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Make Rust rotate code smaller #462

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merged 2 commits into from
Feb 15, 2019
Merged

Make Rust rotate code smaller #462

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bf66736
Make Rust rotate code smaller
surma Feb 14, 2019
2614c82
Back on the rust happy path
surma Feb 15, 2019
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2 changes: 2 additions & 0 deletions codecs/rotate/.gitignore
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
target
Cargo.lock
14 changes: 14 additions & 0 deletions codecs/rotate/Cargo.toml
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@@ -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"
11 changes: 5 additions & 6 deletions codecs/rotate/build.sh
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Expand Up @@ -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"
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29 changes: 19 additions & 10 deletions codecs/rotate/rotate.rs
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@@ -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) {
Expand Down Expand Up @@ -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));
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Won't this not compile in debug mode? I think you meant to name the unchecked_unwrap function unwrap_abort (and also make it non-unsafe).

This also looks pretty ugly. May I recommend an extension trait:

trait UnwrapHard {
  type Output;
  fn unwrap_hard(self) -> Self::Output;
}

impl<T> UnwrapHard for Option<T> {
    type Output = T;
    #[cfg(not(debug_assertions))]
    #[inline]
    fn unwrap_hard(self) -> T {
        use std::process;
        match self {
            Some(t) => t,
            None => process::abort(),
        }
    }
    
    #[cfg(debug_assertions)]
    fn unwrap_hard(self) -> T {
        self.unwrap()
    }
}

To see it in action, see the playground

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You are correct. The unsafe/misnaming was an oversight copy/pasting from @fitzgen lol. I’m working on a new PR anyways and we shipped the release build, so we are good for now 😅

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Also good shout on the trait. I’m gonna use that in the next PR. Thank you very much!

i += 1;
}
}
}

#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
loop {}
}
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