build: move map & rng logic to their own libraries

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I1802469f3baff4576f61accfb5a197d86a6a6964

libs/rng/rng.c

@@ -0,0 +1,22 @@
+#include "rng.h"
+
+// Linear congruential generator (LCG) state
+static unsigned int g_seed = 1;
+
+// LCG parameters (from numerical recipes)
+#define LCG_A 1664525
+#define LCG_C 1013904223
+#define LCG_MOD 4294967294  // 2^32 - 2 (avoid 0)
+
+void rng_seed(unsigned int seed) {
+  // Ensure seed is never 0
+  g_seed = (seed == 0) ? 1 : seed;
+}
+
+int rng_int(int min, int max) {
+  // Generate next value
+  g_seed = (LCG_A * g_seed + LCG_C) % LCG_MOD;
+
+  // Map to [min, max] range
+  return min + (int)((unsigned long long)g_seed % (max - min + 1));
+}

libs/rng/rng.h

@@ -0,0 +1,10 @@
+#ifndef RNG_H
+#define RNG_H
+
+// Seed the RNG with a deterministic value
+void rng_seed(unsigned int seed);
+
+// Get a random integer in range [min, max]
+int rng_int(int min, int max);
+
+#endif  // RNG_H