Make Rust rotate code smaller (GoogleChromeLabs#462)

* Make Rust rotate code smaller

* Back on the rust happy path

codecs/rotate/.gitignore

@@ -0,0 +1,2 @@
+target
+Cargo.lock

codecs/rotate/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "rotate"
+version = "0.1.0"
+authors = ["Surma <surma@google.com>"]
+edition = "2018"
+
+[lib]
+name = "rotate"
+path = "rotate.rs"
+crate-type = ["cdylib", "rlib"]
+
+[profile.release]
+lto = true
+opt-level = "s"

codecs/rotate/build.sh

@@ -7,12 +7,11 @@ echo "Compiling wasm"
 echo "============================================="
 (
   rustup run nightly \
-    rustc \
-    --target=wasm32-unknown-unknown \
-    -C opt-level=3 \
-    -o rotate.wasm \
-    rotate.rs
-    wasm-strip rotate.wasm
+    cargo build \
+    --target wasm32-unknown-unknown \
+    --release
+  cp target/wasm32-unknown-unknown/release/rotate.wasm .
+  wasm-strip rotate.wasm
 )
 echo "============================================="
 echo "Compiling wasm  done"

codecs/rotate/rotate.rs

@@ -1,8 +1,22 @@
-#![no_std]
-#![no_main]
+use std::slice::from_raw_parts_mut;
 
-use core::panic::PanicInfo;
-use core::slice::from_raw_parts_mut;
+// This function is taken from
+// https://rustwasm.github.io/book/reference/code-size.html
+#[cfg(not(debug_assertions))]
+#[inline]
+pub fn unwrap_abort<T>(o: Option<T>) -> T {
+    use std::process;
+    match o {
+        Some(t) => t,
+        None => process::abort(),
+    }
+}
+
+// Normal panic-y behavior for debug builds
+#[cfg(debug_assertions)]
+unsafe fn unchecked_unwrap<T>(o: Option<T>) -> T {
+    o.unwrap()
+}
 
 #[no_mangle]
 fn rotate(input_width: isize, input_height: isize, rotate: isize) {
@@ -69,13 +83,8 @@ fn rotate(input_width: isize, input_height: isize, rotate: isize) {
   for d2 in 0..d2_limit {
     for d1 in 0..d1_limit {
       let in_idx = (d1_start + d1 * d1_advance) * d1_multiplier + (d2_start + d2 * d2_advance) * d2_multiplier;
-      out_b[i as usize] = in_b[in_idx as usize];
+      *unwrap_abort(out_b.get_mut(i as usize)) = *unwrap_abort(in_b.get(in_idx as usize));
       i += 1;
     }
   }
 }
-
-#[panic_handler]
-fn panic(_info: &PanicInfo) -> ! {
-  loop {}
-}