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Slight speed and space improvement to nibble processing in 6809 LZSA2 depackers

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This commit is contained in:
Doug Masten
2020-06-30 14:05:59 -05:00
parent 214e03555f
commit 31d5dc2419
2 changed files with 10 additions and 12 deletions
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9
asm/6809/unlzsa2.s
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@@ -1,4 +1,4 @@
; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 172 bytes ; unlzsa2.s - 6809 decompression routine for raw LZSA2 - 169 bytes
; compress with lzsa -f2 -r <original_file> <compressed_file> ; compress with lzsa -f2 -r <original_file> <compressed_file>
; ;
; in: x = start of compressed data ; in: x = start of compressed data
@@ -24,7 +24,7 @@
; 3. This notice may not be removed or altered from any source distribution. ; 3. This notice may not be removed or altered from any source distribution.
decompress_lzsa2 decompress_lzsa2
lsr <lz2nibct,pcr ; reset nibble available flag clr <lz2nibct,pcr ; reset nibble available flag
lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM lz2token ldb ,x+ ; load next token into B: XYZ|LL|MMM
pshs b ; save it pshs b ; save it
@@ -83,10 +83,9 @@ lz2offs9 deca ; set bits 9-15 of offset, reverse bit 8
lz2nibct fcb $00 ; nibble ready flag lz2nibct fcb $00 ; nibble ready flag
lz2nibl ldb #$aa lz2nibl ldb #$aa
lsr <lz2nibct,pcr ; nibble ready? com <lz2nibct,pcr ; toggle nibble ready flag and check
bcs lz2gotnb bpl lz2gotnb
inc <lz2nibct,pcr ; flag nibble as ready for next time
ldb ,x+ ; load two nibbles ldb ,x+ ; load two nibbles
stb <lz2nibl+1,pcr ; store nibble for next time (low 4 bits) stb <lz2nibl+1,pcr ; store nibble for next time (low 4 bits)

13
asm/6809/unlzsa2b.s
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@@ -1,4 +1,4 @@
; unlzsa2b.s - 6809 backward decompression routine for raw LZSA2 - 174 bytes ; unlzsa2b.s - 6809 backward decompression routine for raw LZSA2 - 171 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
@@ -24,7 +24,7 @@
; 3. This notice may not be removed or altered from any source distribution. ; 3. This notice may not be removed or altered from any source distribution.
decompress_lzsa2 decompress_lzsa2
lsr <lz2nibct,pcr ; reset nibble available flag clr <lz2nibct,pcr ; reset nibble available flag
leax 1,x leax 1,x
leay 1,y leay 1,y
@@ -41,7 +41,7 @@ lz2token ldb ,-x ; load next token into B: XYZ|LL|MMM
cmpb #$12 ; LITERALS_RUN_LEN_V2 + 15 ? cmpb #$12 ; LITERALS_RUN_LEN_V2 + 15 ?
bne lz2gotla ; if not, we have the full literals count, go copy bne lz2gotla ; if not, we have the full literals count, go copy
addb ,-x ; add extra literals count byte + LITERALS_RUN_LEN + 15 addb ,-x ; add extra literals count byte + LITERALS_RUN_LEN + 15
bcc lz2gotla ; if no overflow, we got the complete count, copy bcc lz2gotla ; if no overflow, we got the complete count, copy
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)
@@ -77,16 +77,15 @@ lz2nolt ldb ,s ; get token again, don't pop it from the stack
sex ; set bits 8-15 of offset to $FF sex ; set bits 8-15 of offset to $FF
bra lz2gotof bra lz2gotof
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
lz2nibct fcb $00 ; nibble ready flag lz2nibct fcb $00 ; nibble ready flag
lz2nibl ldb #$aa lz2nibl ldb #$aa
lsr <lz2nibct,pcr ; nibble ready? com <lz2nibct,pcr ; toggle nibble ready flag and check
bcs lz2gotnb bpl lz2gotnb
inc <lz2nibct,pcr ; flag nibble as ready for next time
ldb ,-x ; load two nibbles ldb ,-x ; load two nibbles
stb <lz2nibl+1,pcr ; store nibble for next time (low 4 bits) stb <lz2nibl+1,pcr ; store nibble for next time (low 4 bits)