Espresso 0.0.2c

lib/math/random.c

@@ -0,0 +1,79 @@
+#include <types.h>
+
+#include <math/random.h>
+
+
+/*
+  This code uses Xorshift (high speed, small) and PCG (Permuted Congruential Generator).
+  PCG may or may not be slightly slower than Xorshift.
+*/
+
+static uint32_t xorshift_state = 2463534242;
+
+static void srand_xorshift(uint32_t seed)
+{
+  xorshift_state = seed;
+}
+
+static inline uint32_t rand_xorshift(void)
+{
+  uint32_t x = xorshift_state;
+  x ^= x << 13;
+  x ^= x >> 17;
+  x ^= x << 5;
+  
+  return xorshift_state = x;
+}
+
+static uint64_t state = 0x853c49e6748fea9bULL;
+static uint64_t inc   = 0xda3e39cb94b95bdbULL;
+
+static inline uint32_t rand_pcg32(void)
+{
+  uint64_t oldstate = state;
+  state = oldstate * 6364136223846793005ULL + (inc | 1);
+  uint32_t xorshifted = ((oldstate >> 18u) ^ oldstate) >> 27u;
+  uint32_t rot = oldstate >> 59u;
+  
+  return (xorshifted >> rot) | (xorshifted << ((-rot) & 31));
+}
+
+void seed_rand(uint32_t seed)
+{
+  srand_xorshift(seed);
+  state = seed * 6364136223846793005ULL + (seed | 1);
+}
+
+uint32_t uirand(void)
+{
+  return rand_pcg32() ^ rand_xorshift();
+}
+
+/* get a number between 0 and max-1 */
+uint32_t uirand_range(uint32_t max)
+{
+  if (max == 0)
+  {
+    return 0;
+  }
+
+  return uirand() % max;
+}
+
+uint64_t ulrand(void)
+{
+  uint64_t hi = uirand();
+  uint64_t lo = uirand();
+  return (hi << 32) | lo;
+}
+
+/* get a number between 0 and max-1 */
+uint64_t ulrand_range(uint64_t max)
+{
+  if (max == 0)
+  {
+    return 0;
+  }
+
+  return ulrand() % max;
+}