unsafe-libopus

This library is libopus 1.3.1 translated from C to unsafe Rust with the assistance of c2rust.

It is called "unsafe" libopus, because it still pretty much has the same shape as the C code and is full of "unsafe".

This translation still allows you to get rid of C compiler toolchain and use the library in a pure rust environment, without linker hackery & dynamic linking issues.

It also may potentially be a starting point for a more idiomatic rust implementation of libopus, though I am not sure if it is worth the effort.

Usage

To use this library use the fork of opus crate or smth [TODO].

Translation technique

Firstly, the libopus 1.3.1 was compiled with the following commands:

CC=clang ./configure --disable-shared --disable-stack-protector --enable-extra-programs --disable-doc --disable-asm --disable-rtcd --disable-intrinsics --disable-dependency-tracking--disable-maintainer-mode --enable-hardening
CC=clang compiledb make -j

Then, using the resulting compile_commands.json file, the C code was transpiled to rust with:

c2rust transpile compile_commands.json -o . --overwrite-existing --reorganize-definitions --emit-modules --translate-const-macros --emit-build-files

The resulting code was then manually reorganized, to remove all duplication of structures & eradicate the use of #[no_mangle] extern "C" functions: they are all linked with rust now and do not have to exported.

Some other refactorings include:

• separation of the test binaries from the library as "examples"
• removal of dependencies of libc functions in the library by defining their variants in the library (idea from unsafe-libyaml)
• removal of dependency on the libc crate by replacing the libc types with concrete rust types (libc::c_int -> i32, etc)
• removal of C varargs by replacing them with a custom VarArgs struct, as C variadics are not yet stable in rust. This turns the opus_*_ctl family of functions into macros

Performance

The library was translated without the use of inline assembly, processor intrinsics and runtime CPU detection, so it is not as fast as the original code right now. The C version with those features is about 20% faster than the rust version on my machine.