1 files changed, 74 insertions, 0 deletions
diff --git a/src/mersenne.cpp b/src/mersenne.cpp
new file mode 100644
index 000000000..bc4cb949a
--- /dev/null
+++ b/src/mersenne.cpp
@@ -0,0 +1,74 @@
+/* $Id$ */
+
+#include "stdafx.h"
+#include "openttd.h"
+
+#ifdef MERSENNE_TWISTER
+
+// Source code for Mersenne Twister.
+// A Random number generator with much higher quality random numbers.
+
+#define N              (624)                 // length of _mt_state vector
+#define M              (397)                 // a period parameter
+#define K              (0x9908B0DFU)         // a magic constant
+#define hiBit(u)       ((u) & 0x80000000U)   // mask all but highest   bit of u
+#define loBit(u)       ((u) & 0x00000001U)   // mask all but lowest    bit of u
+#define loBits(u)      ((u) & 0x7FFFFFFFU)   // mask     the highest   bit of u
+#define mixBits(u, v)  (hiBit(u)|loBits(v))  // move hi bit of u to hi bit of v
+
+static uint32   _mt_state[N+1];     // _mt_state vector + 1 extra to not violate ANSI C
+static uint32   *_mt_next;          // _mt_next random value is computed from here
+static int      _mt_left = -1;      // can *_mt_next++ this many times before reloading
+
+void SeedMT(uint32 seed)
+{
+    register uint32 x = (seed | 1U) & 0xFFFFFFFFU, *s = _mt_state;
+    register int    j;
+
+    for (_mt_left=0, *s++=x, j=N; --j;
+        *s++ = (x*=69069U) & 0xFFFFFFFFU);
+ }
+
+
+static uint32 ReloadMT(void)
+ {
+    register uint32 *p0=_mt_state, *p2=_mt_state+2, *pM=_mt_state+M, s0, s1;
+    register int    j;
+
+    if (_mt_left < -1)
+        SeedMT(4357U);
+
+    _mt_left=N-1, _mt_next=_mt_state+1;
+
+    for (s0=_mt_state[0], s1=_mt_state[1], j=N-M+1; --j; s0=s1, s1=*p2++)
+        *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
+
+    for (pM=_mt_state, j=M; --j; s0=s1, s1=*p2++)
+        *p0++ = *pM++ ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
+
+    s1=_mt_state[0], *p0 = *pM ^ (mixBits(s0, s1) >> 1) ^ (loBit(s1) ? K : 0U);
+    s1 ^= (s1 >> 11);
+    s1 ^= (s1 <<  7) & 0x9D2C5680U;
+    s1 ^= (s1 << 15) & 0xEFC60000U;
+    return(s1 ^ (s1 >> 18));
+ }
+
+
+uint32 RandomMT(void)
+{
+	uint32 y;
+
+	if (--_mt_left < 0)
+		return ReloadMT();
+
+	y  = *_mt_next++;
+	y ^= (y >> 11);
+	y ^= (y <<  7) & 0x9D2C5680U;
+	y ^= (y << 15) & 0xEFC60000U;
+	return y ^ (y >> 18);
+}
+#else
+
+void SeedMT(uint32 seed) {}
+
+#endif /* MERSENNE_TWISTER */