Implemented a bucket/paritition distribution function in Request clas…

…s that hashes the underlying key id over a provided modulus. Currently uses the SHA1 algorithm.

Makefile

@@ -7,10 +7,10 @@ CXXFLAGS := -std=c++14 -Wall -g -pedantic-errors -Werror -O3 \
 # have the library and headers installed.
 REPLAY ?= no
 
-LDFLAGS :=
+LDFLAGS := -lcrypto -lssl -lpython2.7
 
 ifeq ($(REPLAY),yes)
-LDFLAGS += -lmemcached
+LDFLAGS += -lmemcached 
 else
 CXXFLAGS += -DNOREPLAY
 endif
@@ -25,7 +25,7 @@ all: lsm-sim
 	$(CXX) $(CXXFLAGS) -c $<
 
 lsm-sim: $(OBJS)
-	$(CXX) $(LDFLAGS) -o $@ $^ -lpython2.7
+	$(CXX) $(LDFLAGS) -o $@ $^ 
 
 clean:
 	-rm lsm-sim src/*.o

src/request.cpp

@@ -6,6 +6,8 @@
 #include "common.h"
 #include "request.h"
 
+#include "openssl/sha.h"
+
 Request::Request(const std::string& s)
   : time{}
   , key_sz{}
@@ -70,3 +72,27 @@ bool Request::operator<(const Request& other)
 {
   return time < other.time;
 }
+
+size_t Request::hash_key(const size_t modulus) const
+{
+  union Int_to_unsigned_char 
+  {
+    uint32_t int_value;                         
+    unsigned char char_value[sizeof(uint32_t)]; 
+  };
+
+  union Unsigned_char_to_size_t
+  {
+    unsigned char char_value[SHA_DIGEST_LENGTH];  // 20 bytes.
+    size_t   size_t_value;                        // 8 bytes on x86.
+  };
+
+  Int_to_unsigned_char input;
+  input.int_value = this->kid;
+  Unsigned_char_to_size_t output;
+  SHA_CTX context;
+  SHA1_Init(&context);
+  SHA1_Update(&context, input.char_value, sizeof(uint32_t));
+  SHA1_Final(output.char_value, &context);
+  return output.size_t_value % modulus;
+}

src/request.h

@@ -13,6 +13,14 @@ struct Request {
   int32_t get_frag() const;
   bool operator<(const Request& other);
 
+  // Given a modulus, computes the SHA hash of the key_id 'kid' that belongs to
+  // this 'Request' and returns the hash mod the provided modules. This is
+  // intended for uniformly distributing requests across buckets, partitions,
+  // etc. 
+  //
+  // @param modulus - number of buckets or partitions to mod the hash by.
+  size_t hash_key(const size_t modulus) const;
+
   enum req_type { GET = 1
                 , SET = 2
                 , DEL = 3