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mlx/mlx/backend/cuda/iterators/general_iterator.cuh
2025-06-09 06:45:08 -07:00

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// Copyright © 2025 Apple Inc.
#pragma once
#include <thrust/iterator/iterator_adaptor.h>
#include <cuda/std/utility>
#include "mlx/backend/cuda/kernel_utils.cuh"
namespace mlx::core::cu {
// Iterating non-contiguous array.
template <typename Iterator, typename IdxT = int64_t>
class general_iterator
: public thrust::
iterator_adaptor<general_iterator<Iterator, IdxT>, Iterator> {
public:
using super_t =
thrust::iterator_adaptor<general_iterator<Iterator, IdxT>, Iterator>;
using reference = typename super_t::reference;
using difference_type = typename super_t::difference_type;
__host__ __device__ general_iterator(
Iterator it,
IdxT index,
int ndim,
Shape shape,
Strides strides)
: super_t(it),
index_(index),
ndim_(ndim),
shape_(cuda::std::move(shape)),
strides_(cuda::std::move(strides)) {}
__host__ __device__ IdxT index() const {
return index_;
}
__host__ __device__ const Shape& shape() const {
return shape_;
}
__host__ __device__ const Strides& strides() const {
return strides_;
}
private:
friend class thrust::iterator_core_access;
__host__ __device__ bool equal(const general_iterator& other) const {
return this->base() == other.base() && this->index() == other.index();
}
__host__ __device__ void advance(difference_type n) {
this->index_ += n;
}
__host__ __device__ void increment() {
this->index_ += 1;
}
__host__ __device__ void decrement() {
this->index_ -= 1;
}
__host__ __device__ difference_type
distance_to(const general_iterator& other) const {
_CCCL_ASSERT(
this->base() == other.base(),
"Underlying iterator must point to same base iterator");
return other.index() - this->index();
}
// The dereference is device-only to avoid accidental running in host.
__device__ typename super_t::reference dereference() const {
IdxT offset = elem_to_loc(index_, shape_.data(), strides_.data(), ndim_);
return *(this->base() + offset);
}
IdxT index_;
int ndim_;
Shape shape_;
Strides strides_;
};
template <typename IdxT, typename Iterator>
__host__ __device__ auto make_general_iterator(
Iterator it,
IdxT index,
int ndim,
Shape shape,
Strides strides) {
return general_iterator<Iterator, IdxT>(
it, index, ndim, cuda::std::move(shape), cuda::std::move(strides));
}
template <typename IdxT, typename Iterator>
auto make_general_iterator(
Iterator it,
const std::vector<int32_t>& shape,
const std::vector<int64_t>& strides) {
return make_general_iterator<IdxT>(
it, 0, shape.size(), const_param(shape), const_param(strides));
}
template <typename IdxT, typename Iterator>
auto make_general_iterators(
Iterator it,
IdxT size,
const std::vector<int32_t>& shape,
const std::vector<int64_t>& strides) {
auto ndim = shape.size();
auto shape_arg = const_param(shape);
auto strides_arg = const_param(strides);
return std::make_pair(
make_general_iterator<IdxT>(it, 0, ndim, shape_arg, strides_arg),
make_general_iterator<IdxT>(it, size, ndim, shape_arg, strides_arg));
}
} // namespace mlx::core::cu