port tunnel example to C

examples/c/cart.c

@@ -0,0 +1,31 @@
+#define IMPORT(MODULE, NAME) __attribute__((import_module(MODULE), import_name(NAME)))
+
+IMPORT("env", "atan2") extern float atan2(float, float);
+IMPORT("env", "time") extern float time();
+
+int ftoi(float v) {
+    return __builtin_wasm_trunc_s_i32_f32(v);
+}
+
+float sqrt(float v) {
+    return __builtin_sqrt(v);
+}
+
+#define FRAMEBUFFER ((unsigned char*)120)
+
+void upd() {
+    int i = 0;
+
+    for( ;; ) {
+        float t = time() * 63.0f;
+        float x = (float)(i % 320 - 160);
+        float y = (float)(i / 320 - 120);
+        float d = 40000.0f / sqrt(x * x + y * y + 1.0f);
+        float u = atan2(x, y) * 512.0f / 3.141f;
+        unsigned char c = (unsigned char)(ftoi(d + t * 2.0f) ^ ftoi(u + t)) >> 4;
+        FRAMEBUFFER[i] = c;
+
+        i += 1;
+        if(i >= 320*240) break;
+    }
+}