small compression speed improvement

git-svn-id: https://lz4.googlecode.com/svn/trunk@19 650e7d94-2a16-8b24-b05c-7c0b3f6821cd

1 files changed, 29 insertions, 24 deletions

diff --git a/lz4.c b/lz4.c
index bba9690..1fa9aa1 100644
--- a/lz4.c
+++ b/lz4.c
@@ -66,7 +66,7 @@
 // Constants

 //**************************************

 #define MINMATCH 4

-#define INCOMPRESSIBLE 128

+#define SKIPSTRENGTH 6

 

 #define MAXD_LOG 16

 #define MAX_DISTANCE ((1 << MAXD_LOG) - 1)

@@ -85,7 +85,7 @@
 //**************************************

 struct refTables

 {

-	BYTE* hashTable[HASHTABLESIZE];

+	const BYTE* hashTable[HASHTABLESIZE];

 };

 

 

@@ -107,20 +107,21 @@ int LZ4_compressCtx(void** ctx,
 				 int isize)

 {	

 	struct refTables *srt = (struct refTables *) (*ctx);

-	BYTE**  HashTable;

+	const BYTE**  HashTable;

 

-	BYTE	*ip = (BYTE*) source,       

-			*anchor = ip,

-			*incompressible = anchor + INCOMPRESSIBLE,

-			*iend = ip + isize,

-			*ilimit = iend - MINMATCH;

+	const BYTE* ip = (BYTE*) source;       

+	const BYTE* anchor = ip;

+	const BYTE* ref;

+	const BYTE* const iend = ip + isize;

+	const BYTE* const ilimit = iend - MINMATCH;

 

-	BYTE	*op = (BYTE*) dest,  

-			*ref,

-			*orun, *l_end;

+	BYTE* op = (BYTE*) dest;

+	BYTE* orun;

+	BYTE* l_end;

 	

-	int		len, length;

-	U32		step=1;

+	int len, length;

+	const int skipStrength = SKIPSTRENGTH;

+	U32 skipped = 1U << skipStrength;

 

 

 	// Init 

@@ -133,19 +134,14 @@ int LZ4_compressCtx(void** ctx,
 	memset(HashTable, 0, sizeof(srt->hashTable));

 

 	// Main Loop

-	while (ip < ilimit)

+	while (ip < ilimit+1)

 	{

 		ref = HashTable[HASH_VALUE(ip)];

 		HashTable[HASH_VALUE(ip)] = ip;

 

 		// Min Match

-		if ((ref < ip - MAX_DISTANCE) || (*(U32*)ref != *(U32*)ip))

-		{ 

-			if (ip>incompressible) { incompressible += INCOMPRESSIBLE << (step >> 1); step++; }

-			ip+=step; 

-			continue; 

-		}

-		step=1;

+		if ((ref < ip - MAX_DISTANCE) || (*(U32*)ref != *(U32*)ip)) { ip += (skipped++) >> skipStrength ; continue; }

+		skipped = (1U << skipStrength) + 3;

 

 		// Catch up

 		while ((ip>anchor) && (ref>(BYTE*)source) && (ip[-1]==ref[-1])) { ip--; ref--; }  

@@ -161,6 +157,7 @@ int LZ4_compressCtx(void** ctx,
 		do { *(U32*)op = *(U32*)anchor; op+=4; anchor+=4; } while (op<l_end) ;

 		op = l_end;

 

+_next_match:

 		// Encode Offset

 		*(U16*)op = (ip-ref); op+=2;

 

@@ -181,11 +178,18 @@ _endCount:
 		

 		// Encode MatchLength

 		if (len>=(int)ML_MASK) { *orun+=ML_MASK; len-=ML_MASK; for(; len > 509 ; len-=510) { *op++ = 255; *op++ = 255; } if (len > 254) { len-=255; *op++ = 255; } *op++ = (BYTE)len; } 

-		else *orun += len;			

+		else *orun += len;	

+

+		// Test end of chunk

+		if (ip > ilimit) { anchor = ip;  break; }

+

+		// Test next position

+		ref = HashTable[HASH_VALUE(ip)];

+		HashTable[HASH_VALUE(ip)] = ip;

+		if ((ref > ip - (MAX_DISTANCE + 1)) && (*(U32*)ref == *(U32*)ip)) { orun = op++; *orun=0; goto _next_match; }

 

 		// Prepare next loop

-		anchor = ip; 

-		incompressible = anchor + INCOMPRESSIBLE;

+		anchor = ip++; 

 	}

 

 	// Encode Last Literals

@@ -204,6 +208,7 @@ _endCount:
 }

 

 

+

 int LZ4_compress(char* source, 

 				 char* dest,

 				 int isize)