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Restructure code to eliminate one BRA instruction in unlzsa1.s 6809 LZSA depacker

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This commit is contained in:
Doug Masten 2020-06-20 12:27:31 -05:00
parent 1dd65731c4
commit e8edc3242d
1 changed files with 41 additions and 41 deletions
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82
asm/6809/unlzsa1.s
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@ -23,7 +23,45 @@
; misrepresented as being the original software.
; 3. This notice may not be removed or altered from any source distribution.
decompress_lzsa1
decompress_lzsa1 equ lz1token
lz1bigof ldb ,x+ ; O set: load long 16 bit (negative, signed) offset
lda ,x+ ; (little endian)
lz1gotof 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 #$12 ; MATCH_RUN_LEN?
bne lz1gotln ; no, we have the full match length, go copy
addb ,x+ ; add extra match length byte + MIN_MATCH_SIZE + MATCH_RUN_LEN
bcc lz1gotln ; if no overflow, we have the full length
bne lz1midln
ldb ,x+ ; load 16-bit len in D (low part in B, high in A)
lda ,x+ ; (little endian)
bne lz1gotln ; check if we hit EOD (16-bit length = 0)
tstb
bne lz1gotln ; go copy matched bytes if not
rts ; done, bail
lz1midln tfr b,a ; copy high part of len into A
ldb ,x+ ; grab low 8 bits of len in B
lz1gotln pshs x ; save source compressed data pointer
tfr d,x ; copy match length to X
lz1cpymt lda ,u+ ; copy matched byte
sta ,y+
leax -1,x ; decrement X
bne lz1cpymt ; loop until all matched bytes are copied
puls x ; restore source compressed data pointer
lz1token ldb ,x+ ; load next token into B: O|LLL|MMMM
pshs b ; save it
@ -50,11 +88,11 @@ lz1declt lsrb ; shift literals count into place
lsrb
lsrb
lsrb
lz1gotlt tfr x,u
tfr d,x ; transfer 16-bit count into X
lz1cpylt lda ,u+ ; copy literal byte
sta ,y+
sta ,y+
leax -1,x ; decrement X and update Z flag
bne lz1cpylt ; loop until all literal bytes are copied
tfr u,x
@ -65,41 +103,3 @@ lz1nolt ldb ,s ; get token again, don't pop it from the stack
ldb ,x+ ; O clear: load 8 bit (negative, signed) offset
lda #$ff ; set high 8 bits
bra lz1gotof
lz1bigof ldb ,x+ ; O set: load long 16 bit (negative, signed) offset
lda ,x+ ; (little endian)
lz1gotof 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
ldb ,x+ ; load 16-bit len in D (low part in B, high in A)
lda ,x+ ; (little endian)
bne lz1gotln ; check if we hit EOD (16-bit length = 0)
tstb
bne lz1gotln ; go copy matched bytes if not
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