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| author | Juan J. Martinez <jjm@usebox.net> | 2021-01-09 09:01:05 +0000 |
|---|---|---|
| committer | Juan J. Martinez <jjm@usebox.net> | 2021-01-09 09:01:05 +0000 |
| commit | 9bcf1e97960c0da7322a868efdbc07e2650716fe (patch) | |
| tree | de6d32ad5b0e567991bd3eb262902c15a77074d9 /tools/apultra/asm/6809/unaplib_b.s | |
| parent | 3b31adf01305e522f7e28c1435fb47418ce43267 (diff) | |
| download | ubox-msx-lib-9bcf1e97960c0da7322a868efdbc07e2650716fe.tar.gz ubox-msx-lib-9bcf1e97960c0da7322a868efdbc07e2650716fe.zip | |
Extra libs: ap.lib
aPLib support with apultra.
Diffstat (limited to 'tools/apultra/asm/6809/unaplib_b.s')
| -rw-r--r-- | tools/apultra/asm/6809/unaplib_b.s | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/tools/apultra/asm/6809/unaplib_b.s b/tools/apultra/asm/6809/unaplib_b.s new file mode 100644 index 0000000..02f943c --- /dev/null +++ b/tools/apultra/asm/6809/unaplib_b.s @@ -0,0 +1,122 @@ +; unaplib_b.s - aPLib backward decompressor for 6809 - 154 bytes
+;
+; in: x = last byte of compressed data
+; y = last byte of decompression buffer
+; out: y = first byte of decompressed data
+;
+; Copyright (C) 2020 Emmanuel Marty
+;
+; This software is provided 'as-is', without any express or implied
+; warranty. In no event will the authors be held liable for any damages
+; arising from the use of this software.
+;
+; Permission is granted to anyone to use this software for any purpose,
+; including commercial applications, and to alter it and redistribute it
+; freely, subject to the following restrictions:
+;
+; 1. The origin of this software must not be misrepresented; you must not
+; claim that you wrote the original software. If you use this software
+; in a product, an acknowledgment in the product documentation would be
+; appreciated but is not required.
+; 2. Altered source versions must be plainly marked as such, and must not be
+; misrepresented as being the original software.
+; 3. This notice may not be removed or altered from any source distribution.
+
+apl_decompress
+ lda #$80 ; initialize empty bit queue
+ sta <apbitbuf,pcr ; plus bit to roll into carry
+ leau 1,x
+ leay 1,y
+
+apcplit ldb ,-u ; copy literal byte
+apwtlit stb ,-y
+
+ lda #$03 ; set 'follows literal' flag
+
+aptoken bsr apgetbit ; read 'literal or match' bit
+ bcc apcplit ; if 0: literal
+
+ bsr apgetbit ; read '8+n bits or other type' bit
+ bcs apother ; if 11x: other type of match
+
+ sta <aplwm+2,pcr ; store 'follows literal' flag
+
+ bsr apgamma2 ; 10: read gamma2-coded high offset bits
+aplwm subd #$0000 ; high offset bits == 2 when follows_literal == 3 ?
+ bcc apnorep ; if not, not a rep-match
+
+ bsr apgamma2 ; read repmatch length
+ bra apgotlen ; go copy large match
+
+apnorep tfr b,a ; transfer high offset bits to A
+ ldb ,-u ; read low offset byte in B
+ std <aprepof+2,pcr ; store match offset
+ tfr d,x ; transfer offset to X
+
+ bsr apgamma2 ; read match length
+
+ cmpx #$7D00 ; offset >= 32000 ?
+ bge apincby2 ; if so, increase match len by 2
+ cmpx #$0500 ; offset >= 1280 ?
+ bge apincby1 ; if so, increase match len by 1
+ cmpx #$80 ; offset < 128 ?
+ bge apgotlen ; if so, increase match len by 2
+apincby2 addd #1
+apincby1 addd #1
+apgotlen pshs u ; save source compressed data pointer
+ tfr d,x ; copy match length to X
+
+aprepof leau $aaaa,y ; put backreference start address in U (dst+offset)
+
+apcpymt lda ,-u ; copy matched byte
+ sta ,-y
+ leax -1,x ; decrement X
+ bne apcpymt ; loop until all matched bytes are copied
+
+ puls u ; restore source compressed data pointer
+
+ lda #$02 ; clear 'follows literal' flag
+ bra aptoken
+
+apdibits bsr apgetbit ; read bit
+ rolb ; push into B
+apgetbit lsl <apbitbuf,pcr ; shift bit queue, and high bit into carry
+ bne apdone ; queue not empty, bits remain
+ pshs a ; push reg A
+ lda ,-u ; read 8 new bits
+ rola ; shift bit queue, and high bit into carry
+ sta <apbitbuf,pcr ; save bit queue
+ puls a,pc ; pop reg A and return
+
+apbitbuf fcb $00 ; bit queue
+
+apshort clrb
+ bsr apdibits ; read 2 offset bits
+ rolb
+ bsr apdibits ; read 4 offset bits
+ rolb
+ beq apwtlit ; go write a zero
+
+ decb ; we load below without predecrement, adjust here
+ ldb b,y ; load backreferenced byte from dst+offset
+ bra apwtlit ; go write backreferenced byte
+
+apgamma2 ldd #$1 ; init to 1 so it gets shifted to 2 below
+apg2loop bsr apgetbit ; read data bit
+ rolb ; shift into D
+ rola
+ bsr apgetbit ; read continuation bit
+ bcs apg2loop ; loop until a zero continuation bit is read
+apdone rts
+
+apother bsr apgetbit ; read '7+1 match or short literal' bit
+ bcs apshort ; if 111: 4 bit offset for 1-byte copy
+
+ ldb ,-u ; read low bits of offset + length bit in B
+ beq apdone ; check for EOD
+ clra ; clear high bits in A
+ lsrb ; shift offset in place, shift length bit into carry
+ std <aprepof+2,pcr ; store match offset
+ ldb #$01 ; len in B will be 2*1+carry:
+ rolb ; shift length, and carry into B
+ bra apgotlen ; go copy match
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