This supports swizzling? If so, *very* cool (I've wanted swizzling in
Rust for some time).
J
On 07/15/2013 09:27 PM, Jens Nockert wrote:
Hello rust-dev!
I implemented OpenCL-style[0] accessors for SIMD types in Rust[1], the code
quality isn't near /merge-worthy yet, but I wanted some input.
For some code-examples, go to
https://github.com/jensnockert/rust/tree/simd/src/test/run-pass/simd-test and
check it out, you should be able to get the idea of how they work.
Note that I didn't add any actual syntax for vector types yet (since it would be
highly controversial and I don't know what would be the best option), so I just added
a simd!(name: T * n) syntax extension that declares a new type that maps down to a
LLVM <n * T>.
My preference for syntax right now would be simd!(n x T) if I can get that to
parse, or simd!(T, ..n). And then you would declare a type with type f32x4 =
simd(4 x f32); and it would magically work. Another option would be some
variant of the [T, ..n] syntax used for fixed-length vectors.
Introducing a new t, ty_simd_vec(t, uint), instead of using the current #[simd]
struct { … }, is yet another thing that is controversial about the patch and
this needs a bit of explanation of the problem with #[simd] struct { … }.
To be able to make these accessors work, you unfortunately need to be able to
generate anonymous types in the compiler, x.even for example (take the
even-indexed elements of a vector) may be a type that is undeclared. And if you
want to be able to pretty-print that, you need to be able to generate a type
without a name, which makes #[simd] struct { … } impossible.
You could just pre-declare all possible options up to 256-bit long, which
probably would only be a hundred types or so, but would feel a bit silly.
There are also other operations that could generate (possibly) unnamed types,
like a == b, which should generate a i1-vector, or a shufflevector intrinsic
that could generate vectors of any length.
Ps. I didn't think of #[simd] (T, T, T, T) &c. before implementing (sanxiyn
gave me that idea), but I still think that is probably a worse idea than adding
SIMD as an additional type with actual syntax.
[0]: http://www.khronos.org/files/opencl-quick-reference-card.pdf, page 2, "Vector
Component Addressing"
[1]: https://github.com/jensnockert/rust/tree/simd
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