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Save 8 bytes for backward HD6309 LZSA1 depacker

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This commit is contained in:
Doug Masten 2020-11-20 16:14:18 -06:00
parent c304c03978
commit 4d20175edd
1 changed files with 3 additions and 7 deletions
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10
asm/6809/unlzsa1b-6309.s
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@ -1,4 +1,4 @@
; unlzsa1-6309.s - H6309 backward decompressor for raw LZSA1 - 105 bytes
; unlzsa1-6309.s - H6309 backward decompressor for raw LZSA1 - 97 bytes
; compress with lzsa -f1 -r -b <original_file> <compressed_file>
;
; in: x = last byte of compressed data
@ -25,11 +25,10 @@
decompress_lzsa1
leax 1,x
bra lz1start
bra lz1token
lz1bigof ldd ,--x ; O set: load long 16-bit (negative, signed) offest
lz1gotof negd ; reverse sign of offset in D
decd ; tfm below is post-decrement, not pre-decrement
leau d,y ; put backreference start address in U (dst+offset)
ldd #$000f ; clear MSB match length and set mask for MMMM
@ -45,15 +44,14 @@ lz1gotof negd ; reverse sign of offset in D
ldd ,--x ; load 16-bit len in D (low part in B, high in A)
bne lz1gotln ; check if we hit EOD (16-bit length = 0)
leay 1,y ; adjust pointer to first byte of decompressed data
rts ; done, bail
lz1midln tfr b,a ; copy high part of len into A
ldb ,-x ; grab low 8 bits of len in B
lz1gotln tfr d,w ; set W with match length for TFM instruction
leay -1,y ; tfm is post-decrement
tfm u-,y- ; copy match bytes
lz1start leay 1,y ; fix destination for pre-decrement again
lz1token ldb ,-x ; load next token into B: O|LLL|MMMM
pshs b ; save it
@ -83,10 +81,8 @@ lz1declt lsrb ; shift literals count into place
lz1gotla clra ; clear A (high part of literals count)
lz1gotlt tfr d,w ; set W with literals count for TFM instruction
leax -1,x ; tfm is post-decrement
leay -1,y
tfm x-,y- ; copy literal bytes
leax 1,x
leay 1,y
lz1nolt ldb ,s ; get token again, don't pop it from the stack
bmi lz1bigof ; test O bit (small or large offset)