X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Frkiss.h;h=154f3ca2d9252c5f1952498a8fd95b588c67e9d0;hp=22ab50378f8f87a4c972749db588ae7cbd7b523a;hb=55bd27b8f08a151128d7065fa2819aa3e9605299;hpb=4cd53b68d0cc75fdf8eac28daad680b974f56cf7

diff --git a/src/rkiss.h b/src/rkiss.h
index 22ab5037..154f3ca2 100644
--- a/src/rkiss.h
+++ b/src/rkiss.h
@@ -1,7 +1,7 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
+  Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -20,60 +20,54 @@
   available under the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
-
- ** A small "keep it simple and stupid" RNG with some fancy merits:
- **
- ** Quite platform independent
- ** Passes ALL dieharder tests! Here *nix sys-rand() e.g. fails miserably:-)
- ** ~12 times faster than my *nix sys-rand()
- ** ~4 times faster than SSE2-version of Mersenne twister
- ** Average cycle length: ~2^126
- ** 64 bit seed
- ** Return doubles with a full 53 bit mantissa
- ** Thread safe
- **
- ** (c) Heinz van Saanen
-
 */
 
 #if !defined(RKISS_H_INCLUDED)
 #define RKISS_H_INCLUDED
 
-
-////
-//// Includes
-////
-
 #include "types.h"
 
-
-////
-//// Types
-////
+/// RKISS is our pseudo random number generator (PRNG) used to compute hash keys.
+/// George Marsaglia invented the RNG-Kiss-family in the early 90's. This is a
+/// specific version that Heinz van Saanen derived from some public domain code
+/// by Bob Jenkins. Following the feature list, as tested by Heinz.
+///
+/// - Quite platform independent
+/// - Passes ALL dieharder tests! Here *nix sys-rand() e.g. fails miserably:-)
+/// - ~12 times faster than my *nix sys-rand()
+/// - ~4 times faster than SSE2-version of Mersenne twister
+/// - Average cycle length: ~2^126
+/// - 64 bit seed
+/// - Return doubles with a full 53 bit mantissa
+/// - Thread safe
 
 class RKISS {
 
   // Keep variables always together
   struct S { uint64_t a, b, c, d; } s;
 
-  // Return 64 bit unsigned integer in between [0,2^64-1]
+  uint64_t rotate(uint64_t x, uint64_t k) const {
+    return (x << k) | (x >> (64 - k));
+  }
+
+  // Return 64 bit unsigned integer in between [0, 2^64 - 1]
   uint64_t rand64() {
 
-      const uint64_t
-        e = s.a - ((s.b <<  7) | (s.b >> 57));
-      s.a = s.b ^ ((s.c << 13) | (s.c >> 51));
-      s.b = s.c + ((s.d << 37) | (s.d >> 27));
-      s.c = s.d + e;
-      return s.d = e + s.a;
+    const uint64_t
+      e = s.a - rotate(s.b,  7);
+    s.a = s.b ^ rotate(s.c, 13);
+    s.b = s.c + rotate(s.d, 37);
+    s.c = s.d + e;
+    return s.d = e + s.a;
   }
 
   // Init seed and scramble a few rounds
   void raninit() {
 
-      s.a = 0xf1ea5eed;
-      s.b = s.c = s.d = 0xd4e12c77;
-      for (uint64_t i = 0; i < 73; i++)
-          rand64();
+    s.a = 0xf1ea5eed;
+    s.b = s.c = s.d = 0xd4e12c77;
+    for (int i = 0; i < 73; i++)
+        rand64();
   }
 
 public: