Add linear feedback shift register to generate "random" numbers.

src/lfsr.c

@@ -0,0 +1,14 @@
+#include "lfsr.h"
+
+void lfsr_init(Lfsr *ctx, uint16_t init) {
+    ctx->lfsr = init;
+    ctx->bit = 0;
+}
+
+uint16_t lfsr_next(Lfsr *ctx) {
+    ctx->bit = ((ctx->lfsr >> 0) ^ (ctx->lfsr >> 2) ^ (ctx->lfsr >> 3) ^
+                (ctx->lfsr >> 5)) &
+               1U;
+    ctx->lfsr = (ctx->lfsr >> 1) | (ctx->bit << 15);
+    return ctx->lfsr;
+}

src/lfsr.h

@@ -0,0 +1,14 @@
+#ifndef LFSR_H
+#define LFSR_H
+
+#include <stdint.h>
+
+typedef struct Lfsr {
+    uint16_t lfsr;
+    uint16_t bit;
+} Lfsr;
+
+void lfsr_init(Lfsr *ctx, uint16_t init);
+uint16_t lfsr_next(Lfsr *ctx);
+
+#endif // LFSR_H