4 ms·

I have currently got some bit-swizzling [1] going on to fit the concept of a Piece into u8. (one of 6 colours and one of 6 shapes). I'd like to turn this back

I have currently got some bit-swizzling [1] going on to fit the concept of a Piece into u8. (one of 6 colours and one of 6 shapes). I'd like to turn this back into a nice enum if I can! Introducing laziness by writing an iterator was actually one of the biggest single improvements (I couldn't figure out the syntax for a while, but lifetimes worked much better than I was expecting)! [1]: https://github.com/iamdanfox/qwirkler/blob/master/src/piece.rs https://github.com/iamdanfox/qwirkler/blob/master/src/piece....

kibwen 12y ago
Hm, an enum like `enum Color { R, O, Y, G, B, I, V }` is represented by a u8 at runtime (see for yourself here: http://is.gd/YkUY0l http://is.gd/YkUY0l), which means that you're only saving a single byte in your `Piece` struct by doing that manual optimization. What was the magnitude of the speedup that you saw?
Gankro 12y ago
There have been a few proposals for advanced bit-packing stuff, but most of it has been postponed as back-compat for later. That said, by default enum/struct layout is undefined, so it's possible the compiler could be taught to optimize your usecase correctly. For instance Option<&T> is the same size as &T because &T is strictly non-zero, and we can therefore use 0 for None.
kaoD 12y ago
Check kibwen's post (my sibling). It's [dead] for some reason but it answers your question. I'll reproduce it here: > Hm, an enum like `enum Color { R, O, Y, G, B, I, V }` is represented by a u8 at runtime (see for yourself here: http://is.gd/YkUY0l http://is.gd/YkUY0l), which means that you're only saving a single byte in your `Piece` struct by doing that manual optimization. What was the magnitude of the speedup that you saw?
nightpool 12y ago
FYI both kaoD and Kibwen's post seem to be dead because they included a link to a URL shortener (seems a little melodramatic on HNs part...) so I'll reproduce it here w/o the URL shortlink and see if that helps >Hm, an enum like `enum Color { R, O, Y, G, B, I, V }` is represented by a u8 at runtime (see for yourself here[1]), which means that you're only saving a single byte in your `Piece` struct by doing that manual optimization. What was the magnitude of the speedup that you saw? [1]: http://play.rust-lang.org/?code=%23%5Ballow(dead_code)%5D%0Aenum%20Color%20%7B%20R%2C%20O%2C%20Y%2C%20G%2C%20B%2C%20I%2C%20V%20%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20println!(%22%7B%7D%22%2C%20std%3A%3Amem%3A%3Asize_of%3A%3A%3CColor%3E())%3B%20%20%2F%2F%20size%20in%20bytes%0A%7D http://play.rust-lang.org/?code=%23%5Ballow(dead_code)%5D%0A...
- iamdanfox 12y ago
  Ah that's good to know, looks like I should switch it back! The manual u8 stuff was pretty marginal. (It was also before I discovered the `PartialEq` and `Copy` traits, so please forgive my Rust inexperience!)
deleted 12y ago
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kibwen 12y ago

Hm, an enum like `enum Color { R, O, Y, G, B, I, V }` is represented by a u8 at runtime (see for yourself here: http://is.gd/YkUY0l http://is.gd/YkUY0l), which means that you're only saving a single byte in your `Piece` struct by doing that manual optimization. What was the magnitude of the speedup that you saw?

Gankro 12y ago

There have been a few proposals for advanced bit-packing stuff, but most of it has been postponed as back-compat for later. That said, by default enum/struct layout is undefined, so it's possible the compiler could be taught to optimize your usecase correctly. For instance Option<&T> is the same size as &T because &T is strictly non-zero, and we can therefore use 0 for None.

kaoD 12y ago

Check kibwen's post (my sibling). It's [dead] for some reason but it answers your question. I'll reproduce it here: > Hm, an enum like `enum Color { R, O, Y, G, B, I, V }` is represented by a u8 at runtime (see for yourself here: http://is.gd/YkUY0l http://is.gd/YkUY0l), which means that you're only saving a single byte in your `Piece` struct by doing that manual optimization. What was the magnitude of the speedup that you saw?

nightpool 12y ago

FYI both kaoD and Kibwen's post seem to be dead because they included a link to a URL shortener (seems a little melodramatic on HNs part...) so I'll reproduce it here w/o the URL shortlink and see if that helps >Hm, an enum like `enum Color { R, O, Y, G, B, I, V }` is represented by a u8 at runtime (see for yourself here[1]), which means that you're only saving a single byte in your `Piece` struct by doing that manual optimization. What was the magnitude of the speedup that you saw? [1]: http://play.rust-lang.org/?code=%23%5Ballow(dead_code)%5D%0Aenum%20Color%20%7B%20R%2C%20O%2C%20Y%2C%20G%2C%20B%2C%20I%2C%20V%20%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20println!(%22%7B%7D%22%2C%20std%3A%3Amem%3A%3Asize_of%3A%3A%3CColor%3E())%3B%20%20%2F%2F%20size%20in%20bytes%0A%7D http://play.rust-lang.org/?code=%23%5Ballow(dead_code)%5D%0A...

iamdanfox 12y ago
Ah that's good to know, looks like I should switch it back! The manual u8 stuff was pretty marginal. (It was also before I discovered the `PartialEq` and `Copy` traits, so please forgive my Rust inexperience!)

deleted 12y ago

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