wip demo mode

src/rand.c

@@ -0,0 +1,31 @@
+#include "rand.h"
+
+static unsigned long long mcg_state = 0xcafef00dd15ea5e5u; // Must be odd
+static unsigned long long const multiplier = 6364136223846793005u;
+
+// https://en.wikipedia.org/wiki/Permuted_congruential_generator
+static unsigned long rand(void) {
+  unsigned long long x = mcg_state;
+  unsigned count = (unsigned)(x >> 61);
+
+  mcg_state = x * multiplier;
+  x ^= x >> 22;
+  return (unsigned long)(x >> (22 + count));
+}
+
+void set_seed(unsigned long long seed) {
+  mcg_state = 2 * seed + 1;
+  (void)rand();
+}
+
+unsigned char rand_uchar(const unsigned int max) {
+  return max == 0 ? 0 : (unsigned char)(rand() % max);
+}
+
+unsigned short rand_ushort(const unsigned int max) {
+  return max == 0 ? 0 : (unsigned short)(rand() % max);
+}
+
+unsigned int rand_uint(const unsigned int max) {
+  return max == 0 ? 0 : (unsigned int)(rand() % max);
+}