From c67a4ea718ea6b3859a6986c543d58945a193995 Mon Sep 17 00:00:00 2001
From: Martin Haye <martin.haye@ucop.edu>
Date: Mon, 2 Jan 2017 11:14:59 -0800
Subject: [PATCH] I think decompressor is written now.

---
 .../src/org/badvision/Lx47Algorithm.java      | 39 +++++------
 Platform/Apple/virtual/src/core/decomp.s      | 64 ++++++++++---------
 2 files changed, 55 insertions(+), 48 deletions(-)

diff --git a/Platform/Apple/tools/PackPartitions/src/org/badvision/Lx47Algorithm.java b/Platform/Apple/tools/PackPartitions/src/org/badvision/Lx47Algorithm.java
index 95956151..7bf6d13e 100644
--- a/Platform/Apple/tools/PackPartitions/src/org/badvision/Lx47Algorithm.java
+++ b/Platform/Apple/tools/PackPartitions/src/org/badvision/Lx47Algorithm.java
@@ -61,10 +61,10 @@ public class Lx47Algorithm
     int countLitBits(int lits) {
         if (lits == 0)
             return 0;
-        int bits = (lits * 8) + 1;
+        int bits = lits * 8;
         while (lits > 0) {
             int n = Math.min(255, lits);
-            bits += countGammaBits(n);
+            bits += 1 + countGammaBits(n);
             lits -= n;
         }
         return bits;
@@ -204,7 +204,12 @@ public class Lx47Algorithm
         }
         
         void writeLiteralLen(int value) {
-            writeGamma(value);
+            if (value == 0)
+                writeBit(0);
+            else {
+                writeBit(1);
+                writeGamma(value);
+            }
         }
 
         void writeCodePair(int matchLen, int offset) 
@@ -268,7 +273,6 @@ public class Lx47Algorithm
 
                 // Literal string
                 int pos = input_index - optimal[input_index].lits + 1;
-                w.writeBit((optimal[input_index].lits > 0) ? 1 : 0);
                 while (optimal[input_index].lits > 0) {
                     int n = Math.min(255, optimal[input_index].lits);
                     addDebug("lits l=%d", n);
@@ -347,7 +351,10 @@ public class Lx47Algorithm
         }
         
         int readLiteralLen() {
-            return readGamma();
+            if (readBit() == 0)
+                return 0;
+            else
+                return readGamma();
         }
 
         int readCodePair()
@@ -357,7 +364,7 @@ public class Lx47Algorithm
             int matchLen = 2;
             if ((data & 64) == 64)
                 offset |= readGamma() << 6;
-            offset++;
+            offset++; // important
             if ((data & 128) == 128)
                 matchLen += readGamma();
             return matchLen | (offset<<16); // pack both vals into a single int
@@ -384,20 +391,16 @@ public class Lx47Algorithm
         while (true) 
         {
             // Check for literal string
-            if (r.readBit() != 0) {
-                while (true) {
-                    len = r.readLiteralLen();
-                    chkDebug("lits l=%d", len);
-                    for (int i=0; i<len; i++) {
-                        output_data[outPos++] = (byte) r.readByte();
-                        chkDebug("lit $%x", output_data[outPos-1]);
-                    }
-                    if (len != 255)
-                        break;
+            while (true) {
+                len = r.readLiteralLen();
+                chkDebug("lits l=%d", len);
+                for (int i=0; i<len; i++) {
+                    output_data[outPos++] = (byte) r.readByte();
+                    chkDebug("lit $%x", output_data[outPos-1]);
                 }
+                if (len != 255)
+                    break;
             }
-            else
-                chkDebug("lits l=0");
             
             // Check for EOF at the end of each literal string
             if (outPos == outStart+outLen)
diff --git a/Platform/Apple/virtual/src/core/decomp.s b/Platform/Apple/virtual/src/core/decomp.s
index 7b6955cd..83912287 100644
--- a/Platform/Apple/virtual/src/core/decomp.s
+++ b/Platform/Apple/virtual/src/core/decomp.s
@@ -22,9 +22,13 @@
 ; Global definitions
 !source "../include/global.i"
 
-bits	= $B		; len 1
+tmp	= $2		; len 2
+pTmp	= $4		; len 2
+bits	= $6		; len 1
+
 pSrc	= $C		; len 2
 pDst	= $E		; len 2
+pEnd	= $10		; len 2
 
 ; Decompress from pSrc to pDst. They can overlap, as long as the source block
 ; ends (at least) 2 bytes beyond the end of the dest block, e.g.
@@ -33,28 +37,31 @@ pDst	= $E		; len 2
 ; This guarantees that the decompression won't overwrite any source material
 ; before it gets used.
 decomp	ldy #0		; invariant: Y=0 unless we're mid-copy
-	sty bits
+	beq .lits2	; always taken
 
 .lits	lsr bits
 	bne +
-	jsr getBits
+.lits2	jsr getBits
 +	bcc .seq
-.lits2	jsr rdGamma
+	jsr rdGamma
 	tax
+	cpx #255	; special case: long literal marked by len=255; chk and save to carry
 -	lda (pSrc),y
 	sta (pDst),y
-	iny
-	dex
+	inc pSrc
+	bne +
+	inc pSrc+1
++	inc pDst
+	bne +
+	inc pDst+1
++	dex
 	bne -
-	jsr advSrc
-	jsr advDst
-	iny		; special case: long literal string marked by len=255
-	beq .lits2
-	ldy #0		; back to invariant
-.endchk	cmp pEnd	; check for done at end of each literal string
+	bcs .lits	; (see special case above)
+.endchk	lda pDst+1
+	cmp pEnd+1	; check for done at end of each literal string
 	bcc .seq
-	lda pDst+1
-	cmp pEnd+1
+	lda pDst
+	cmp pEnd
 	bcc .seq
 	rts
 
@@ -96,10 +103,16 @@ decomp	ldy #0		; invariant: Y=0 unless we're mid-copy
 	iny
 	dex
 	bne -
-	jsr advDst
-	ldy #0
-	beq .lits	; always taken
+	tya
+	clc
+	adc pDst
+	sta pDst
+	ldy #0		; back to 0 as expected by lits section
+	bcc .lits
+	inc pDst+1
+	bcs .lits	; always taken
 
+; Read an Elias Gamma value into A. Destroys X. Sets carry.
 rdGamma	lda #1
 -	asl bits
 	bne +
@@ -109,10 +122,11 @@ rdGamma	lda #1
 	bne +
 	jsr getBits
 +	rol
-	bcc -		; always taken except if overflow error
+	bcc -		; always taken except if overflow error, in which case WTF.
 .ret	rts
 
-getBits	pha
+; Get another 8 bits into our bit buffer. Destroys X. Preserves A. Requires Y=0.
+getBits	tax
 	lda (pSrc),y
 	inc pSrc
 	bne +
@@ -120,15 +134,5 @@ getBits	pha
 +	sec
 	rol
 	sta bits
-	pla
+	txa
 	rts
-
-advDst	inx
-	inx
-advSrc	tya
-	clc
-	adc pSrc,x
-	sta pSrc,x
-	bcc +
-	inc pSrc+1,x
-+	rts