Simpler PRNG and faster magics search

[stockfish] / src / misc.h

diff --git a/src/misc.h b/src/misc.h
index 34ef03259f9de5e6f1d75664aa0c16bef88f7e36..b9277372aa4ac224dd2c4baf68aebfceef64d711 100644 (file)
--- a/src/misc.h
+++ b/src/misc.h
@@ -46,7 +46,7 @@ namespace Time {
 template<class Entry, int Size>
 struct HashTable {
   HashTable() : table(Size, Entry()) {}
-  Entry* operator[](Key k) { return &table[(uint32_t)k & (Size - 1)]; }
+  Entry* operator[](Key key) { return &table[(uint32_t)key & (Size - 1)]; }
 
 private:
   std::vector<Entry> table;
@@ -59,4 +59,37 @@ std::ostream& operator<<(std::ostream&, SyncCout);
 #define sync_cout std::cout << IO_LOCK
 #define sync_endl std::endl << IO_UNLOCK
 
+
+/// xorshift64star Pseudo-Random Number Generator
+/// This class is based on original code written and dedicated
+/// to the public domain by Sebastiano Vigna (2014).
+/// It has the following characteristics:
+///  -  Outputs 64-bit numbers
+///  -  Passes Dieharder and SmallCrush test batteries
+///  -  Does not require warm-up, no zeroland to escape
+///  -  Internal state is a single 64-bit integer
+///  -  Period is 2^64 - 1
+///  -  Speed: 1.60 ns/call (Core i7 @3.40GHz)
+/// For further analysis see
+///   <http://vigna.di.unimi.it/ftp/papers/xorshift.pdf>
+
+class PRNG {
+
+  uint64_t x;
+
+  uint64_t rand64() {
+    x^=x>>12; x^=x<<25; x^=x>>27;
+    return x * 2685821657736338717LL;
+  }
+
+public:
+  PRNG(uint64_t seed) : x(seed) { assert(seed); }
+
+  template<typename T> T rand() { return T(rand64()); }
+
+  /// Special generator used to fast init magic numbers.
+  /// Output values only have 1/8th of their bits set on average.
+  template<typename T> T sparse_rand() { return T(rand64() & rand64() & rand64()); }
+};
+
 #endif // #ifndef MISC_H_INCLUDED