Program Listing for File ApplyIsingXX.hpp

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// Copyright 2018-2023 Xanadu Quantum Technologies Inc.

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at

//     http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#pragma once
#include "AVXUtil.hpp"
#include "BitUtil.hpp"
#include "Permutation.hpp"
#include "Util.hpp"

#include <complex>

namespace Pennylane::LightningQubit::Gates::AVXCommon {
template <typename PrecisionT, std::size_t packed_size> struct ApplyIsingXX {
    using Precision = PrecisionT;
    using PrecisionAVXConcept =
        typename AVXConcept<PrecisionT, packed_size>::Type;

    constexpr static std::size_t packed_size_ = packed_size;
    constexpr static bool symmetric = true;

    template <size_t rev_wire0, std::size_t rev_wire1>
    static consteval auto permutationInternalInternal() {
        std::array<uint8_t, packed_size> perm = {
            0,
        };

        std::size_t m = (1U << rev_wire0) | (1U << rev_wire1);
        for (size_t k = 0; k < packed_size / 2; k++) {
            perm[2 * k + 0] = 2 * (k ^ m) + 1;
            perm[2 * k + 1] = 2 * (k ^ m) + 0;
        }
        return Permutation::compilePermutation<PrecisionT>(perm);
    }

    template <size_t rev_wire0, std::size_t rev_wire1, class ParamT>
    static void applyInternalInternal(std::complex<PrecisionT> *arr,
                                      std::size_t num_qubits, bool inverse,
                                      ParamT angle) {
        const auto isin = inverse ? std::sin(angle / 2) : -std::sin(angle / 2);

        const auto real_cos =
            set1<PrecisionT, packed_size>(std::cos(angle / 2));
        const auto imag_sin = imagFactor<PrecisionT, packed_size>(isin);

        constexpr static auto perm =
            permutationInternalInternal<rev_wire0, rev_wire1>();
        PL_LOOP_PARALLEL(1)
        for (size_t n = 0; n < exp2(num_qubits); n += packed_size / 2) {
            const auto v = PrecisionAVXConcept::load(arr + n);

            const auto prod_cos = real_cos * v;
            const auto prod_sin = imag_sin * Permutation::permute<perm>(v);

            PrecisionAVXConcept::store(arr + n, prod_cos + prod_sin);
        }
    }
    template <size_t min_rev_wire, class ParamT>
    static void applyInternalExternal(std::complex<PrecisionT> *arr,
                                      std::size_t num_qubits,
                                      std::size_t max_rev_wire, bool inverse,
                                      ParamT angle) {
        using namespace Permutation;

        const std::size_t max_rev_wire_shift =
            (static_cast<std::size_t>(1U) << max_rev_wire);
        const std::size_t max_wire_parity = fillTrailingOnes(max_rev_wire);
        const std::size_t max_wire_parity_inv =
            fillLeadingOnes(max_rev_wire + 1);

        const auto isin = inverse ? std::sin(angle / 2) : -std::sin(angle / 2);
        const auto cos_factor =
            set1<PrecisionT, packed_size>(std::cos(angle / 2));
        const auto isin_factor = imagFactor<PrecisionT, packed_size>(isin);

        constexpr static auto perm = compilePermutation<PrecisionT>(
            swapRealImag(flip(identity<packed_size>(), min_rev_wire)));
        PL_LOOP_PARALLEL(1)
        for (size_t k = 0; k < exp2(num_qubits - 1); k += packed_size / 2) {
            const std::size_t i0 =
                ((k << 1U) & max_wire_parity_inv) | (max_wire_parity & k);
            const std::size_t i1 = i0 | max_rev_wire_shift;

            const auto v0 = PrecisionAVXConcept::load(arr + i0);
            const auto v1 = PrecisionAVXConcept::load(arr + i1);

            const auto prod_cos0 = cos_factor * v0;
            const auto prod_sin0 = isin_factor * Permutation::permute<perm>(v1);

            const auto prod_cos1 = cos_factor * v1;
            const auto prod_sin1 = isin_factor * Permutation::permute<perm>(v0);

            PrecisionAVXConcept::store(arr + i0, prod_cos0 + prod_sin0);
            PrecisionAVXConcept::store(arr + i1, prod_cos1 + prod_sin1);
        }
    }

    template <class ParamT>
    static void applyExternalExternal(std::complex<PrecisionT> *arr,
                                      const std::size_t num_qubits,
                                      const std::size_t rev_wire0,
                                      const std::size_t rev_wire1, bool inverse,
                                      ParamT angle) {
        using namespace Permutation;

        const std::size_t rev_wire0_shift = static_cast<std::size_t>(1U)
                                            << rev_wire0;
        const std::size_t rev_wire1_shift = static_cast<std::size_t>(1U)
                                            << rev_wire1;

        const std::size_t rev_wire_min = std::min(rev_wire0, rev_wire1);
        const std::size_t rev_wire_max = std::max(rev_wire0, rev_wire1);

        const std::size_t parity_low = fillTrailingOnes(rev_wire_min);
        const std::size_t parity_high = fillLeadingOnes(rev_wire_max + 1);
        const std::size_t parity_middle =
            fillLeadingOnes(rev_wire_min + 1) & fillTrailingOnes(rev_wire_max);

        const auto isin = inverse ? std::sin(angle / 2) : -std::sin(angle / 2);

        const auto cos_factor =
            set1<PrecisionT, packed_size>(std::cos(angle / 2));
        const auto isin_factor = imagFactor<PrecisionT, packed_size>(isin);

        constexpr static auto perm = compilePermutation<PrecisionT>(
            swapRealImag(identity<packed_size>()));
        PL_LOOP_PARALLEL(1)
        for (size_t k = 0; k < exp2(num_qubits - 2); k += packed_size / 2) {
            const std::size_t i00 = ((k << 2U) & parity_high) |
                                    ((k << 1U) & parity_middle) |
                                    (k & parity_low);
            const std::size_t i10 = i00 | rev_wire1_shift;
            const std::size_t i01 = i00 | rev_wire0_shift;
            const std::size_t i11 = i00 | rev_wire0_shift | rev_wire1_shift;

            const auto v00 = PrecisionAVXConcept::load(arr + i00); // 00
            const auto v01 = PrecisionAVXConcept::load(arr + i01); // 01
            const auto v10 = PrecisionAVXConcept::load(arr + i10); // 10
            const auto v11 = PrecisionAVXConcept::load(arr + i11); // 11

            const auto prod_cos00 = cos_factor * v00;
            const auto prod_isin00 = isin_factor * permute<perm>(v11);

            const auto prod_cos01 = cos_factor * v01;
            const auto prod_isin01 = isin_factor * permute<perm>(v10);

            const auto prod_cos10 = cos_factor * v10;
            const auto prod_isin10 = isin_factor * permute<perm>(v01);

            const auto prod_cos11 = cos_factor * v11;
            const auto prod_isin11 = isin_factor * permute<perm>(v00);

            PrecisionAVXConcept::store(arr + i00, prod_cos00 + prod_isin00);
            PrecisionAVXConcept::store(arr + i01, prod_cos01 + prod_isin01);
            PrecisionAVXConcept::store(arr + i10, prod_cos10 + prod_isin10);
            PrecisionAVXConcept::store(arr + i11, prod_cos11 + prod_isin11);
        }
    }
};
} // namespace Pennylane::LightningQubit::Gates::AVXCommon

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