| # Bit-Slice Specialization |
| |
| This module provides specialized implementations for `BitSlice<T, Lsb0>` and |
| `BitSlice<T, Msb0>`. These implementations are able to use knowledge of their |
| bit-ordering behavior to be faster and operate in batches. |
| |
| Since true specialization is not available in the language yet, this uses the |
| `any::TypeId` system to detect if a type parameter is identical to a known type |
| and conditionally force a cast and branch. Since type identifiers are compiler |
| intrinsics produced during compilation, during monomorphization each branch |
| has its conditional replaced with a compile-time constant value. The `if true` |
| branch is retained, the `if false` branches are discarded, and the |
| monomorphization proceeds with the specialized function replacing the generic |
| body. |
| |
| The `.coerce()` and `.coerce_mut()` methods detect whether a bit-slice with |
| generic type parameters matches statically-known type parameters, and return an |
| `Option` of a value-identical bit-slice reference with the statically-known type |
| parameters which can then invoke a specialization method. |
| |
| Generic methods can be specialized whenever their implementation is dependent on |
| the `O` type parameter and the map of positions the ordering produces is |
| easily legible to processor instructions. Because language-level specialization |
| is unavailable, dispatch is only done in `bitvec` and cannot be extended to |
| third-party crates. |
| |
| The `lsb0` and `msb0` modules should have identical symbols present. For |
| implementation, remember that `Lsb0` and `Msb0` orderings **are** correlated |
| with little-endian and big-endian byte operations! |
