Fix: Random partitioner hash values should be in the range [1, 2^127-1]

Author: Michael Penick

src/md5.cpp

@@ -124,15 +124,6 @@ void Md5::final(uint8_t* result) {
   memset(this, 0, sizeof(Md5));
 }
 
-void Md5::final(uint64_t* hi, uint64_t* lo) {
-  final();
-
-  *hi = static_cast<uint64_t>(a_) << 32 | (static_cast<uint64_t>(b_) & 0xFFFFFFFF);
-  *lo  = static_cast<uint64_t>(c_) << 32 | (static_cast<uint64_t>(d_) & 0xFFFFFFFF);
-
-  memset(this, 0, sizeof(Md5));
-}
-
 void Md5::final() {
   unsigned long used, free;
 

src/token_map_impl.cpp

@@ -100,11 +100,45 @@ RandomPartitioner::Token RandomPartitioner::from_string(const StringRef& str) {
   return token;
 }
 
+uint64_t RandomPartitioner::encode(uint8_t* bytes) {
+  uint64_t result = 0;
+  const size_t num_bytes = sizeof(uint64_t);
+  for (size_t i = 0; i < num_bytes; ++i) {
+    result |= (static_cast<uint64_t>(bytes[i]) << (8 * (num_bytes - i - 1)));
+  }
+  return result;
+}
+
+RandomPartitioner::Token RandomPartitioner::abs(RandomPartitioner::Token token) {
+  if (token.hi & 0x8000000000000000ULL) {
+    token.hi = ~token.hi;
+    token.lo = ~token.lo;
+
+    uint64_t old_lo = token.lo;
+    ++token.lo;
+    // Carry to "hi" if our "lo" value wrapped
+    if(token.lo < old_lo) {
+      ++token.hi;
+    }
+  }
+  return token;
+}
+
 RandomPartitioner::Token RandomPartitioner::hash(const StringRef& str) {
   Md5 hash;
   hash.update(reinterpret_cast<const uint8_t*>(str.data()), str.size());
+  uint8_t digest[16];
+  hash.final(digest);
   Token token;
-  hash.final(&token.hi, &token.lo);
+
+  // For compatability with Cassandra we interpret the MD5 as a big-endian value:
+  // Reference: https://docs.oracle.com/javase/7/docs/api/java/math/BigInteger.html#BigInteger(byte[])
+  token.hi = encode(digest);
+  token.lo = encode(digest + 8);
+
+  // Then we find the absolute value of the two's complement representation.
+  token = abs(token);
+
   return token;
 }
 

src/token_map_impl.hpp

@@ -121,6 +121,9 @@ struct RandomPartitioner {
     }
   };
 
+  static Token abs(Token token);
+  static uint64_t encode(uint8_t* bytes);
+
   static Token from_string(const StringRef& str);
   static Token hash(const StringRef& str);
   static StringRef name() { return "RandomPartitioner"; }