add simple rust example

examples/rust/tunnel.rs

@@ -0,0 +1,31 @@
+#![no_std]
+#![feature(core_intrinsics)]
+
+#[link(wasm_import_module = "math")]
+extern "C" {
+    fn atan2(x: f32, y: f32) -> f32;
+}
+
+fn sqrt(v: f32) -> f32 {
+    unsafe { core::intrinsics::sqrtf32(v) }
+}
+
+#[no_mangle]
+pub fn tic(time: i32) {
+    unsafe {
+        for i in 0..320 * 256 {
+            let t = time as f32 / 10 as f32;
+            let x = (i % 320 - 160) as f32;
+            let y = (i / 320 - 128) as f32;
+            let d = 20000 as f32 / sqrt(x * x + y * y + 1 as f32);
+            let u = atan2(x, y) * 512f32 / 3.141;
+            let c = ((d + t).to_int_unchecked::<i32>() ^ (u + t).to_int_unchecked::<i32>()) as u8;
+            *((120 + i) as *mut u8) = c;
+        }
+    }
+}
+
+#[panic_handler]
+fn panic(_: &core::panic::PanicInfo) -> ! {
+    loop {}
+}