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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,120 @@ | ||
| //! An SIMD shuffle implementation. | ||
| //! | ||
| //! Loosely based on Daniel Lemire's [SIMDxorshift]. | ||
| //! | ||
| //! [SIMDxorshift]: (https://github.com/lemire/SIMDxorshift | ||
| // use core::mem::size_of; | ||
| use stdsimd::simd::*; | ||
|
|
||
| // use distributions::range::SampleSingleHigh; | ||
| use distributions::uniform::WideningMultiply; | ||
| use {swap_unchecked, Rng}; | ||
|
|
||
| /// A trait for shuffling slices. | ||
| pub trait SimdShuf { | ||
| /// Shuffle a mutable slice in place, using an SIMD implementation. | ||
| /// | ||
| /// To be used in the form: | ||
| /// ```rust | ||
| /// u16x8::simd_shuffle(&mut rng, &mut list); | ||
| /// ``` | ||
| /// | ||
| /// Use a vector of size greater than or equal to the PRNG output. | ||
| /// Smaller lane widths will likely be faster for equal vector sizes. | ||
| /// | ||
| /// # Panics | ||
| /// | ||
| /// If `values.len()` is larger than the maximum value of the vector's | ||
| /// lanes. (If `values.len()` is unknown, use a `u32xN` or `u64xN` | ||
| /// vector depending on [`target_pointer_width`].) | ||
| /// | ||
| /// [`target_pointer_width`]: https://doc.rust-lang.org/reference/attributes.html#conditional-compilation | ||
| fn simd_shuffle<R: Rng, T>(rng: &mut R, values: &mut [T]); | ||
| } | ||
|
|
||
| macro_rules! impl_simd_shuf { | ||
| ($vec:ident, $scalar:ident) => { | ||
| impl SimdShuf for $vec { | ||
| // TODO: make this adapt when too many/few elements | ||
| // could match on values.len and use an appropriate | ||
| // lane width, based on chosen vector width | ||
| #[inline(always)] | ||
| fn simd_shuffle<R: Rng, T>(rng: &mut R, values: &mut [T]) { | ||
| assert!( | ||
| values.len() <= $scalar::max_value() as usize, | ||
| "Slice length too long for the vector's lanes", | ||
| ); | ||
|
|
||
| // Create a vector to hold `$vec::lanes()` range bounds at | ||
| // once. This should be evaluated at compile-time. | ||
| // TODO: consider making this a macro | ||
| let mut interval = $vec::default(); | ||
| for vec_idx in 0..$vec::lanes() { | ||
| // (len, len - 1, len - 2, len - 3, ..., len - $vec::lanes() + 1) | ||
| interval = interval.replace(vec_idx, (values.len() - vec_idx) as $scalar); | ||
| } | ||
| let mut slice_idx = values.len(); | ||
|
|
||
| // shuffle a multiple of `$vec::lanes()` slice elements | ||
| for _ in 0..values.len() / $vec::lanes() { | ||
| let rand_indices = rng.gen_range($vec::splat(0), interval); | ||
|
|
||
| // swap each `rand_idx` with the next `slice_idx` | ||
| // TODO: could probably be optimized | ||
| for vec_idx in 0..$vec::lanes() { | ||
| slice_idx -= 1; | ||
| let rand_idx = rand_indices.extract(vec_idx) as usize; | ||
| unsafe { swap_unchecked(values, slice_idx, rand_idx); } | ||
| } | ||
|
|
||
| // move onto the next interval | ||
| interval -= $vec::lanes() as $scalar; | ||
| } | ||
|
|
||
| // shuffle the remaining elements | ||
| // This is likely overzealous | ||
| let remainder = values.len() % $vec::lanes(); | ||
| if remainder > 1 { | ||
| match remainder - 1 { | ||
| 1...2 => rem_shuf!(u16x2, remainder, rng, values, slice_idx, u16), | ||
| 3...4 => rem_shuf!(u16x4, remainder, rng, values, slice_idx, u16), | ||
| 5...8 => rem_shuf!(u16x8, remainder, rng, values, slice_idx, u16), | ||
| 9...16 => rem_shuf!(u16x16, remainder, rng, values, slice_idx, u16), | ||
| 17...32 => rem_shuf!(u16x32, remainder, rng, values, slice_idx, u16), | ||
| 33...64 | _ => rem_shuf!(u8x64, remainder, rng, values, slice_idx, u8), | ||
| } | ||
| } | ||
| } | ||
| } | ||
| }; | ||
|
|
||
| // bulk implementation for scalar types | ||
| ($($vec:ident,)+, $scalar:ident) => {$( | ||
| impl_simd_shuf!($vec, $scalar); | ||
| )+}; | ||
| } | ||
|
|
||
| macro_rules! rem_shuf { | ||
| ($vec:ident, $rem:ident, $rng:ident, $values:ident, $slice_idx:ident, $scalar:ty) => {{ | ||
| // We can exit interval generation early, because we only need a few | ||
| // indices. We can't avoid generating unneeded random indices however, | ||
| // so we use a default value of 1 to speed up the uniform sampling. | ||
| let mut interval = $vec::splat(1); | ||
| for vec_idx in 0..$rem - 1 { | ||
| interval = interval.replace(vec_idx, ($rem - vec_idx) as $scalar); | ||
| } | ||
|
|
||
| let rand_indices = $rng.gen_range($vec::splat(0), interval); | ||
| for vec_idx in 0..$rem - 1 { | ||
| $slice_idx -= 1; | ||
| let rand_idx = rand_indices.extract(vec_idx) as usize; | ||
| unsafe { swap_unchecked($values, $slice_idx, rand_idx); } | ||
| } | ||
| }}; | ||
| } | ||
|
|
||
| impl_simd_shuf!(u8x2, u8x4, u8x8, u8x16, u8x32, u8x64,, u8); | ||
| impl_simd_shuf!(u16x2, u16x4, u16x8, u16x16, u16x32,, u16); | ||
| impl_simd_shuf!(u32x2, u32x4, u32x8, u32x16,, u32); | ||
| impl_simd_shuf!(u64x2, u64x4, u64x8,, u64); |