbc #0
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sta basic_end_of_text_ptr+1
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clc
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rts
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