mirror of
https://github.com/lscharen/iigs-game-engine.git
synced 2024-11-21 20:30:50 +00:00
Simplify and specialize the even/odd patching
Allows the odd case to be slightly more efficient and the code is cleaned up by not having to handle both even and odd alignment cases at multiple points.
This commit is contained in:
Lucas Scharenbroich
parent
536959619f
commit
a70412211c
@ -31,9 +31,12 @@
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; sep #$20 ; 3
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; ldal l_is_jmp+3-base ; 5
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; pha ; 3 = 17 cycles
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;
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; Even if some additional branch is needed, it is likely to be a small improvement for the PEA case
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; and a significant improvement for the other cases since it avoids the chain of BIT instructions
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; Simple function that restores the saved opcode that are stashed in _applyBG0Xpos. It is
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; very important that opcodes are restored before new ones are inserted, because there is
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; very important that opcodes are restored before new ones are inserted, because there is
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; only one, fixed storage location and old values will be overwritten if operations are not
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; performed in order.
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;
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@ -229,46 +232,26 @@ _ApplyBG0XPos
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; +-----------+
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lda StartXMod164
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; Right now we have the offset of the left-edge visible byte. Move one byte earlier to figure out
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; where the exit will be patched in
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dec ; (a - 1) % 164
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bpl *+5
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lda #163
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bit #$0001
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jne :odd_case ; Specialized routines for even/odd cases
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; If the exit byte is odd, then the left edge is even-aligned and we round down and exit at at
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; that word.
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;
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; If the exit byte is even, then the left edge is odd-aligned and we exit at this word.
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bit #$0001
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beq :odd_exit
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; This is the even code path
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and #$FFFE
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tax
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lda CodeFieldEvenBRA,x
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lda CodeFieldEvenBRA-2,x
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sta :exit_bra
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lda Col2CodeOffset,x
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sta :exit_offset
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sta LastPatchOffset ; Cache as a flag for later
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bra :do_entry
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; This is the odd code path
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:odd_exit tax
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lda CodeFieldOddBRA,x
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sta :exit_bra
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lda Col2CodeOffset,x
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lda Col2CodeOffset-2,x
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sta :exit_offset
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sta LastPatchOffset ; Cache as a flag for later
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; Calculate the entry point into the code field by calculating the right edge
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:do_entry lda StartXMod164
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txa ; lda StartXMod164
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clc
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adc ScreenWidth ; move to the right edge and back up a byte
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dec ; to get the index of the first on-screen byte
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adc ScreenWidth ; move to the right edge
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cmp #164 ; Keep the value in range
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bcc *+5
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@ -284,30 +267,12 @@ _ApplyBG0XPos
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; changed depending on even/odd alignment in order to do the work with a single 16-bit
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; store instead of two 8-bit stores.
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bit #$0001
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beq :odd_entry
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and #$FFFE
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tax
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lda Col2CodeOffset-1,x ; Only use the one byte for the entry_offset
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lda Col2CodeOffset-3,x ; Only use the one byte for the entry_offset
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and #$FF00
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ora #$004C ; Merge in the JMP instruction
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sta :opcode
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stz :odd_entry_offset ; mark as an even case
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bra :prep_complete
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:odd_entry
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tax
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lda Col2CodeOffset-1,x
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and #$FF00
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ora #$00AF
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sta :opcode
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lda Col2CodeOffset-2,x
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sta :odd_entry_offset ; will the the actual location to jump to
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:prep_complete
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; Main loop that
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;
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; 1. Saves the opcodes in the code field
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@ -318,7 +283,7 @@ _ApplyBG0XPos
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tsc
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sta :stk_save
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:loop
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:even_loop
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ldx :virt_line_x2
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ldal BTableHigh,x ; Get the bank
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@ -360,28 +325,12 @@ _ApplyBG0XPos
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lda :exit_bra ; Copy this value into all of the lines
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SetConst ; All registers are preserved
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; Next, patch in the CODE_ENTRY value, which is the low byte of a JMP instruction. This is an
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; 8-bit operation and, since the PEA code is bank aligned, we use the entry_offset value directly
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;
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; Now, patch in the opcode + code entry_offset
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ldy :base_address
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lda :opcode
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SetCodeEntryOpcode ; All registers are preserved
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; If this is an odd entry, also set the odd_entry low byte and save the operand high byte
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lda :odd_entry_offset
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jeq :not_odd
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sep #$20
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SetOddCodeEntry ; All registers are preserved
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rep #$20
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SaveHighOperand :exit_address ; Only used once, so "inline" it
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:not_odd
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; Do the end of the loop -- update the virtual line counter and reduce the number
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; of lines left to render
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@ -395,7 +344,101 @@ _ApplyBG0XPos
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sbc :draw_count_x2
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sta :lines_left_x2
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jne :loop
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jne :even_loop
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lda :stk_save
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tcs
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plb
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rts
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:odd_case
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dec
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tax
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lda CodeFieldOddBRA,x
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sta :exit_bra
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lda Col2CodeOffset,x
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sta :exit_offset
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sta LastPatchOffset ; Cache as a flag for later
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txa ; StartXMod164 - 1
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clc
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adc ScreenWidth
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cmp #164 ; Keep the value in range
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bcc *+5
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sbc #164
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tax
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lda Col2CodeOffset-1,x
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and #$FF00
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ora #$00AF
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sta :opcode
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lda Col2CodeOffset-2,x
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sta :odd_entry_offset
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; Main loop
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phb ; Save the existing bank
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tsc
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sta :stk_save
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:odd_loop
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ldx :virt_line_x2
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ldal BTableHigh,x ; Get the bank
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pha
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plb
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ldal BTableLow,x ; Get the address of the first code field line
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tay ; Save it to use as the base address
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txa ; Calculate number of lines to draw on this iteration
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and #$001E
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eor #$FFFF
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sec
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adc #32
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min :lines_left_x2
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sta :draw_count_x2
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tax ; Use for the first iteration
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tya
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clc
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adc :exit_offset ; Add some offsets to get the base address in the code field line
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sta :exit_address
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sty :base_address
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; At this point y = :base_address, x = :draw_count_x2 and the accumulator is the exit_address
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SaveOpcodeAndOperand ; X = :exit_address on return
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txy ; ldy :exit_address -- starting at this address
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ldx :draw_count_x2 ; Do this many lines
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lda :exit_bra ; Copy this value into all of the lines
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SetConst ; All registers are preserved
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; Now, patch in the opcode + code entry_offset
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ldy :base_address
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lda :opcode
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SetCodeEntryOpcode ; All registers are preserved
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; The odd case need to do a bit of extra work
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sep #$20
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lda :odd_entry_offset
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SetOddCodeEntry ; All registers are preserved
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rep #$21 ; Clear the carry
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lda :virt_line_x2 ; advance to the virtual line after
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adc :draw_count_x2 ; filled in
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sta :virt_line_x2
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lda :lines_left_x2 ; subtract the number of lines we just completed
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sec
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sbc :draw_count_x2
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sta :lines_left_x2
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jne :odd_loop
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lda :stk_save
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tcs
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@ -413,18 +456,18 @@ _ApplyBG0XPos
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; The two unrolled loop elements are:
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;
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; Even:
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; lda: $0000,x ; Load from BTableLow + exit_offset
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; lda: $0000,x ; Load from X = BTableLow + exit_offset
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; sta: OPCODE_SAVE,y ; Save the two byte in another area of the line code
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; lda :exit_bra
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; lda :exit_bra[n]
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; sta $0000,x ; Replace the two bytes with a BRA instruction to exit the blitter
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; lda :opcode|:entry_offset
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; lda :opcode[n]
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; sta: CODE_ENTRY_OPCODE,y ; CODE_ENTRY_OPCODE and CODE_ENTRY are adjacent -- could make this a single 16-bit store
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;
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; Odd:
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; Same as above, plus...
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; lda :odd_entry_offset ; Get back into the code after fixing up the odd edge
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; lda :odd_entry_offset[n] ; [8-bit] Get back into the code after fixing up the odd edge
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; sta: ODD_ENTRY,y
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; lda: $0002,x ; Save the high byte in case the last instruction is PEA and we need to load the top byte
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; lda: $0001,x ; Save the high word in case the last instruction is PEA and we need to load the top byte
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; sta: OPCODE_HIGH_SAVE,y
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;
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_ApplyBG0XPosPerScanline
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@ -494,6 +537,21 @@ _ApplyBG0XPosPerScanline
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plb
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rts
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; Run through and build an array of scanline data and place it in temporary zero page space. Need a total of 48 bytes.
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:BuildScanlineData
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; First step, run though and create the tables for the copy routine
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lda StartXMod164Tbl,x
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bit #$0001
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; bne :bsd_odd
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tay
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lda CodeFieldEvenBRA-2,y ; The exit point comes after the left edge (reverse order due to stack)
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sta :exit_bra,x
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lda Col2CodeOffset-2,y
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sta :exit_offset,x
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:DoScanlineRange
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ldx :virt_line_x2
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@ -503,31 +561,36 @@ _ApplyBG0XPosPerScanline
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bit #$0001
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bne :is_odd ; Quickly switch to specialized even/odd routines
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; For even offsets, the index is x - 2
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; For odd offsets, the index is x - 1
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;
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; So, for both we can do (x - 1) & $FFFE = dec / and #$FFFE = lsr / asl + clears the carry
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; This is an even-aligned line
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dec ; Move to the previous address for entry (a - 1) % 164
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dec ; Optimization: Coule eliminate this with a double-width tbale for CodeFieldEvenBRA
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bpl *+5
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lda #162
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; dec ; Move to the previous address for entry (a - 1) % 164
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; dec ; Optimization: Coule eliminate this with a double-width tbale for CodeFieldEvenBRA
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; bpl *+5
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; lda #162
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; and #$FFFE ; Must be even by construction
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tay
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lda CodeFieldEvenBRA,y
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lda CodeFieldEvenBRA-2,y
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sta :exit_bra ; Store are exit_offset +
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lda Col2CodeOffset,y
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lda Col2CodeOffset-2,y
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sta :exit_offset
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tya
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adc ScreenWidth
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cmp #164 ; Keep the value in range
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bcc *+5
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sbc #164
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tay
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; tya
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; adc ScreenWidth
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; cmp #164 ; Keep the value in range
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; bcc *+5
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; sbc #164
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; tay
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lda Col2CodeOffset,y
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sta :entry_offset
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; lda #$004C ; set the entry_jmp opcode to JMP
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; sta :opcode
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lda Col2CodeOffset-2-1,y ; -2 for even case , -1 to load value into high byte
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and #$FF00
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; sta :entry_offset
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ora #$004C ; set the entry_jmp opcode to JMP
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sta :opcode
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; stz :odd_entry_offset ; mark as an even case
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ldal BTableLow,x ; Get the address of the code field line
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@ -900,6 +963,119 @@ x01 lda: $0000,x
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bottom
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<<<
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; SaveOpcodeAndOperand
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;
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; Save both the opcode and operand at the same time
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;
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; X = number of lines * 2, 0 to 32
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; Y = starting line * $1000
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; A = code field location * $1000
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SaveOpcodeAndOperand mac
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jmp (dispTbl,x)
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dispTbl da bottom
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da do01,do02,do03,do04
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da do05,do06,do07,do08
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da do09,do10,do11,do12
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da do13,do14,do15,do16
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do15 tax
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jmp x15
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do14 tax
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jmp x14
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do13 tax
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jmp x13
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do12 tax
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jmp x12
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do11 tax
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jmp x11
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do10 tax
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jmp x10
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do09 tax
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jmp x09
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do08 tax
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jmp x08
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do07 tax
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jmp x07
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do06 tax
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jmp x06
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do05 tax
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jmp x05
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do04 tax
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jmp x04
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do03 tax
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jmp x03
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do02 tax
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jmp x02
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do01 tax
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jmp x01
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do16 tax
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x16 lda $F000,x
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sta OPCODE_SAVE+$F000,y
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lda $F001,x
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sta OPCODE_HIGH_SAVE+$F000,y
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x15 lda $E000,x
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sta OPCODE_SAVE+$E000,y
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lda $E001,x
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sta OPCODE_HIGH_SAVE+$E000,y
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x14 lda $D000,x
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sta OPCODE_SAVE+$D000,y
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lda $D001,x
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sta OPCODE_HIGH_SAVE+$D000,y
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x13 lda $C000,x
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sta OPCODE_SAVE+$C000,y
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lda $C001,x
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sta OPCODE_HIGH_SAVE+$C000,y
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x12 lda $B000,x
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sta OPCODE_SAVE+$B000,y
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lda $B001,x
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sta OPCODE_HIGH_SAVE+$B000,y
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x11 lda $A000,x
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sta OPCODE_SAVE+$A000,y
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lda $A001,x
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sta OPCODE_HIGH_SAVE+$A000,y
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x10 lda $9000,x
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sta OPCODE_SAVE+$9000,y
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lda $9001,x
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sta OPCODE_HIGH_SAVE+$9000,y
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x09 lda $8000,x
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sta OPCODE_SAVE+$8000,y
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lda $8001,x
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sta OPCODE_HIGH_SAVE+$8000,y
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x08 lda $7000,x
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sta OPCODE_SAVE+$7000,y
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lda $7001,x
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sta OPCODE_HIGH_SAVE+$7000,y
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x07 lda $6000,x
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sta OPCODE_SAVE+$6000,y
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lda $6001,x
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sta OPCODE_HIGH_SAVE+$6000,y
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x06 lda $5000,x
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sta OPCODE_SAVE+$5000,y
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lda $5001,x
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sta OPCODE_HIGH_SAVE+$5000,y
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x05 lda $4000,x
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sta OPCODE_SAVE+$4000,y
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lda $4001,x
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sta OPCODE_HIGH_SAVE+$4000,y
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x04 lda $3000,x
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sta OPCODE_SAVE+$3000,y
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lda $3001,x
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sta OPCODE_HIGH_SAVE+$3000,y
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x03 lda $2000,x
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sta OPCODE_SAVE+$2000,y
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lda $2001,x
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sta OPCODE_HIGH_SAVE+$2000,y
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x02 lda $1000,x
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sta OPCODE_SAVE+$1000,y
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lda $1001,x
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sta OPCODE_HIGH_SAVE+$1000,y
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x01 lda: $0000,x
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sta: OPCODE_SAVE+$0000,y
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lda: $0001,x
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sta: OPCODE_HIGH_SAVE+$0000,y
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bottom
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<<<
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; RestoreOpcode
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;
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; Restore the values back to the code field.
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@ -129,6 +129,7 @@ JTableOffset ENT
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;
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; These tables are reversed to be parallel with the JTableOffset and Col2CodeOffset tables above. The
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; physical word index that each instruction is intended to be placed at is in the comment.
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bra *-3 ; wrap around
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CodeFieldEvenBRA ENT
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bra *+6 ; 81 -- need to skip over the JMP loop that passed control back
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bra *+9 ; 80
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@ -213,6 +214,7 @@ CodeFieldEvenBRA ENT
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bra *-6 ; 1
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bra *-3 ; 0
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bra *-6 ; wrap around
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CodeFieldOddBRA ENT
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bra *+9 ; 81 -- need to skip over two JMP instructions
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bra *+12 ; 80
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