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Save 10 bytes for backward HD6309 LZSA2 depacker

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This commit is contained in:
Doug Masten 2020-11-20 16:55:53 -06:00
parent 4d20175edd
commit 8689a42ff9
1 changed files with 18 additions and 21 deletions
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39
asm/6809/unlzsa2b-6309.s
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@ -1,4 +1,4 @@
; unlzsa2b-6309.s - H6309 backward decompressor for raw LZSA2 - 163 bytes ; unlzsa2b-6309.s - H6309 backward decompressor for raw LZSA2 - 155 bytes
; compress with lzsa -f2 -r -b <original_file> <compressed_file> ; compress with lzsa -f2 -r -b <original_file> <compressed_file>
; ;
; in: x = last byte of compressed data ; in: x = last byte of compressed data
@ -25,8 +25,7 @@
decompress_lzsa2 decompress_lzsa2
clr lz2nibct ; reset nibble available flag clr lz2nibct ; reset nibble available flag
leax 1,x leax 1,x ; adjust compressed data pointer
leay 1,y
bra lz2token bra lz2token
lz2nibct fcb 0 ; nibble ready flag lz2nibct fcb 0 ; nibble ready flag
@ -35,7 +34,7 @@ lz2replg lslb ; push token's Y flag bit into carry
bcs lz2rep16 ; if token's Y bit is set, rep or 16 bit offset bcs lz2rep16 ; if token's Y bit is set, rep or 16 bit offset
sex ; push token's Z flag bit into reg A sex ; push token's Z flag bit into reg A
lbsr lz2nibl ; get offset nibble in B bsr lz2nibl ; get offset nibble in B
lsla ; push token's Z flag bit into carry lsla ; push token's Z flag bit into carry
rolb ; shift Z flag from carry into bit 0 of B rolb ; shift Z flag from carry into bit 0 of B
eorb #$e1 ; set bits 13-15 of offset, reverse bit 8 eorb #$e1 ; set bits 13-15 of offset, reverse bit 8
@ -48,7 +47,6 @@ lz2rep16 bmi lz2repof ; if token's Z flag bit is set, rep match
lz2lowof ldb ,-x ; load low 8 bits of offset lz2lowof ldb ,-x ; load low 8 bits of offset
lz2gotof negd ; reverse sign of offset in D lz2gotof negd ; reverse sign of offset in D
decd ; tfm below is post-decrement, not pre-decrement
std lz2moff+2 ; store match offset std lz2moff+2 ; store match offset
lz2repof ldd #$0007 ; clear MSB match length and set mask for MMM lz2repof ldd #$0007 ; clear MSB match length and set mask for MMM
@ -70,9 +68,7 @@ lz2moff leau $aaaa,y ; put backreference start address in U (dst+offset)
ldd ,--x ; load 16-bit len in D (low part in B, high in A) ldd ,--x ; load 16-bit len in D (low part in B, high in A)
lz2gotln tfr d,w ; set W with match count for TFM instruction lz2gotln tfr d,w ; set W with match count for TFM instruction
leay -1,y ; tfm is post-decrement
tfm u-,y- ; copy match bytes tfm u-,y- ; copy match bytes
leay 1,y ; fix destination for pre-decrement again
lz2token ldb ,-x ; load next token into B: XYZ|LL|MMM lz2token ldb ,-x ; load next token into B: XYZ|LL|MMM
tfr x,u ; save token address tfr x,u ; save token address
@ -92,6 +88,17 @@ lz2token ldb ,-x ; load next token into B: XYZ|LL|MMM
ldd ,--x ; load 16 bit count in D (low part in B, high in A) ldd ,--x ; load 16 bit count in D (low part in B, high in A)
bra lz2gotlt ; we now have the complete count, go copy bra lz2gotlt ; we now have the complete count, go copy
lz2nibl com lz2nibct ; nibble ready?
bpl lz2gotnb
ldb ,-x ; load two nibbles
stb lz2gotnb+1 ; store nibble for next time (low 4 bits)
lsrb ; shift 4 high bits of nibble down
lsrb
lsrb
lsrb
rts
lz2declt lsrb ; shift literals count into place lz2declt lsrb ; shift literals count into place
lsrb lsrb
lsrb lsrb
@ -99,10 +106,8 @@ lz2gotla clra ; clear A (high part of literals count)
lz2gotlt tfr d,w ; set W with literals count for TFM instruction lz2gotlt tfr d,w ; set W with literals count for TFM instruction
leax -1,x ; tfm is post-decrement leax -1,x ; tfm is post-decrement
leay -1,y
tfm x-,y- ; copy literal bytes tfm x-,y- ; copy literal bytes
leax 1,x leax 1,x
leay 1,y
lz2nolt ldb ,u ; get token again lz2nolt ldb ,u ; get token again
lslb ; push token's X flag bit into carry lslb ; push token's X flag bit into carry
@ -122,15 +127,7 @@ lz2nolt ldb ,u ; get token again
lz2offs9 deca ; set bits 9-15 of offset, reverse bit 8 lz2offs9 deca ; set bits 9-15 of offset, reverse bit 8
bra lz2lowof bra lz2lowof
lz2nibl ldb #$aa lz2done leay 1,y ; adjust pointer to first byte of decompressed data and then exit
com lz2nibct ; nibble ready? lz2gotnb ldb #$aa ; load nibble
bpl lz2gotnb andb #$0f ; only keep low 4 bits
rts
ldb ,-x ; load two nibbles
stb lz2nibl+1 ; store nibble for next time (low 4 bits)
lsrb ; shift 4 high bits of nibble down
lsrb
lsrb
lsrb
lz2gotnb andb #$0f ; only keep low 4 bits
lz2done rts