Better encoding of offset=64

Platform/Apple/tools/PackPartitions/src/org/badvision/Lx47Algorithm.java

@@ -50,9 +50,10 @@ public class Lx47Algorithm
     }
     
     int countCodePair(int prevLits, int matchLen, int offset) {
+        assert offset >= 1;
         int nBits = (prevLits>0 ? 0 : 1) 
                     + 8 // 8 for the byte that's always emitted
-                    + (offset>=64 ? countGammaBits(offset>>6) : 0)
+                    + ((offset-1)>=64 ? countGammaBits((offset-1)>>6) : 0)
                     + (matchLen>2 ? countGammaBits(matchLen-2) : 0);
         return nBits;
     }
@@ -60,10 +61,10 @@ public class Lx47Algorithm
     int countLitBits(int lits) {
         if (lits == 0)
             return 0;
-        int bits = lits * 8;
+        int bits = (lits * 8) + 1;
         while (lits > 0) {
             int n = Math.min(255, lits);
-            bits += 1 + countGammaBits(n);
+            bits += countGammaBits(n);
             lits -= n;
         }
         return bits;
@@ -203,16 +204,12 @@ public class Lx47Algorithm
         }
         
         void writeLiteralLen(int value) {
-            if (value == 0)
-                writeBit(0);
-            else {
-                writeBit(1);
-                writeGamma(value);
-            }
+            writeGamma(value);
         }
 
         void writeCodePair(int matchLen, int offset) 
         {
+            offset -= 1;
             int data = offset & 63; // 6 bits
 
             if (offset >= 64)
@@ -271,6 +268,7 @@ 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);
@@ -288,7 +286,7 @@ public class Lx47Algorithm
                 // Sequence. If two in a row, insert a zero-length lit str
                 if (!prevIsLit) {
                     addDebug("lits l=0");
-                    w.writeLiteralLen(0);
+                    w.writeBit(0);
                 }
                 
                 // Now write sequence info
@@ -304,7 +302,7 @@ public class Lx47Algorithm
         // EOF marker
         if (!prevIsLit) {
             addDebug("lits l=0");
-            w.writeLiteralLen(0);
+            w.writeBit(0);
         }
         addDebug("EOF");
 
@@ -349,8 +347,7 @@ public class Lx47Algorithm
         }
         
         int readLiteralLen() {
-            int b = readBit();
-            return (b==0) ? 0 : readGamma();
+            return readGamma();
         }
 
         int readCodePair()
@@ -360,9 +357,10 @@ public class Lx47Algorithm
             int matchLen = 2;
             if ((data & 64) == 64)
                 offset |= readGamma() << 6;
+            offset++;
             if ((data & 128) == 128)
                 matchLen += readGamma();
-            return matchLen | (offset<<16);
+            return matchLen | (offset<<16); // pack both vals into a single int
         }
     }
     
@@ -386,16 +384,20 @@ public class Lx47Algorithm
         while (true) 
         {
             // Check for literal string
-            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 (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;
                 }
-                if (len != 255)
-                    break;
             }
+            else
+                chkDebug("lits l=0");
             
             // Check for EOF at the end of each literal string
             if (outPos == outStart+outLen)

Platform/Apple/virtual/src/core/decomp.s

@@ -34,12 +34,13 @@ pDst	= $E		; len 2
 ; before it gets used.
 decomp	ldy #0		; invariant: Y=0 unless we're mid-copy
 	sty bits
-	beq .lits
 
-.lits	jsr rdGamma
+.lits	lsr bits
+	bne +
+	jsr getBits
++	bcc .seq
+.lits2	jsr rdGamma
 	tax
-	dex
-	beq +
 -	lda (pSrc),y
 	sta (pDst),y
 	iny
@@ -47,49 +48,49 @@ decomp	ldy #0		; invariant: Y=0 unless we're mid-copy
 	bne -
 	jsr advSrc
 	jsr advDst
-	cpy #254	; special case: long literal string
-	beq .lits
+	iny		; special case: long literal string marked by len=255
+	beq .lits2
 	ldy #0		; back to invariant
-.endchk	cmp pEnd
+.endchk	cmp pEnd	; check for done at end of each literal string
+	bcc .seq
 	lda pDst+1
-	sbc pEnd+1
+	cmp pEnd+1
 	bcc .seq
 	rts
 
 .seq	lda (pSrc),y
-	iny
-	asl
+	inc pSrc
+	bne +
+	inc pSrc+1
++	asl
 	php		; save high bit for later len check
-	asl
-	bcs .bigoff
-	lsr
+	bmi .bigoff
 	lsr
 	sta tmp
-	ldx #0
-	beq .gotoff	; always taken
-.bigoff	sta tmp
+	sty tmp+1	; zero
+	bcc .gotoff	; always taken
+.bigoff	asl
+	sta tmp
 	jsr rdGamma
 	lsr
 	rol tmp
 	lsr
 	rol tmp
-	tax
+	sta tmp+1
 .gotoff	lda pDst
-	sec
+	clc		; effectively add 1 to offset.
 	sbc tmp
 	sta pTmp
-	txa
-	eor #$FF
-	adc pDst+1
-	sta pDst+1
+	lda pDst+1
+	sbc tmp+1
+	sta pTmp+1
 .len	ldx #2
 	plp
 	bcc .gotlen
-	jsr rdGamma	; A>=1 + sec + 1 => final len 3 or more
-	adc #1
+	jsr rdGamma
+	adc #1		; A>=1 + sec + 1 => final len 3 or more
 	tax
-.gotlen	jsr advSrc
-	ldy #0
+.gotlen
 -	lda (pTmp),y
 	sta (pDst),y
 	iny
@@ -113,25 +114,21 @@ rdGamma	lda #1
 
 getBits	pha
 	lda (pSrc),y
-	iny
-	sec
+	inc pSrc
+	bne +
+	inc pSrc+1
++	sec
 	rol
 	sta bits
 	pla
 	rts
 
+advDst	inx
+	inx
 advSrc	tya
 	clc
-	adc pSrc
-	sta pSrc
+	adc pSrc,x
+	sta pSrc,x
 	bcc +
-	inc pSrc+1
-+	rts
-
-advDst	tya
-	clc
-	adc pDst
-	sta pDst
-	bcc +
-	inc pDst+1
+	inc pSrc+1,x
 +	rts