Added : format description file

Added : new tuning parameter : LZ4_COMPRESSMIN. Thanks to Maciej Adamczyk for suggestion.
changed : macro for bswap16, in order to help GCC intrinsic detection. Thank to Erik Andersen for suggestion.

git-svn-id: https://lz4.googlecode.com/svn/trunk@57 650e7d94-2a16-8b24-b05c-7c0b3f6821cd

1 files changed, 12 insertions, 3 deletions

diff --git a/lz4.c b/lz4.c
index a131a81..cce3b17 100644
--- a/lz4.c
+++ b/lz4.c
@@ -45,6 +45,13 @@
 // The default value (6) is recommended

 #define NOTCOMPRESSIBLE_CONFIRMATION 6

 

+// LZ4_COMPRESSMIN :

+// Compression function will *fail* if it is not successful at compressing input by at least LZ4_COMPRESSMIN bytes

+// Since the compression function stops working prematurely, it results in a speed gain

+// The output however is unusable. Compression function result will be zero.

+// Default : 0 = disabled

+#define LZ4_COMPRESSMIN 0

+

 // BIG_ENDIAN_NATIVE_BUT_INCOMPATIBLE :

 // This will provide a boost to performance for big endian cpu, but the resulting compressed stream will be incompatible with little-endian CPU.

 // You can set this option to 1 in situations where data will stay within closed environment

@@ -92,13 +99,13 @@
 #endif

 

 #ifdef _MSC_VER

-#define inline __forceinline    // Visual is not C99, but supports inline

+#define inline __forceinline    // Visual is not C99, but supports some kind of inline

 #endif

 

 #ifdef _MSC_VER  // Visual Studio

-#define bswap16(i) _byteswap_ushort(i)

+#define bswap16(x) _byteswap_ushort(x)

 #else

-#define bswap16(i) (((i)>>8) | ((i)<<8))

+#define bswap16(x)  ((unsigned short int) ((((x) >> 8) & 0xffu) | (((x) & 0xffu) << 8)))

 #endif

 

 

@@ -429,6 +436,7 @@ _last_literals:
 	// Encode Last Literals

 	{

 		int lastRun = iend - anchor;

+		if ((LZ4_COMPRESSMIN>0) && (((op - (BYTE*)dest) + lastRun + 1 + ((lastRun-15)/255)) > isize - LZ4_COMPRESSMIN)) return 0;

 		if (lastRun>=(int)RUN_MASK) { *op++=(RUN_MASK<<ML_BITS); lastRun-=RUN_MASK; for(; lastRun > 254 ; lastRun-=255) *op++ = 255; *op++ = (BYTE) lastRun; }

 		else *op++ = (lastRun<<ML_BITS);

 		memcpy(op, anchor, iend - anchor);

@@ -570,6 +578,7 @@ _last_literals:
 	// Encode Last Literals

 	{

 		int lastRun = iend - anchor;

+		if ((LZ4_COMPRESSMIN>0) && (((op - (BYTE*)dest) + lastRun + 1 + ((lastRun-15)/255)) > isize - LZ4_COMPRESSMIN)) return 0;

 		if (lastRun>=(int)RUN_MASK) { *op++=(RUN_MASK<<ML_BITS); lastRun-=RUN_MASK; for(; lastRun > 254 ; lastRun-=255) *op++ = 255; *op++ = (BYTE) lastRun; }

 		else *op++ = (lastRun<<ML_BITS);

 		memcpy(op, anchor, iend - anchor);