better support for large dictionaries (> 128 KB)

2016-07-27 14:37:00 +02:00
parent 07626dfa51
commit c154d9d6a2
3 changed files with 37 additions and 31 deletions
@@ -230,4 +230,29 @@ void* ZSTD_defaultAllocFunction(void* opaque, size_t size);
 void ZSTD_defaultFreeFunction(void* opaque, void* address);
 static const ZSTD_customMem defaultCustomMem = { ZSTD_defaultAllocFunction, ZSTD_defaultFreeFunction, NULL };

+/*======  common function  ======*/
+
+MEM_STATIC U32 ZSTD_highbit32(U32 val)
+{
+#   if defined(_MSC_VER)   /* Visual */
+    unsigned long r=0;
+    _BitScanReverse(&r, val);
+    return (unsigned)r;
+#   elif defined(__GNUC__) && (__GNUC__ >= 3)   /* GCC Intrinsic */
+    return 31 - __builtin_clz(val);
+#   else   /* Software version */
+    static const int DeBruijnClz[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31 };
+    U32 v = val;
+    int r;
+    v |= v >> 1;
+    v |= v >> 2;
+    v |= v >> 4;
+    v |= v >> 8;
+    v |= v >> 16;
+    r = DeBruijnClz[(U32)(v * 0x07C4ACDDU) >> 27];
+    return r;
+#   endif
+}
+
+
 #endif   /* ZSTD_CCOMMON_H_MODULE */