optimized small key hashes by using bzhi instead of the switch construct

src/MurmurHash2.cpp

@@ -12,6 +12,11 @@
 // 1. It will not work incrementally.
 // 2. It will not produce the same results on little-endian and big-endian
 //    machines.
+//
+//changes for MurmurHash64A - small key hashes optimizations 
+//Copyright (C) <2021> Intel Corporation
+//SPDX-License-Identifier: MIT
+
 
 #include "MurmurHash2.h"
 
@@ -97,6 +102,7 @@ uint64_t MurmurHash64A ( const void * key, int len, uint64_t seed )
 {
   const uint64_t m = BIG_CONSTANT(0xc6a4a7935bd1e995);
   const int r = 47;
+  unsigned int c = 0;
 
   uint64_t h = seed ^ (len * m);
 
@@ -107,35 +113,39 @@ uint64_t MurmurHash64A ( const void * key, int len, uint64_t seed )
   {
     uint64_t k = *data++;
 
-    k *= m; 
-    k ^= k >> r; 
-    k *= m; 
-    
+    k *= m;
+    k ^= k >> r;
+    k *= m;
+
     h ^= k;
-    h *= m; 
+    h *= m;
   }
-
+ 
   const unsigned char * data2 = (const unsigned char*)data;
-
-  switch(len & 7)
+  uint64_t pIntData; 
+  c = len & 7;
+  if (c!=0)
   {
-  case 7: h ^= uint64_t(data2[6]) << 48;
-  case 6: h ^= uint64_t(data2[5]) << 40;
-  case 5: h ^= uint64_t(data2[4]) << 32;
-  case 4: h ^= uint64_t(data2[3]) << 24;
-  case 3: h ^= uint64_t(data2[2]) << 16;
-  case 2: h ^= uint64_t(data2[1]) << 8;
-  case 1: h ^= uint64_t(data2[0]);
-          h *= m;
-  };
-
+  		pIntData = *((uint64_t*)data2);
+	        pIntData &= (1ULL<<(c*8))-1;	
+  		h ^= pIntData;
+		h *= m;
+
+  }
+
+
   h ^= h >> r;
   h *= m;
   h ^= h >> r;
 
   return h;
-} 
 
+}
+
+
+///////////////////////////////////////////
+//
+///////////////////////////////////////////
 
 // 64-bit hash for 32-bit platforms
 

src/MurmurHash3.cpp

@@ -6,6 +6,10 @@
 // algorithms are optimized for their respective platforms. You can still
 // compile and run any of them on any platform, but your performance with the
 // non-native version will be less than optimal.
+//
+//changes for MurmurHash3_x64_128 - small key hashes optimizations
+//Copyright (C) <2021> Intel Corporation
+//SPDX-License-Identifier: MIT
 
 #include "MurmurHash3.h"
 
@@ -258,6 +262,8 @@ void MurmurHash3_x64_128 ( const void * key, const int len,
   const uint8_t * data = (const uint8_t*)key;
   const int nblocks = len / 16;
 
+  unsigned int c = 0;
+
   uint64_t h1 = seed;
   uint64_t h2 = seed;
 
@@ -288,34 +294,23 @@ void MurmurHash3_x64_128 ( const void * key, const int len,
 
   const uint8_t * tail = (const uint8_t*)(data + nblocks*16);
 
-  uint64_t k1 = 0;
-  uint64_t k2 = 0;
+  uint64_t k1_02 = 0;
+  uint64_t k2_02 = 0;
 
-  switch(len & 15)
+  c = len & 15;
+  if (c!=0)
   {
-  case 15: k2 ^= ((uint64_t)tail[14]) << 48;
-  case 14: k2 ^= ((uint64_t)tail[13]) << 40;
-  case 13: k2 ^= ((uint64_t)tail[12]) << 32;
-  case 12: k2 ^= ((uint64_t)tail[11]) << 24;
-  case 11: k2 ^= ((uint64_t)tail[10]) << 16;
-  case 10: k2 ^= ((uint64_t)tail[ 9]) << 8;
-  case  9: k2 ^= ((uint64_t)tail[ 8]) << 0;
-           k2 *= c2; k2  = ROTL64(k2,33); k2 *= c1; h2 ^= k2;
-
-  case  8: k1 ^= ((uint64_t)tail[ 7]) << 56;
-  case  7: k1 ^= ((uint64_t)tail[ 6]) << 48;
-  case  6: k1 ^= ((uint64_t)tail[ 5]) << 40;
-  case  5: k1 ^= ((uint64_t)tail[ 4]) << 32;
-  case  4: k1 ^= ((uint64_t)tail[ 3]) << 24;
-  case  3: k1 ^= ((uint64_t)tail[ 2]) << 16;
-  case  2: k1 ^= ((uint64_t)tail[ 1]) << 8;
-  case  1: k1 ^= ((uint64_t)tail[ 0]) << 0;
-           k1 *= c1; k1  = ROTL64(k1,31); k1 *= c2; h1 ^= k1;
-  };
+	uint64_t pIntData = *(const uint64_t *)(data + nblocks * 16 + 8);
+	pIntData &= (1ULL<<(((c>>3)*(c%8))*8))-1;
+ 	k2_02 ^= pIntData; k2_02 *= c2; k2_02  = ROTL64(k2_02,33); k2_02 *= c1; h2 ^= k2_02;
+
+	uint64_t pIntData2 = *(const uint64_t *)(data + nblocks * 16);
+	pIntData2 &= (1ULL<<(c*8))-1;
+ 	k1_02 ^= pIntData2; k1_02 *= c1; k1_02  = ROTL64(k1_02,31);k1_02 *= c2; h1 ^= k1_02;
+  }
 
   //----------
   // finalization
-
   h1 ^= len; h2 ^= len;
 
   h1 += h2;