diff options
Diffstat (limited to 'lz4.c')
| -rw-r--r-- | lz4.c | 36 |
1 files changed, 27 insertions, 9 deletions
@@ -44,10 +44,26 @@ /* * CPU_HAS_EFFICIENT_UNALIGNED_MEMORY_ACCESS : - * You can force the code to use unaligned memory access, should you know your CPU can handle it efficiently. - * If it effectively results in better speed (up to 50% improvement can be expected) + * By default, the source code expects the compiler to correctly optimize + * 4-bytes and 8-bytes read on architectures able to handle it efficiently. + * This is not always the case. In some circumstances (ARM notably), + * the compiler will issue cautious code even when target is able to correctly handle unaligned memory accesses. + * + * You can force the compiler to use unaligned memory access by uncommenting the line below. + * One of the below scenarios will happen : + * 1 - Your target CPU correctly handle unaligned access, and was not well optimized by compiler (good case). + * You will witness large performance improvements (+50% and up). + * Keep the line uncommented and send a word to upstream (https://groups.google.com/forum/#!forum/lz4c) + * The goal is to automatically detect such situations by adding your target CPU within an exception list. + * 2 - Your target CPU correctly handle unaligned access, and was already correctly optimized by compiler + * No change will be experienced. + * 3 - Your target CPU inefficiently handle unaligned access. + * You will experience a performance loss. Comment back the line. + * 4 - Your target CPU does not handle unaligned access. + * Program will crash. + * If it effectively results in better speed (case 1) * please report your configuration to upstream (https://groups.google.com/forum/#!forum/lz4c) - * so that an automatic detection macro can be added to mainline. + * so that an automatic detection macro can be added for future versions of the library. */ /* #define CPU_HAS_EFFICIENT_UNALIGNED_MEMORY_ACCESS 1 */ @@ -58,7 +74,7 @@ /* * Automated efficient unaligned memory access detection * Based on known hardware architectures - * This list will be updated thanks to Open Source community feedbacks + * This list will be updated thanks to feedbacks */ #if defined(CPU_HAS_EFFICIENT_UNALIGNED_MEMORY_ACCESS) \ || defined(__ARM_FEATURE_UNALIGNED) \ @@ -71,7 +87,10 @@ # define LZ4_UNALIGNED_ACCESS 0 #endif -/* Define this parameter if your target system or compiler does not support hardware bit count */ +/* + * LZ4_FORCE_SW_BITCOUNT + * Define this parameter if your target system or compiler does not support hardware bit count + */ #if defined(_MSC_VER) && defined(_WIN32_WCE) /* Visual Studio for Windows CE does not support Hardware bit count */ # define LZ4_FORCE_SW_BITCOUNT #endif @@ -88,7 +107,7 @@ #ifdef _MSC_VER /* Visual Studio */ # define FORCE_INLINE static __forceinline -# include <intrin.h> /* For Visual 2005 */ +# include <intrin.h> # pragma warning(disable : 4127) /* disable: C4127: conditional expression is constant */ #else # ifdef __GNUC__ @@ -961,7 +980,6 @@ FORCE_INLINE int LZ4_decompress_generic( } LZ4_wildCopy(op, ip, cpy); ip += length; op = cpy; - //LZ4_WILDCOPY(op, ip, cpy); ip -= (op-cpy); op = cpy; /* get offset */ match = cpy - LZ4_readLE16(ip); ip+=2; @@ -1018,7 +1036,7 @@ FORCE_INLINE int LZ4_decompress_generic( /* copy repeated sequence */ cpy = op + length; - if (unlikely((op-match)<(int)STEPSIZE)) + if (unlikely((op-match)<8)) { const size_t dec64 = dec64table[op-match]; op[0] = match[0]; @@ -1036,7 +1054,7 @@ FORCE_INLINE int LZ4_decompress_generic( if (op < oend-8) { LZ4_wildCopy(op, match, oend-8); - match += oend-8 - op; + match += (oend-8) - op; op = oend-8; } while (op<cpy) *op++ = *match++; |