Add a `Porting Reminders` section to the README

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Matt Ickstadt 2016-08-21 13:31:08 -05:00
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@ -24,6 +24,20 @@ See [rust-lang/rust#35437][0].
[2]: https://github.com/rust-lang/compiler-rt/tree/8598065bd965d9713bfafb6c1e766d63a7b17b89/lib/builtins [2]: https://github.com/rust-lang/compiler-rt/tree/8598065bd965d9713bfafb6c1e766d63a7b17b89/lib/builtins
[3]: https://travis-ci.org/japaric/rustc-builtins [3]: https://travis-ci.org/japaric/rustc-builtins
### Porting Reminders
1. [Rust][4] and [C][5] have slightly different operator precedence. C evaluates comparisons (`== !=`) before bitwise operations (`& | ^`), while Rust evaluates the other way.
2. C assumes wrapping operations everywhere. Rust panics on overflow when in debug mode. Consider using the [Wrapping][6] type or the explicit [wrapping_*][7] functions where applicable.
3. Note [C implicit casts][8], especially integer promotion. Rust is much more explicit about casting, so be sure that any cast which affects the output is ported to the Rust implementation.
4. Rust has [many functions][9] for integer or floating point manipulation in the standard library. Consider using one of these functions rather than porting a new one.
[4]: https://doc.rust-lang.org/reference.html#operator-precedence
[5]: http://en.cppreference.com/w/c/language/operator_precedence
[6]: https://doc.rust-lang.org/core/num/struct.Wrapping.html
[7]: https://doc.rust-lang.org/std/primitive.i32.html#method.wrapping_add
[8]: http://en.cppreference.com/w/cpp/language/implicit_conversion
[9]: https://doc.rust-lang.org/std/primitive.i32.html
## Progress ## Progress
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