On 2 October 2012 23:52, jerro <a...@a.com> wrote: > On Tuesday, 2 October 2012 at 13:36:37 UTC, Manu wrote: > >> On 2 October 2012 13:49, jerro <a...@a.com> wrote: >> >> >>> I don't think it is possible to think of all usages of this, but for >>> every >>> simd instruction there are valid usages. At least for writing pfft, I >>> found >>> shuffling two vectors very useful. For, example, I needed a function that >>> takes a small, square, power of two number of elements stored in vectors >>> and bit-reverses them - it rearanges them so that you can calculate the >>> new >>> index of each element by reversing bits of the old index (for 16 elements >>> using 4 element vectors this can actually be done using >>> std.simd.transpose, >>> but for AVX it was more efficient to make this function work on 64 >>> elements). There are other places in pfft where I need to select elements >>> from two vectors (for example, here >>> https://github.com/jerro/pfft/****<https://github.com/jerro/pfft/**> >>> blob/sine-transform/pfft/avx_****float.d#L141<https://github.** >>> com/jerro/pfft/blob/sine-**transform/pfft/avx_float.d#**L141<https://github.com/jerro/pfft/blob/sine-transform/pfft/avx_float.d#L141>>is >>> the platform specific code for AVX). >>> >>> >>> I don't think this are the kind of things that should be implemented in >>> std.simd. If you wanted to implement all such operations (for example bit >>> reversing a small array) that somebody may find useful at some time, >>> std.simd would need to be huge, and most of it would never be used. >>> >> >> >> I was referring purely to your 2-vector swizzle idea (or useful high-level >> ideas in general). Not to hyper-context-specific functions :P >> > > My point was that those context specific functions can be implemented > using a 2 vector swizzle. LLVM, for example, actually provides access to > most vector shuffling instruction through "shufflevector", which is > basically a 2 vector swizzle. >
Yeah, I understand. And it's a good suggestion. I'll add support for 2-vector swizzling next time I'm working on it.
