Working through giving example documentation to every Simd function.
The major change in this patch is using doc macros to generate
type-specific examples for each function, using a visually-apparent type
constructor. This makes it feel nicer to have twelve separate
documentation entries for reduce_product(), for example.
A simpler variant of rust-lang/portable-simd#206.
* Comparisons are moved to `SimdPartialEq`, `SimdPartialOrd`, and `SimdOrd`. The function names are prefixed with `simd_` to disambiguate from the regular `PartialEq` etc functions. With the functions on traits instead of `Simd` directly, shadowing the function names doesn't work very well.
* Floating point `Ord`-like functions are put into a `SimdFloat` trait. The intention is that eventually (some time after this PR) all floating point functions will be moved from `Simd` to `SimdFloat`, and the same goes for future `SimdInt`/`SimdUint` traits.
Now that we are thoroughly embedded in libcore, we don't need these on by default.
Indeed, their presence may provide confusing results during integration attempts.
Another approach that fixesrust-lang/portable-simd#223, as an alternative to rust-lang/portable-simd#238.
This adds the `ToBitMask` trait, which is implemented on a vector for each bitmask type it supports. This includes all unsigned integers with enough bits to contain it. The byte array variant has been separated out for now into rust-lang/portable-simd#246 and still requires `generic_const_exprs`, but the integer variants no longer require it and can make it to nightly.
* Explain unsafe contracts of core::simd
This permeates the module with remarks on safety for pub methods,
layout of the Simd type, correct use of intrinsics, et cetera.
This is mostly to help others curious about how core::simd works,
including other Rust contributors, `unsafe` library authors,
and eventually ourselves.
