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Optimize handling of token's Z flag bit in 6809 LZSA2 depacker

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This commit is contained in:
Doug Masten 2020-06-26 23:52:00 -05:00
parent 28ca829924
commit b8cfbbbc7b
1 changed files with 4 additions and 6 deletions
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10
asm/6809/unlzsa2b.s
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@ -68,10 +68,9 @@ lz2nolt ldb ,s ; get token again, don't pop it from the stack
lslb ; push token's Y flag bit into carry lslb ; push token's Y flag bit into carry
bcs lz2offs9 ; if token's Y bit is set, 9 bits offset bcs lz2offs9 ; if token's Y bit is set, 9 bits offset
lslb ; push token's Z flag bit into carry sex ; push token's Z flag bit into reg A
tfr cc,a ; preserve cpu flags (to preserve carry)
bsr lz2nibl ; get offset nibble in B bsr lz2nibl ; get offset nibble in B
tfr a,cc ; restore cpu flags lsla ; retrieve token's Z flag bit and push 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 #$e1 ; set bits 5-7 of offset, reverse bit 0 eorb #$e1 ; set bits 5-7 of offset, reverse bit 0
@ -105,10 +104,9 @@ lz2done rts
lz2replg lslb ; push token's Y flag bit into carry 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
lslb ; push token's Z flag bit into carry sex ; push token's Z flag bit into reg A
tfr cc,a ; preserve cpu flags (to preserve carry)
bsr lz2nibl ; get offset nibble in B bsr lz2nibl ; get offset nibble in B
tfr a,cc ; restore cpu flags lsla ; retrieve token's Z flag bit and push 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