Replace the existing PRNG (Xorshift31) with (minimal) PCG (XSH-RR variant with 32-bit output, 64-bit state).

PCG is better than many alternatives by many metrics (see www.pcg-random.org) including statistical quality with good speed.

1 files changed, 15 insertions, 0 deletions

diff --git a/core/math/pcg.cpp b/core/math/pcg.cpp
new file mode 100644
index 0000000000..eac3b36d36
--- /dev/null
+++ b/core/math/pcg.cpp
@@ -0,0 +1,15 @@
+// *Really* minimal PCG32 code / (c) 2014 M.E. O'Neill / pcg-random.org
+// Licensed under Apache License 2.0 (NO WARRANTY, etc. see website)
+
+#include "pcg.h"
+
+uint32_t pcg32_random_r(pcg32_random_t* rng)
+{
+    uint64_t oldstate = rng->state;
+    // Advance internal state
+    rng->state = oldstate * 6364136223846793005ULL + (rng->inc|1);
+    // Calculate output function (XSH RR), uses old state for max ILP
+    uint32_t xorshifted = ((oldstate >> 18u) ^ oldstate) >> 27u;
+    uint32_t rot = oldstate >> 59u;
+    return (xorshifted >> rot) | (xorshifted << ((-rot) & 31));
+}