75 lines
1.5 KiB
ArmAsm
75 lines
1.5 KiB
ArmAsm
;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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.proc line; user-procedure :clobbers (A X Y) :clobbers-arguments 4
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.include "line.inc"
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;; Fix line that is too long
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LDA Y_pos
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CMP #$C8 ;;y_max = $C8
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BCC do_not_fix_y_pos
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LDA #$C8
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STA Y_pos
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do_not_fix_y_pos:
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LDA Y_end
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CMP #$C8 ;;y_max = $C8
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BCC do_not_fix_y_end
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LDA #$C8
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STA Y_end
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do_not_fix_y_end:
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;;dx
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SEC
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LDA X_end
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SBC X_pos
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BCS dx_no_underflow;; X_end >= X_pos
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EOR #$ff ; Fix bit underflow
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STA dx
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;; line_* expect X_pos < X_end and now its not the case.
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;; Lets move them around
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LDX X_pos
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LDY X_end
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STX X_end
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STY X_pos
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LDX Y_pos
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LDY Y_end
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STX Y_end
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STY Y_pos
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dx_no_underflow:
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STA dx
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SEC
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LDA Y_pos
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SBC Y_end
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STA dy
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BCC down ;normal Y_pos < Y_end
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up:; Y_pos > Y_end
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STA dy
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CMP dx
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BCC shallow; dy < dx
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steep:
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jsr line_up_inv
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RTS
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shallow: ;dy =< dx
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lda dx
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jsr line_up
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RTS
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down:
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EOR #$ff ; Fix bit underflow
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STA dy
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CMP dx
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BCC shallow_; dy < dx
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steep_:
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jsr line_down_inv
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RTS
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shallow_: ;dy < dx
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jsr line_down
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RTS
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.include "line_down.s"
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.include "line_down_inv.s"
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.include "line_up.s"
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.include "line_up_inv.s"
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.endproc
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