update rust example

examples/rust/readme.txt

@@ -5,8 +5,8 @@ A nightly rust compiler is needed for the unstable sqrtf32
 intrinsic.
 
 Simply compiling with rustc as shown in build.sh results in a
-342 byte tunnel.wasm. Using wasm-opt this can be reduced to
-243 bytes.
+371 byte tunnel.wasm. Using wasm-opt this can be reduced to
+260 bytes.
 
 When you disassemble this wasm file using wasm2wat you can see
 these globals and exports:
@@ -21,5 +21,5 @@ values that are not simple scalars (i32, f32, etc.). Since our
 code doesn't actually use any of that, we can just delete them
 in a text editor and assemble the code again with wat2wasm.
 
-This gives us a 199 byte wasm file. Running this through
-uw8-tool pack brings us to the final size of 137 bytes.
+This gives us a 216 byte wasm file. Running this through
+uw8 pack brings us to the final size of 119 bytes.

examples/rust/tunnel.rs

@@ -9,12 +9,20 @@ mod env {
     extern "C" {
         pub fn atan2(x: f32, y: f32) -> f32;
     }
+
+    extern "C" {
+        pub fn time() -> f32;
+    }
 }
 
 fn atan2(x: f32, y: f32) -> f32 {
     unsafe { env::atan2(x, y) }
 }
 
+fn time() -> f32 {
+    unsafe { env::time() }
+}
+
 fn sqrt(v: f32) -> f32 {
     unsafe { core::intrinsics::sqrtf32(v) }
 }
@@ -29,14 +37,14 @@ fn ftoi(v: f32) -> i32 {
 }
 
 #[no_mangle]
-pub fn tic(time: i32) {
+pub fn upd() {
     for i in 0..320 * 240 {
-        let t = time as f32 / 10 as f32;
+        let t = time() * 63 as f32;
         let x = (i % 320 - 160) as f32;
         let y = (i / 320 - 120) as f32;
         let d = 40000 as f32 / sqrt(x * x + y * y + 1 as f32);
         let u = atan2(x, y) * 512f32 / 3.141;
-        let c = (ftoi(d + t * 2 as f32) ^ ftoi(u + t)) as u8;
+        let c = (ftoi(d + t * 2 as f32) ^ ftoi(u + t)) as u8 >> 4;
         unsafe {
             *((120 + i) as *mut u8) = c;
         }