initial commit, 4.5 stable

thirdparty/misc/pcg.cpp

@@ -0,0 +1,58 @@
+// *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));
+}
+
+// Source from http://www.pcg-random.org/downloads/pcg-c-basic-0.9.zip
+void pcg32_srandom_r(pcg32_random_t* rng, uint64_t initstate, uint64_t initseq)
+{
+    rng->state = 0U;
+    rng->inc = (initseq << 1u) | 1u;
+    pcg32_random_r(rng);
+    rng->state += initstate;
+    pcg32_random_r(rng);
+}
+
+// Source from https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.c
+// pcg32_boundedrand_r(rng, bound):
+//     Generate a uniformly distributed number, r, where 0 <= r < bound
+uint32_t pcg32_boundedrand_r(pcg32_random_t *rng, uint32_t bound) {
+	// To avoid bias, we need to make the range of the RNG a multiple of
+	// bound, which we do by dropping output less than a threshold.
+	// A naive scheme to calculate the threshold would be to do
+	//
+	//     uint32_t threshold = 0x100000000ull % bound;
+	//
+	// but 64-bit div/mod is slower than 32-bit div/mod (especially on
+	// 32-bit platforms).  In essence, we do
+	//
+	//     uint32_t threshold = (0x100000000ull-bound) % bound;
+	//
+	// because this version will calculate the same modulus, but the LHS
+	// value is less than 2^32.
+	uint32_t threshold = -bound % bound;
+
+	// Uniformity guarantees that this loop will terminate.  In practice, it
+	// should usually terminate quickly; on average (assuming all bounds are
+	// equally likely), 82.25% of the time, we can expect it to require just
+	// one iteration.  In the worst case, someone passes a bound of 2^31 + 1
+	// (i.e., 2147483649), which invalidates almost 50% of the range.  In
+	// practice, bounds are typically small and only a tiny amount of the range
+	// is eliminated.
+	for (;;) {
+		uint32_t r = pcg32_random_r(rng);
+		if (r >= threshold)
+			return r % bound;
+	}
+}