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Restructure code to eliminate one BRA instruction from loop in 6809 LZSA1 depacker

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This commit is contained in:
Doug Masten 2020-06-26 23:38:29 -05:00
parent 0307d228a0
commit 27562f4761
1 changed files with 39 additions and 39 deletions
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78
asm/6809/unlzsa1b.s
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@ -26,6 +26,43 @@
decompress_lzsa1
leax 1,x
leay 1,y
bra lz1token
lz1bigof ldd ,--x ; O set: load long 16 bit (negative, signed) offset
lz1gotof nega ; reverse sign of offset in D
negb
sbca #0
leau d,y ; put backreference start address in U (dst+offset)
puls b ; restore token
clra ; clear A (high part of match length)
andb #$0F ; isolate MMMM (embedded match length)
addb #$03 ; add MIN_MATCH_SIZE
cmpb #$12 ; MATCH_RUN_LEN?
bne lz1gotln ; no, we have the full match length, go copy
addb ,-x ; add extra match length byte + MIN_MATCH_SIZE + MATCH_RUN_LEN
bcc lz1gotln ; if no overflow, we have the full length
bne lz1midln
ldd ,--x ; load 16-bit len in D (low part in B, high in A)
bne lz1gotln ; check if we hit EOD (16-bit length = 0)
rts ; done, bail
lz1midln tfr b,a ; copy high part of len into A
ldb ,-x ; grab low 8 bits of len in B
lz1gotln pshs x ; save source compressed data pointer
tfr d,x ; copy match length to X
lz1cpymt lda ,-u ; copy matched byte
sta ,-y
leax -1,x ; decrement X
bne lz1cpymt ; loop until all matched bytes are copied
puls x ; restore source compressed data pointer
lz1token ldb ,-x ; load next token into B: O|LLL|MMMM
pshs b ; save it
@ -52,11 +89,11 @@ lz1declt lsrb ; shift literals count into place
lsrb
lsrb
lsrb
lz1gotlt tfr x,u
tfr d,x ; transfer 16-bit count into X
lz1cpylt lda ,-u ; copy literal byte
sta ,-y
sta ,-y
leax -1,x ; decrement X and update Z flag
bne lz1cpylt ; loop until all literal bytes are copied
tfr u,x
@ -67,40 +104,3 @@ lz1nolt ldb ,s ; get token again, don't pop it from the stack
ldb ,-x ; O clear: load 8 bit (negative, signed) offset
lda #$ff ; set high 8 bits
bra lz1gotof
lz1bigof ldd ,--x ; O set: load long 16 bit (negative, signed) offset
lz1gotof nega ; reverse sign of offset in D
negb
sbca #0
leau d,y ; put backreference start address in U (dst+offset)
puls b ; restore token
clra ; clear A (high part of match length)
andb #$0F ; isolate MMMM (embedded match length)
addb #$03 ; add MIN_MATCH_SIZE
cmpb #$12 ; MATCH_RUN_LEN?
bne lz1gotln ; no, we have the full match length, go copy
addb ,-x ; add extra match length byte + MIN_MATCH_SIZE + MATCH_RUN_LEN
bcc lz1gotln ; if no overflow, we have the full length
bne lz1midln
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)
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 pshs x ; save source compressed data pointer
tfr d,x ; copy match length to X
lz1cpymt lda ,-u ; copy matched byte
sta ,-y
leax -1,x ; decrement X
bne lz1cpymt ; loop until all matched bytes are copied
puls x ; restore source compressed data pointer
bra lz1token ; go decode next token