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compression.asm
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compression.asm
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;Command set 1 jump table
copy_or_return_1_entry:
NOP ;$BB8000 \ Decompression command entry
JMP copy_or_return_1 ;$BB8001 /
stream_byte_1_entry:
NOP ;$BB8004 \ Decompression command entry
JMP stream_byte_1 ;$BB8005 /
stream_word_1_entry:
NOP ;$BB8008 \ Decompression command entry
JMP stream_word_1 ;$BB8009 /
stream_byte_fill_1_entry:
NOP ;$BB800C \ Decompression command entry
JMP stream_byte_fill_1 ;$BB800D /
direct_byte_1_fill_1_entry:
NOP ;$BB8010 \ Decompression command entry
JMP direct_byte_1_fill_1 ;$BB8011 /
direct_byte_2_fill_1_entry:
NOP ;$BB8014 \ Decompression command entry
JMP direct_byte_2_fill_1 ;$BB8015 /
direct_word_put_1_entry:
NOP ;$BB8018 \ Decompression command entry
JMP direct_word_put_1 ;$BB8019 /
direct_byte_1_put_1_entry:
NOP ;$BB801C \ Decompression command entry
JMP direct_byte_1_put_1 ;$BB801D /
direct_byte_2_put_1_entry:
NOP ;$BB8020 \ Decompression command entry
JMP direct_byte_2_put_1 ;$BB8021 /
back_copy_word_1_entry:
NOP ;$BB8024 \ Decompression command entry
JMP back_copy_word_1 ;$BB8025 /
back_copy_1_entry:
NOP ;$BB8028 \ Decompression command entry
JMP back_copy_1 ;$BB8029 /
back_copy_far_1_entry:
NOP ;$BB802C \ Decompression command entry
JMP back_copy_far_1 ;$BB802D /
back_copy_arbitrary_1_entry:
NOP ;$BB8030 \ Decompression command entry
JMP back_copy_arbitrary_1 ;$BB8031 /
duplicate_byte_1_entry:
NOP ;$BB8034 \ Decompression command entry
JMP duplicate_byte_1 ;$BB8035 /
duplicate_word_1_entry:
NOP ;$BB8038 \ Decompression command entry
JMP duplicate_word_1 ;$BB8039 /
copy_future_word_1_entry:
NOP ;$BB803C \ Decompression command entry
JMP copy_future_word_1 ;$BB803D /
;Command set 2 jump table
copy_or_return_2_entry:
JMP copy_or_return_2 ;$BB8040 > Decompression command entry
stream_byte_2_entry:
NOP ;$BB8043 \ Decompression command entry
JMP stream_byte_2 ;$BB8044 /
stream_word_2_entry:
NOP ;$BB8047 \ Decompression command entry
JMP stream_word_2 ;$BB8048 /
stream_byte_fill_2_entry:
NOP ;$BB804B \ Decompression command entry
JMP stream_byte_fill_2 ;$BB804C /
direct_byte_1_fill_2_entry:
NOP ;$BB804F \ Decompression command entry
JMP direct_byte_1_fill_2 ;$BB8050 /
direct_byte_2_fill_2_entry:
NOP ;$BB8053 \ Decompression command entry
JMP direct_byte_2_fill_2 ;$BB8054 /
direct_word_put_2_entry:
NOP ;$BB8057 \ Decompression command entry
JMP direct_word_put_2 ;$BB8058 /
direct_byte_1_put_2_entry:
NOP ;$BB805B \ Decompression command entry
JMP direct_byte_1_put_2 ;$BB805C /
direct_byte_2_put_2_entry:
NOP ;$BB805F \ Decompression command entry
JMP direct_byte_2_put_2 ;$BB8060 /
back_copy_word_2_entry:
NOP ;$BB8063 \ Decompression command entry
JMP back_copy_word_2 ;$BB8064 /
back_copy_2_entry:
NOP ;$BB8067 \ Decompression command entry
JMP back_copy_2 ;$BB8068 /
back_copy_far_2_entry:
NOP ;$BB806B \ Decompression command entry
JMP back_copy_far_2 ;$BB806C /
back_copy_arbitrary_2_entry:
NOP ;$BB806F \ Decompression command entry
JMP back_copy_arbitrary_2 ;$BB8070 /
duplicate_byte_2_entry:
NOP ;$BB8073 \ Decompression command entry
JMP duplicate_byte_2 ;$BB8074 /
duplicate_word_2_entry:
NOP ;$BB8077 \ Decompression command entry
JMP duplicate_word_2 ;$BB8078 /
copy_future_word_2_entry:
NOP ;$BB807B \ Decompression command entry
JMP copy_future_word_2 ;$BB807C /
;$38 -- destination
;$34 -- source
;$32 -- run dma after upload (always #$FFFF so never)
;The follow two tables map to the opposite intended nibbles.
;$42 -- index >> 4 (look up table pointer, set low byte and read for value)
; This table allow direct indexing of low nibbles
;$46 -- (index & 0x0F) << 4 (look up table pointer, set low byte and read for value)
; This table allow direct indexing of high nibbles
;$4A -- command set starting at $BB8040
;$4E -- command set starting at $BB8000
;These are the 6 header bytes of compressed data
;$52 -- fill byte 1
;$53 -- fill byte 2
;$56 -- direct byte 1
;$57 -- direct byte 2
;$54 -- direct word
;Misc addresses
;$3C -- operand 1 (usually count)
;$3E -- operand 2 (usually offset)
;Extra notes
;All commands are return addresses - 1 so RTS can be used
decompress_data: ;
STA $38 ;$BB8D91 \ Set decompression parameters
LDA #$007F ;$BB8D93 |
STA $3A ;$BB8D96 | Bank 7F + address from A
STX $34 ;$BB8D98 | Source from X
STY $36 ;$BB8D9A |
BRA start_decompression ;$BB8D9C /
;
decompress_data_default: ; \
TXA ;$BB8D9E |\ Set decompression parameters
TYX ;$BB8D9F | |
STA $34 ;$BB8DA0 | |
STX $36 ;$BB8DA2 | |
LDA #$0000 ;$BB8DA4 | | Default destination $7F0000
STA $38 ;$BB8DA7 | |
LDA #$007F ;$BB8DA9 | |
STA $3A ;$BB8DAC |/
start_decompression: ; |
LDA #$FFFF ;$BB8DAE |\ Disble auto DMA of data
STA $32 ;$BB8DB1 |/
PHB ;$BB8DB3 |\ Preserve call bank/Y
PHY ;$BB8DB4 |/
LDA #$2100 ;$BB8DB5 |\ Setup pointers to nibble look up tables
STA $46 ;$BB8DB8 | |
LDA #$007E ;$BB8DBA | |
STA $48 ;$BB8DBD | |
STA $44 ;$BB8DBF | |
LDA #$2000 ;$BB8DC1 | |
STA $42 ;$BB8DC4 |/
JSL build_decompression_lookup ;$BB8DC6 | Generate nibble offset table at RAM $7E2000
LDX $38 ;$BB8DCA | Load the decompression index
LDY #$0001 ;$BB8DCC | Load the compression index
LDA #$8001 ;$BB8DCF |\ Load default decompression function A 8001
STA $4E ;$BB8DD2 |/ The high byte will never change.
LDA #$8040 ;$BB8DD4 |\ Load default decompression function B 8040
STA $4A ;$BB8DD7 |/
SEP #$20 ;$BB8DD9 |
LDA $3A ;$BB8DDB |\ Set the data bank to the destination bank
PHA ;$BB8DDD | |
PLB ;$BB8DDE |/
LDA [$34],y ;$BB8DDF |\ Read fill byte 1
STA $52 ;$BB8DE1 | |
INY ;$BB8DE3 |/
LDA [$34],y ;$BB8DE4 |\ Read fill byte 2
STA $53 ;$BB8DE6 | |
INY ;$BB8DE8 |/
LDA [$34],y ;$BB8DE9 |\ Read direct byte 1
STA $56 ;$BB8DEB | |
INY ;$BB8DED |/
LDA [$34],y ;$BB8DEE |\ Read direct byte 2
STA $57 ;$BB8DF0 | |
INY ;$BB8DF2 |/
REP #$20 ;$BB8DF3 |\ Read direct word
LDA [$34],y ;$BB8DF5 | |
STA $54 ;$BB8DF7 |/
LDY #$0027 ;$BB8DF9 | Skip to compressed byte #$27
STZ $3C ;$BB8DFC |\ Clear generic operand 1
STZ $3E ;$BB8DFE |/ Clean generic operand 2
SEP #$20 ;$BB8E00 | Return to 8 bit
execute_command_set_1: ; |
LDA [$34],y ;$BB8E02 |\ Read the first command byte
INY ;$BB8E04 | |
STA $46 ;$BB8E05 |/
AND #$F0 ;$BB8E07 |\ Command = (byte & 0xF0) >> 2
LSR A ;$BB8E09 | | Range $00-$3C
LSR A ;$BB8E0A | |
STA $4E ;$BB8E0B |/
PEI ($4E) ;$BB8E0D | Push command address onto the stack
RTS ;$BB8E0F / Return to execute command
;
execute_command_set_2_wide: ;
LDA $46 ;$BB8E10 \ Read next command byte
AND #$0F ;$BB8E12 |\ Command = (byte & 0xF0) >> 2
ASL A ;$BB8E14 | | Range $3F-$7B
ASL A ;$BB8E15 | |
ADC #$3F ;$BB8E16 |/
STA $4A ;$BB8E18 |
PEI ($4A) ;$BB8E1A | Push command address onto the stack
RTS ;$BB8E1C / Return to execute command
;
execute_command_set_2: ;
LDA $42 ;$BB8E1D \ Read next command byte
AND #$0F ;$BB8E1F |\ Command = (byte & 0xF0) >> 2
ASL A ;$BB8E21 | | Range $3F-$7B
ASL A ;$BB8E22 | |
ADC #$3F ;$BB8E23 | |
STA $4A ;$BB8E25 |/
PEI ($4A) ;$BB8E27 | Push command address onto the stack
RTS ;$BB8E29 / Return to execute command
;
copy_or_return_1: ; \
LDA $46 ;$BB8E2A |\ Read number of bytes to copy
AND #$0F ;$BB8E2C | |
BEQ finalize_decompression ;$BB8E2E |/ If zero bytes, conclude decompression
STA $3C ;$BB8E30 | Store number of bytes to copy
.copy_byte ; |
LDA [$34],y ;$BB8E32 |\ Direct copy of up to 16 bytes
INY ;$BB8E34 | |
STA $0000,x ;$BB8E35 | |
INX ;$BB8E38 | |
DEC $3C ;$BB8E39 | |
BNE .copy_byte ;$BB8E3B |/
JMP execute_command_set_1 ;$BB8E3D / Read new command
;
finalize_decompression: ; \
REP #$20 ;$BB8E40 |\ Restore 16 bit A, data bank and Y
PLY ;$BB8E42 | |
PLB ;$BB8E43 |/
TXA ;$BB8E44 |\ Calculate the number of decompressed bytes (stored in X)
SEC ;$BB8E45 | | X = X - destination (Where X as an operand is the destination offset)
SBC $38 ;$BB8E46 | |
TAX ;$BB8E48 |/
LDA $32 ;$BB8E49 |\ Check if DMA should run
BMI .skip_DMA ;$BB8E4B |/
LDA $58 ;$BB8E4D |\ This would be a be a DMA to VRAM
STA $2116 ;$BB8E4F | | However $32 is a constant and will always be skipped (0xFFFF)
LDA $38 ;$BB8E52 | |
STA $4302 ;$BB8E54 | |
LDA $3A ;$BB8E57 | |
STA $4304 ;$BB8E59 | |
STX $4305 ;$BB8E5C | |
LDA #$1801 ;$BB8E5F | |
STA $4300 ;$BB8E62 | |
SEP #$20 ;$BB8E65 | |
LDA #$01 ;$BB8E67 | |
STA $420B ;$BB8E69 | |
REP #$20 ;$BB8E6C |/
.skip_DMA ; |
RTL ;$BB8E6E / Done with decompression
;
copy_or_return_2: ; \
LDA [$34],y ;$BB8E6F |\ Load next operand
INY ;$BB8E71 |/
STA $42 ;$BB8E72 |\ Store in nibble lookup tables
STA $46 ;$BB8E74 |/
LDA [$42] ;$BB8E76 |\ Load number of bytes to write
BEQ finalize_decompression ;$BB8E78 | | If zero bytes, conclude decompression
STA $3C ;$BB8E7A |/ Store number of bytes to write
.copy_byte ; |
LDA [$46] ;$BB8E7C |\ operand2 = high byte
STA $3E ;$BB8E7E |/
LDA [$34],y ;$BB8E80 |\ Load next operand
INY ;$BB8E82 |/
STA $42 ;$BB8E83 |\ Store in nibble lookup tables
STA $46 ;$BB8E85 |/
LDA $3E ;$BB8E87 | Load operand2
ORA [$42] ;$BB8E89 |\ write operand2 | low nibble
STA $0000,x ;$BB8E8B |/
INX ;$BB8E8E |\ Continue until no there are no more bytes
DEC $3C ;$BB8E8F | |
BNE .copy_byte ;$BB8E91 |/
JMP execute_command_set_2_wide ;$BB8E93 / Run next command
;
stream_byte_1: ; \
LDA [$46] ;$BB8E96 |\ Load operand high nibble
STA $3E ;$BB8E98 |/
LDA [$34],y ;$BB8E9A |\ Load next operand
INY ;$BB8E9C | |
STA $42 ;$BB8E9D |/
LDA $3E ;$BB8E9F | Load operand high nibble
ORA [$42] ;$BB8EA1 |\ write high nibble | low nibble
STA $0000,x ;$BB8EA3 | |
INX ;$BB8EA6 |/
JMP execute_command_set_2 ;$BB8EA7 / Run next command
;
stream_byte_2: ; \
LDA [$34],y ;$BB8EAA |\ Copy one byte from the compression stream
INY ;$BB8EAC | |
STA $0000,x ;$BB8EAD | |
INX ;$BB8EB0 |/
JMP execute_command_set_1 ;$BB8EB1 / Run next command
;
stream_word_1: ; \
LDA [$46] ;$BB8EB4 |\ Load operand high nibble into operand2
STA $3E ;$BB8EB6 |/
LDA [$34],y ;$BB8EB8 |\ Load next operand
INY ;$BB8EBA |/
STA $42 ;$BB8EBB |\ Store in nibble lookup tables
STA $46 ;$BB8EBD |/
LDA $3E ;$BB8EBF | Load operand2
ORA [$42] ;$BB8EC1 |\ write operand2 | low nibble
STA $0000,x ;$BB8EC3 | |
INX ;$BB8EC6 |/
LDA [$46] ;$BB8EC7 |\ Load operand high nibble into operand2
STA $3E ;$BB8EC9 |/
LDA [$34],y ;$BB8ECB |\ Load next operand
INY ;$BB8ECD |/
STA $42 ;$BB8ECE | Store in low nibble lookup table
LDA $3E ;$BB8ED0 | Load operand2
ORA [$42] ;$BB8ED2 |\ write operand2 | low nibble
STA $0000,x ;$BB8ED4 | |
INX ;$BB8ED7 |/
JMP execute_command_set_2 ;$BB8ED8 / Run next command
;
stream_word_2: ; \
REP #$20 ;$BB8EDB |\ Copy one word from the compression stream
LDA [$34],y ;$BB8EDD | |
STA $0000,x ;$BB8EDF | |
INY ;$BB8EE2 | |
INY ;$BB8EE3 | |
INX ;$BB8EE4 | |
INX ;$BB8EE5 | |
SEP #$20 ;$BB8EE6 |/
JMP execute_command_set_1 ;$BB8EE8 / Run next command
;
stream_byte_fill_1: ; \
LDA $46 ;$BB8EEB |\ Load operand
AND #$0F ;$BB8EED | | Count = operand & 0x0F + 3
ADC #$03 ;$BB8EEF | |
STA $3C ;$BB8EF1 |/
LDA [$34],y ;$BB8EF3 |\ Load fill byte
INY ;$BB8EF5 |/
.fill_byte ; |
STA $0000,x ;$BB8EF6 |\ Store and repeat with fill byte.
INX ;$BB8EF9 | |
DEC $3C ;$BB8EFA | |
BNE .fill_byte ;$BB8EFC |/
JMP execute_command_set_1 ;$BB8EFE / Run next command
;
stream_byte_fill_2: ; \
LDA [$34],y ;$BB8F01 |\ Load next operand
INY ;$BB8F03 |/
STA $42 ;$BB8F04 |\ Store in nibble lookup tables
STA $46 ;$BB8F06 |/
LDA [$42] ;$BB8F08 |\ Count = low nibble + 3
ADC #$03 ;$BB8F0A | |
STA $3C ;$BB8F0C |/
LDA [$46] ;$BB8F0E |\ Operand2 = high nibble
STA $3E ;$BB8F10 |/
LDA [$34],y ;$BB8F12 |\ Load next operand
INY ;$BB8F14 | |
STA $42 ;$BB8F15 |/ Store low nibble look up
LDA $3E ;$BB8F17 |\ Load operand2
ORA [$42] ;$BB8F19 |/ fill byte = operand2 | low nibble
.fill_byte ; |
STA $0000,x ;$BB8F1B |\ Store and repeat with fill byte.
INX ;$BB8F1E | |
DEC $3C ;$BB8F1F | |
BNE .fill_byte ;$BB8F21 |/
JMP execute_command_set_2 ;$BB8F23 / Run next command
;
direct_byte_1_fill_1: ; \
LDA $46 ;$BB8F26 |\ Load operand
AND #$0F ;$BB8F28 | | Count = operand & 0x0F + 3
ADC #$03 ;$BB8F2A | |
STA $3C ;$BB8F2C |/
LDA $52 ;$BB8F2E | Load fill byte 1
.fill_byte ; |
STA $0000,x ;$BB8F30 |\ Store and repeat with fill byte.
INX ;$BB8F33 | |
DEC $3C ;$BB8F34 | |
BNE .fill_byte ;$BB8F36 |/
JMP execute_command_set_1 ;$BB8F38 / Run next command
;
direct_byte_1_fill_2: ; \
LDA [$34],y ;$BB8F3B |\ Load next operand
INY ;$BB8F3D | |
STA $42 ;$BB8F3E |/ Store in low nibble lookup
LDA [$42] ;$BB8F40 |\ Count = low nibble + 3
ADC #$03 ;$BB8F42 | |
STA $3C ;$BB8F44 |/
LDA $52 ;$BB8F46 | Load fill byte 1
.fill_byte ; |
STA $0000,x ;$BB8F48 |\ Store and repeat with fill byte.
INX ;$BB8F4B | |
DEC $3C ;$BB8F4C | |
BNE .fill_byte ;$BB8F4E |/
JMP execute_command_set_2 ;$BB8F50 / Run next command
;
direct_byte_2_fill_1: ; \
LDA $46 ;$BB8F53 |\ Load operand
AND #$0F ;$BB8F55 | | Count = (operand & 0x0F) + 3
ADC #$03 ;$BB8F57 | |
STA $3C ;$BB8F59 |/
LDA $53 ;$BB8F5B | Load fill byte 2
.fill_byte ; |
STA $0000,x ;$BB8F5D |\ Store and repeat with fill byte.
INX ;$BB8F60 | |
DEC $3C ;$BB8F61 | |
BNE .fill_byte ;$BB8F63 |/
JMP execute_command_set_1 ;$BB8F65 / Run next command
;
direct_byte_2_fill_2: ; \
LDA [$34],y ;$BB8F68 |\ Load next operand
INY ;$BB8F6A | |
STA $42 ;$BB8F6B |/ Store in low nibble lookup
LDA [$42] ;$BB8F6D |\ Count = low nibble + 3
ADC #$03 ;$BB8F6F | |
STA $3C ;$BB8F71 |/
LDA $53 ;$BB8F73 | Load fill byte 2
.fill_byte ; |
STA $0000,x ;$BB8F75 |\ Store and repeat with fill byte.
INX ;$BB8F78 | |
DEC $3C ;$BB8F79 | |
BNE .fill_byte ;$BB8F7B |/
JMP execute_command_set_2 ;$BB8F7D / Run next command
;
direct_word_put_1: ; \
REP #$20 ;$BB8F80 |\ Store direct word
LDA $54 ;$BB8F82 | |
STA $0000,x ;$BB8F84 | |
INX ;$BB8F87 | |
INX ;$BB8F88 | |
SEP #$20 ;$BB8F89 |/
JMP execute_command_set_2_wide ;$BB8F8B / Run next command
;
direct_word_put_2: ; \
REP #$20 ;$BB8F8E |\ Store direct word
LDA $54 ;$BB8F90 | |
STA $0000,x ;$BB8F92 | |
INX ;$BB8F95 | |
INX ;$BB8F96 | |
SEP #$20 ;$BB8F97 |/
JMP execute_command_set_1 ;$BB8F99 / Run next command
;
direct_byte_1_put_1: ; \
LDA $56 ;$BB8F9C |\ Store direct byte 1
STA $0000,x ;$BB8F9E | |
INX ;$BB8FA1 |/
JMP execute_command_set_2_wide ;$BB8FA2 / Run next command
;
direct_byte_1_put_2: ; \
LDA $56 ;$BB8FA5 |\ Store direct byte 1
STA $0000,x ;$BB8FA7 | |
INX ;$BB8FAA |/
JMP execute_command_set_1 ;$BB8FAB / Run next command
;
direct_byte_2_put_1: ; \
LDA $57 ;$BB8FAE |\ Store direct byte 2
STA $0000,x ;$BB8FB0 | |
INX ;$BB8FB3 |/
JMP execute_command_set_2_wide ;$BB8FB4 / Run next command
;
direct_byte_2_put_2: ; \
LDA $57 ;$BB8FB7 |\ Store direct byte 2
STA $0000,x ;$BB8FB9 | |
INX ;$BB8FBC |/
JMP execute_command_set_1 ;$BB8FBD / Run next command
;
back_copy_word_1: ;
PHY ;$BB8FC0 \ Preserve compression index
LDA $46 ;$BB8FC1 | Load operand
AND #$0F ;$BB8FC3 |\ Offset = (operand & 0x0F) + 2
ADC #$02 ;$BB8FC5 | |
STA $3E ;$BB8FC7 |/
REP #$20 ;$BB8FC9 |\ Prepare to copy (1 word) from a previous point in decompressed data
TXA ;$BB8FCB | | The new offset is stored in Y
SEC ;$BB8FCC | | Y = X - offset
SBC $3E ;$BB8FCD | |
TAY ;$BB8FCF |/
LDA $0000,y ;$BB8FD0 |\ Copy from previous data
STA $0000,x ;$BB8FD3 | |
INX ;$BB8FD6 | |
INX ;$BB8FD7 |/
SEP #$20 ;$BB8FD8 | Return to 8 bit A
PLY ;$BB8FDA | Restore compression index
JMP execute_command_set_1 ;$BB8FDB / Run next command
;
back_copy_word_2: ; \
LDA [$34],y ;$BB8FDE |\ Load next operand
INY ;$BB8FE0 | |
STA $42 ;$BB8FE1 |/
LDA [$42] ;$BB8FE3 |\ Offset = low nibble + 2
ADC #$02 ;$BB8FE5 | |
STA $3E ;$BB8FE7 |/
PHY ;$BB8FE9 | Preserve compression index
REP #$20 ;$BB8FEA |\ Prepare to copy (1 word) from a previous point in decompressed data
TXA ;$BB8FEC | | The new offset is stored in Y
SEC ;$BB8FED | | Y = X - offset
SBC $3E ;$BB8FEE | |
TAY ;$BB8FF0 |/
LDA $0000,y ;$BB8FF1 |\ Copy from previous data
STA $0000,x ;$BB8FF4 | |
INX ;$BB8FF7 | |
INX ;$BB8FF8 |/
SEP #$20 ;$BB8FF9 | Return to 8 bit A
PLY ;$BB8FFB | Restore compression index
JMP execute_command_set_2 ;$BB8FFC / Run next command
;
back_copy_1: ;
LDA $46 ;$BB8FFF \ Load next operand
AND #$0F ;$BB9001 |\ Count = (operand & 0x0F) + 3
ADC #$03 ;$BB9003 | |
STA $3C ;$BB9005 |/
LDA [$34],y ;$BB9007 |\ Load next operand
STA $3E ;$BB9009 | |
INY ;$BB900B |/
PHY ;$BB900C | Preserve compression index
REP #$20 ;$BB900D |\ Prepare to copy from a previous point in decompressed data
TXA ;$BB900F | | The new offset is stored in Y
SEC ;$BB9010 | | Y = X - count - offset
SBC $3C ;$BB9011 | |
SEC ;$BB9013 | |
SBC $3E ;$BB9014 | |
TAY ;$BB9016 |/
SEP #$20 ;$BB9017 | Back to 8 bit A
.byte_copy ; |
LDA $0000,y ;$BB9019 |\ Copy from previous data
INY ;$BB901C | |
STA $0000,x ;$BB901D | |
INX ;$BB9020 |/
DEC $3C ;$BB9021 |\ Copy count number of bytes
BNE .byte_copy ;$BB9023 |/
PLY ;$BB9025 | Restore compression index
JMP execute_command_set_1 ;$BB9026 / Run next command
;
back_copy_2: ; \
LDA [$34],y ;$BB9029 |\ Load next operand
INY ;$BB902B |/
STA $42 ;$BB902C |\ Store in nibble look up tables
STA $46 ;$BB902E |/
LDA [$42] ;$BB9030 |\ Count = low nibble + 3
ADC #$03 ;$BB9032 | |
STA $3C ;$BB9034 |/
LDA [$46] ;$BB9036 |\ Store high nibble in offset
STA $3E ;$BB9038 |/
LDA [$34],y ;$BB903A |\ Load next operand and store in the low nibble lookup
INY ;$BB903C | |
STA $42 ;$BB903D |/
LDA [$42] ;$BB903F |\ offset = low nibble | offset
ORA $3E ;$BB9041 | |
STA $3E ;$BB9043 |/
PHY ;$BB9045 | Preserve compression index
REP #$20 ;$BB9046 |\ Prepare to copy from a previous point in decompressed data
TXA ;$BB9048 | | The new offset is stored in Y
SEC ;$BB9049 | | Y = X - count - offset
SBC $3C ;$BB904A | |
SEC ;$BB904C | |
SBC $3E ;$BB904D | |
TAY ;$BB904F |/
SEP #$20 ;$BB9050 | Back to 8 bit A
.byte_copy ; |
LDA $0000,y ;$BB9052 |\ Copy from previous data
INY ;$BB9055 | |
STA $0000,x ;$BB9056 | |
INX ;$BB9059 |/
DEC $3C ;$BB905A |\ Copy count number of bytes
BNE .byte_copy ;$BB905C |/
PLY ;$BB905E | Restore compression index
JMP execute_command_set_2 ;$BB905F / Run next command
;
back_copy_far_1: ;
LDA $46 ;$BB9062 \ Load next operand
AND #$0F ;$BB9064 |\ Count = (operand & 0x0F) + 3
ADC #$03 ;$BB9066 | |
STA $3C ;$BB9068 |/
LDA [$34],y ;$BB906A |\ Load next operand
INY ;$BB906C | |
XBA ;$BB906D |/ Store as high byte for the full operand
LDA [$34],y ;$BB906E |\ Load next operand store in high byte look up
INY ;$BB9070 | |
STA $46 ;$BB9071 |/
REP #$20 ;$BB9073 | Switch to 16 bit A
LSR A ;$BB9075 |\ Offset = (operand >> 4) + 0x0103
LSR A ;$BB9076 | |
LSR A ;$BB9077 | |
LSR A ;$BB9078 | |
CLC ;$BB9079 | |
ADC #$0103 ;$BB907A | |
STA $40 ;$BB907D |/
PHY ;$BB907F | Preserve compression index
TXA ;$BB9080 |\ Prepare to copy from a previous point in decompressed data
SEC ;$BB9081 | | Y = X - offset
SBC $40 ;$BB9082 | |
TAY ;$BB9084 |/
SEP #$20 ;$BB9085 | Back to 8 bit A
.byte_copy ; |
LDA $0000,y ;$BB9087 |\ Copy from previous data
INY ;$BB908A | |
STA $0000,x ;$BB908B | |
INX ;$BB908E |/
DEC $3C ;$BB908F |\ Copy count number of bytes
BNE .byte_copy ;$BB9091 |/
PLY ;$BB9093 | Restore compression index
JMP execute_command_set_2_wide ;$BB9094 / Run next command
;
back_copy_far_2: ; \
LDA [$34],y ;$BB9097 |\ Load next operand
INY ;$BB9099 | |
STA $42 ;$BB909A |/ Store in low nibble look up table
LDA [$42] ;$BB909C |\ Count = low nibble + 3
ADC #$03 ;$BB909E | |
STA $3C ;$BB90A0 |/
LDA $42 ;$BB90A2 |\ Copy the low nibble to the operand high byte
AND #$0F ;$BB90A4 | |
XBA ;$BB90A6 |/
LDA [$34],y ;$BB90A7 |\ Load the operand low byte
INY ;$BB90A9 |/
REP #$20 ;$BB90AA |\ Offset = operand + 0x0103
ADC #$0103 ;$BB90AC | |
STA $40 ;$BB90AF |/
PHY ;$BB90B1 | Preserve compression index
TXA ;$BB90B2 |\ Prepare to copy from a previous point in decompressed data
SEC ;$BB90B3 | | Y = X - offset
SBC $40 ;$BB90B4 | |
TAY ;$BB90B6 |/
SEP #$20 ;$BB90B7 | Back to 8 bit A
.byte_copy ; |
LDA $0000,y ;$BB90B9 |\ Copy from previous data
INY ;$BB90BC | |
STA $0000,x ;$BB90BD | |
INX ;$BB90C0 |/
DEC $3C ;$BB90C1 |\ Copy count number of bytes
BNE .byte_copy ;$BB90C3 |/
PLY ;$BB90C5 | Restore compression index
JMP execute_command_set_1 ;$BB90C6 / Run next command
;
back_copy_arbitrary_1: ;
LDA $46 ;$BB90C9 \ Load next operand
AND #$0F ;$BB90CB |\ Count = (operand & 0x0F) + 3
ADC #$03 ;$BB90CD | |
STA $3C ;$BB90CF |/
REP #$20 ;$BB90D1 |\ Read a big endian word for the offset
LDA [$34],y ;$BB90D3 | |
XBA ;$BB90D5 | |
STA $40 ;$BB90D6 |/
INY ;$BB90D8 |\ Increment the compression index
INY ;$BB90D9 |/
PHY ;$BB90DA | Preserve compression index
TXA ;$BB90DB |\ Prepare to copy from a previous point in decompressed data
SEC ;$BB90DC | | Y = X - offset
SBC $40 ;$BB90DD | |
TAY ;$BB90DF |/
SEP #$20 ;$BB90E0 | Back to 8 bit A
.byte_copy ; |
LDA $0000,y ;$BB90E2 |\ Copy from previous data
INY ;$BB90E5 | |
STA $0000,x ;$BB90E6 | |
INX ;$BB90E9 |/
DEC $3C ;$BB90EA |\ Copy count number of bytes
BNE .byte_copy ;$BB90EC |/
PLY ;$BB90EE | Restore compression index
JMP execute_command_set_1 ;$BB90EF / Run next command
;
back_copy_arbitrary_2: ; \
LDA [$34],y ;$BB90F2 |\ Load next operand
INY ;$BB90F4 | |
STA $42 ;$BB90F5 |/ Store in low nibble look up table
LDA [$42] ;$BB90F7 |\ Count = low nibble + 3
ADC #$03 ;$BB90F9 | |
STA $3C ;$BB90FB |/
LDA $42 ;$BB90FD |\ Copy as the operand high byte
XBA ;$BB90FF |/
LDA [$34],y ;$BB9100 |\ Load the operand low byte
INY ;$BB9102 |/
REP #$20 ;$BB9103 | Set A to 16 bit
ASL A ;$BB9105 |\ Offset = (operand << 4)
ASL A ;$BB9106 | |
ASL A ;$BB9107 | |
ASL A ;$BB9108 | |
STA $40 ;$BB9109 |/
AND #$00FF ;$BB910B | Clear the high byte of the offset
SEP #$20 ;$BB910E | Resume 8 bit A
LDA [$34],y ;$BB9110 |\ Load next operand
INY ;$BB9112 |/
PHY ;$BB9113 | Preserve compression index
STA $42 ;$BB9114 | Store the operand in the low nibble look up table
LDA [$42] ;$BB9116 |\ Load low nibble
REP #$20 ;$BB9118 | |
AND #$000F ;$BB911A |/
ORA $40 ;$BB911D |\ offset = offset | low nibble
STA $40 ;$BB911F |/
TXA ;$BB9121 |\ Prepare to copy from a previous point in decompressed data
SEC ;$BB9122 | | Y = X - offset
SBC $40 ;$BB9123 | |
TAY ;$BB9125 |/
SEP #$20 ;$BB9126 | Back to 8 bit A
.copy_byte ; |
LDA $0000,y ;$BB9128 |\ Copy from previous data
INY ;$BB912B | |
STA $0000,x ;$BB912C | |
INX ;$BB912F |/
DEC $3C ;$BB9130 |\ Copy count number of bytes
BNE .copy_byte ;$BB9132 |/
PLY ;$BB9134 | Restore compression index
JMP execute_command_set_2 ;$BB9135 / Run next command Run next command
;
duplicate_byte_1: ; \
DEX ;$BB9138 |\ Copy previous byte to the decompression stream
LDA $0000,x ;$BB9139 | |
STA $0001,x ;$BB913C | |
INX ;$BB913F | |
INX ;$BB9140 |/
JMP execute_command_set_2_wide ;$BB9141 / Run next command
;
duplicate_byte_2: ; \
DEX ;$BB9144 |\ Copy previous byte to the decompression stream
LDA $0000,x ;$BB9145 | |
STA $0001,x ;$BB9148 | |
INX ;$BB914B | |
INX ;$BB914C |/
JMP execute_command_set_1 ;$BB914D / Run next command
;
duplicate_word_1: ; \
REP #$20 ;$BB9150 |\ Copy the previous word to the decompression stream
DEX ;$BB9152 | |
DEX ;$BB9153 | | First go back two bytes
LDA $0000,x ;$BB9154 | |
STA $0002,x ;$BB9157 | |
SEP #$20 ;$BB915A | |
INX ;$BB915C | | Then jump ahead four bytes
INX ;$BB915D | |
INX ;$BB915E | |
INX ;$BB915F |/
JMP execute_command_set_2_wide ;$BB9160 / Run next command
;
duplicate_word_2: ; \
REP #$20 ;$BB9163 |\ Copy the previous word to the decompression stream
DEX ;$BB9165 | |
DEX ;$BB9166 | | First go back two bytes
LDA $0000,x ;$BB9167 | |
STA $0002,x ;$BB916A | |
SEP #$20 ;$BB916D | |
INX ;$BB916F | | Then jump ahead four bytes
INX ;$BB9170 | |
INX ;$BB9171 | |
INX ;$BB9172 |/
JMP execute_command_set_1 ;$BB9173 / Run next command
;
copy_future_word_1: ;
PHY ;$BB9176 \ Preserve compression index
LDA $46 ;$BB9177 | Load next operand
REP #$20 ;$BB9179 | Set A to 16 bit
AND #$000F ;$BB917B |\ Y = (operand << 1) + 7
ASL A ;$BB917E | |
ADC #$0007 ;$BB917F | |
TAY ;$BB9182 |/
LDA [$34],y ;$BB9183 |\ Copy word from compression stream to the decompression stream
STA $0000,x ;$BB9185 |/
SEP #$20 ;$BB9188 |\ Return to 8 bit A and increment the decompression index
INX ;$BB918A | |
INX ;$BB918B |/
PLY ;$BB918C | Restore compression index
JMP execute_command_set_1 ;$BB918D / Run next command
;
copy_future_word_2: ; \
LDA [$34],y ;$BB9190 |\ Load next operand
INY ;$BB9192 | |
STA $46 ;$BB9193 |/ Store to high nibble look up table
REP #$20 ;$BB9195 | Set A to 16 bit
AND #$00F0 ;$BB9197 |\ Operand = operand >> 3
LSR A ;$BB919A | |
LSR A ;$BB919B | |
LSR A ;$BB919C |/
PHY ;$BB919D | Preserve compression index
ADC #$0007 ;$BB919E |\ Y = operand + 7
TAY ;$BB91A1 |/
LDA [$34],y ;$BB91A2 |\ Copy word from compression stream to the decompression stream
STA $0000,x ;$BB91A4 |/
SEP #$20 ;$BB91A7 |\ Return to 8 bit A and increment the decompression index
INX ;$BB91A9 | |
INX ;$BB91AA |/
PLY ;$BB91AB | Restore compression index
JMP execute_command_set_2_wide ;$BB91AC / Run next command
;
build_decompression_lookup: ;
LDY #$0100 ;$BB91AF \ Prepare to generate the high nibble table
TDC ;$BB91B2 |\ Zero A and X and set 8 bit A
TAX ;$BB91B3 | |
SEP #$20 ;$BB91B4 |/
.build_high_nibble ; |
STA $7E2100,x ;$BB91B6 |\ Store look up value (index & 0x0F) << 4
CLC ;$BB91BA | |
ADC #$10 ;$BB91BB | |
AND #$F0 ;$BB91BD |/
INX ;$BB91BF |\ Loop through all 256 values
DEY ;$BB91C0 | |
BNE .build_high_nibble ;$BB91C1 |/
LDY #$0100 ;$BB91C3 | Prepare to generate the low nibble table
LDX #$0000 ;$BB91C6 |
.build_low_nibble ; |
TXA ;$BB91C9 |\ Store look up value (index >> 4)
LSR A ;$BB91CA | |
LSR A ;$BB91CB | |
LSR A ;$BB91CC | |
LSR A ;$BB91CD | |
STA $7E2000,x ;$BB91CE |/
INX ;$BB91D2 |\ Loop through all 256 values
DEY ;$BB91D3 | |
BNE .build_low_nibble ;$BB91D4 |/
REP #$20 ;$BB91D6 | Return to 16 bit A
RTL ;$BB91D8 / Done