// Copyright 2019 Google LLC. All Rights Reserved.
//
// 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
//
//     https://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.

#ifndef STATESPACE_AVX_H_
#define STATESPACE_AVX_H_

#include <immintrin.h>

#include <algorithm>
#include <cmath>
#include <complex>
#include <cstdint>
#include <functional>

#include "statespace.h"
#include "util.h"
#include "vectorspace.h"

namespace qsim {

namespace detail {

inline __m256i GetZeroMaskAVX(uint64_t i, uint64_t mask, uint64_t bits) {
  __m256i s1 = _mm256_setr_epi64x(i + 0, i + 2, i + 4, i + 6);
  __m256i s2 = _mm256_setr_epi64x(i + 1, i + 3, i + 5, i + 7);
  __m256i ma = _mm256_set1_epi64x(mask);
  __m256i bi = _mm256_set1_epi64x(bits);

  s1 = _mm256_and_si256(s1, ma);
  s2 = _mm256_and_si256(s2, ma);

  s1 = _mm256_cmpeq_epi64(s1, bi);
  s2 = _mm256_cmpeq_epi64(s2, bi);

  return _mm256_blend_epi32(s1, s2, 170);  // 10101010
}

inline double HorizontalSumAVX(__m256 s) {
  __m128 l = _mm256_castps256_ps128(s);
  __m128 h = _mm256_extractf128_ps(s, 1);
  __m128 s1  = _mm_add_ps(h, l);
  __m128 s1s = _mm_movehdup_ps(s1);
  __m128 s2 = _mm_add_ps(s1, s1s);

  return _mm_cvtss_f32(_mm_add_ss(s2, _mm_movehl_ps(s1s, s2)));
}

}  // namespace detail

/**
 * Object containing context and routines for AVX state-vector manipulations.
 * State is a vectorized sequence of eight real components followed by eight
 * imaginary components. Eight single-precison floating numbers can be loaded
 * into an AVX register.
 */
template <typename For>
class StateSpaceAVX :
    public StateSpace<StateSpaceAVX<For>, VectorSpace, For, float> {
 private:
  using Base = StateSpace<StateSpaceAVX<For>, qsim::VectorSpace, For, float>;

 public:
  using State = typename Base::State;
  using fp_type = typename Base::fp_type;

  template <typename... ForArgs>
  explicit StateSpaceAVX(ForArgs&&... args) : Base(args...) {}

  static uint64_t MinSize(unsigned num_qubits) {
    return std::max(uint64_t{16}, 2 * (uint64_t{1} << num_qubits));
  };

  void InternalToNormalOrder(State& state) const {
    if (state.num_qubits() == 1) {
      fp_type* s = state.get();

      s[2] = s[1];
      s[1] = s[8];
      s[3] = s[9];

      for (uint64_t i = 4; i < 16; ++i) {
        s[i] = 0;
      }
    } else if (state.num_qubits() == 2) {
      fp_type* s = state.get();

      s[6] = s[3];
      s[4] = s[2];
      s[2] = s[1];
      s[1] = s[8];
      s[3] = s[9];
      s[5] = s[10];
      s[7] = s[11];

      for (uint64_t i = 8; i < 16; ++i) {
        s[i] = 0;
      }
    } else {
      auto f = [](unsigned n, unsigned m, uint64_t i, fp_type* p) {
        fp_type* s = p + 16 * i;

        fp_type re[7];
        fp_type im[7];

        for (uint64_t i = 0; i < 7; ++i) {
          re[i] = s[i + 1];
          im[i] = s[i + 8];
        }

        for (uint64_t i = 0; i < 7; ++i) {
          s[2 * i + 1] = im[i];
          s[2 * i + 2] = re[i];
        }
      };

      Base::for_.Run(MinSize(state.num_qubits()) / 16, f, state.get());
    }
  }

  void NormalToInternalOrder(State& state) const {
    if (state.num_qubits() == 1) {
      fp_type* s = state.get();

      s[8] = s[1];
      s[1] = s[2];
      s[9] = s[3];

      for (uint64_t i = 2; i < 8; ++i) {
        s[i] = 0;
        s[i + 8] = 0;
      }
    } else if (state.num_qubits() == 2) {
      fp_type* s = state.get();

      s[8] = s[1];
      s[9] = s[3];
      s[10] = s[5];
      s[11] = s[7];
      s[1] = s[2];
      s[2] = s[4];
      s[3] = s[6];

      for (uint64_t i = 4; i < 8; ++i) {
        s[i] = 0;
        s[i + 8] = 0;
      }
    } else {
      auto f = [](unsigned n, unsigned m, uint64_t i, fp_type* p) {
        fp_type* s = p + 16 * i;

        fp_type re[7];
        fp_type im[7];

        for (uint64_t i = 0; i < 7; ++i) {
          im[i] = s[2 * i + 1];
          re[i] = s[2 * i + 2];
        }

        for (uint64_t i = 0; i < 7; ++i) {
          s[i + 1] = re[i];
          s[i + 8] = im[i];
        }
      };

      Base::for_.Run(MinSize(state.num_qubits()) / 16, f, state.get());
    }
  }

  void SetAllZeros(State& state) const {
    __m256 val0 = _mm256_setzero_ps();

    auto f = [](unsigned n, unsigned m, uint64_t i, __m256& val, fp_type* p) {
      _mm256_store_ps(p + 16 * i, val);
      _mm256_store_ps(p + 16 * i + 8, val);
    };

    Base::for_.Run(MinSize(state.num_qubits()) / 16, f, val0, state.get());
  }

  // Uniform superposition.
  void SetStateUniform(State& state) const {
    __m256 val0 = _mm256_setzero_ps();
    __m256 valu;

    fp_type v = double{1} / std::sqrt(uint64_t{1} << state.num_qubits());

    switch (state.num_qubits()) {
    case 1:
      valu = _mm256_set_ps(0, 0, 0, 0, 0, 0, v, v);
      break;
    case 2:
      valu = _mm256_set_ps(0, 0, 0, 0, v, v, v, v);
      break;
    default:
      valu = _mm256_set1_ps(v);
      break;
    }

    auto f = [](unsigned n, unsigned m, uint64_t i,
                __m256& val0, __m256 valu, fp_type* p) {
      _mm256_store_ps(p + 16 * i, valu);
      _mm256_store_ps(p + 16 * i + 8, val0);
    };

    Base::for_.Run(
        MinSize(state.num_qubits()) / 16, f, val0, valu, state.get());
  }

  // |0> state.
  void SetStateZero(State& state) const {
    SetAllZeros(state);
    state.get()[0] = 1;
  }

  static std::complex<fp_type> GetAmpl(const State& state, uint64_t i) {
    uint64_t k = (16 * (i / 8)) + (i % 8);
    return std::complex<fp_type>(state.get()[k], state.get()[k + 8]);
  }

  static void SetAmpl(
      State& state, uint64_t i, const std::complex<fp_type>& ampl) {
    uint64_t k = (16 * (i / 8)) + (i % 8);
    state.get()[k] = std::real(ampl);
    state.get()[k + 8] = std::imag(ampl);
  }

  static void SetAmpl(State& state, uint64_t i, fp_type re, fp_type im) {
    uint64_t k = (16 * (i / 8)) + (i % 8);
    state.get()[k] = re;
    state.get()[k + 8] = im;
  }

  // Sets state[i] = complex(re, im) where (i & mask) == bits.
  // if `exclude` is true then the criteria becomes (i & mask) != bits.
  void BulkSetAmpl(State& state, uint64_t mask, uint64_t bits,
                   const std::complex<fp_type>& val,
                   bool exclude = false) const {
    BulkSetAmpl(state, mask, bits, std::real(val), std::imag(val), exclude);
  }

  // Sets state[i] = complex(re, im) where (i & mask) == bits.
  // if `exclude` is true then the criteria becomes (i & mask) != bits.
  void BulkSetAmpl(State& state, uint64_t mask, uint64_t bits, fp_type re,
                   fp_type im, bool exclude = false) const {
    __m256 re_reg = _mm256_set1_ps(re);
    __m256 im_reg = _mm256_set1_ps(im);

    __m256i exclude_reg = _mm256_setzero_si256();
    if (exclude) {
      exclude_reg = _mm256_cmpeq_epi32(exclude_reg, exclude_reg);
    }

    auto f = [](unsigned n, unsigned m, uint64_t i, uint64_t maskv,
                uint64_t bitsv, __m256 re_n, __m256 im_n, __m256i exclude_n,
                fp_type* p) {
      __m256 ml = _mm256_castsi256_ps(_mm256_xor_si256(
          detail::GetZeroMaskAVX(8 * i, maskv, bitsv), exclude_n));

      __m256 re = _mm256_load_ps(p + 16 * i);
      __m256 im = _mm256_load_ps(p + 16 * i + 8);

      re = _mm256_blendv_ps(re, re_n, ml);
      im = _mm256_blendv_ps(im, im_n, ml);

      _mm256_store_ps(p + 16 * i, re);
      _mm256_store_ps(p + 16 * i + 8, im);
    };

    Base::for_.Run(MinSize(state.num_qubits()) / 16, f, mask, bits, re_reg,
                   im_reg, exclude_reg, state.get());
  }

  // Does the equivalent of dest += src elementwise.
  bool Add(const State& src, State& dest) const {
    if (src.num_qubits() != dest.num_qubits()) {
      return false;
    }

    auto f = [](unsigned n, unsigned m, uint64_t i,
                const fp_type* p1, fp_type* p2) {
      __m256 re1 = _mm256_load_ps(p1 + 16 * i);
      __m256 im1 = _mm256_load_ps(p1 + 16 * i + 8);
      __m256 re2 = _mm256_load_ps(p2 + 16 * i);
      __m256 im2 = _mm256_load_ps(p2 + 16 * i + 8);

      _mm256_store_ps(p2 + 16 * i, _mm256_add_ps(re1, re2));
      _mm256_store_ps(p2 + 16 * i + 8, _mm256_add_ps(im1, im2));
    };

    Base::for_.Run(MinSize(src.num_qubits()) / 16, f, src.get(), dest.get());

    return true;
  }

  // Does the equivalent of state *= a elementwise.
  void Multiply(fp_type a, State& state) const {
    __m256 r = _mm256_set1_ps(a);

    auto f = [](unsigned n, unsigned m, uint64_t i, __m256 r, fp_type* p) {
      __m256 re = _mm256_load_ps(p + 16 * i);
      __m256 im = _mm256_load_ps(p + 16 * i + 8);

      re = _mm256_mul_ps(re, r);
      im = _mm256_mul_ps(im, r);

      _mm256_store_ps(p + 16 * i, re);
      _mm256_store_ps(p + 16 * i + 8, im);
    };

    Base::for_.Run(MinSize(state.num_qubits()) / 16, f, r, state.get());
  }

  std::complex<double> InnerProduct(
      const State& state1, const State& state2) const {
    if (state1.num_qubits() != state2.num_qubits()) {
      return std::nan("");
    }

    auto f = [](unsigned n, unsigned m, uint64_t i,
                const fp_type* p1, const fp_type* p2) -> std::complex<double> {
      __m256 re1 = _mm256_load_ps(p1 + 16 * i);
      __m256 im1 = _mm256_load_ps(p1 + 16 * i + 8);
      __m256 re2 = _mm256_load_ps(p2 + 16 * i);
      __m256 im2 = _mm256_load_ps(p2 + 16 * i + 8);

      __m256 ip_re = _mm256_fmadd_ps(im1, im2, _mm256_mul_ps(re1, re2));
      __m256 ip_im = _mm256_fnmadd_ps(im1, re2, _mm256_mul_ps(re1, im2));

      double re = detail::HorizontalSumAVX(ip_re);
      double im = detail::HorizontalSumAVX(ip_im);

      return std::complex<double>{re, im};
    };

    using Op = std::plus<std::complex<double>>;
    return Base::for_.RunReduce(MinSize(state1.num_qubits()) / 16, f,
                                Op(), state1.get(), state2.get());
  }

  double RealInnerProduct(const State& state1, const State& state2) const {
    if (state1.num_qubits() != state2.num_qubits()) {
      return std::nan("");
    }

    auto f = [](unsigned n, unsigned m, uint64_t i,
                const fp_type* p1, const fp_type* p2) -> double {
      __m256 re1 = _mm256_load_ps(p1 + 16 * i);
      __m256 im1 = _mm256_load_ps(p1 + 16 * i + 8);
      __m256 re2 = _mm256_load_ps(p2 + 16 * i);
      __m256 im2 = _mm256_load_ps(p2 + 16 * i + 8);

      __m256 ip_re = _mm256_fmadd_ps(im1, im2, _mm256_mul_ps(re1, re2));

      return detail::HorizontalSumAVX(ip_re);
    };

    using Op = std::plus<double>;
    return Base::for_.RunReduce(MinSize(state1.num_qubits()) / 16, f,
                                Op(), state1.get(), state2.get());
  }

  template <typename DistrRealType = double>
  std::vector<uint64_t> Sample(
      const State& state, uint64_t num_samples, unsigned seed) const {
    std::vector<uint64_t> bitstrings;

    if (num_samples > 0) {
      double norm = 0;
      uint64_t size = MinSize(state.num_qubits()) / 16;
      const fp_type* p = state.get();

      for (uint64_t k = 0; k < size; ++k) {
        for (unsigned j = 0; j < 8; ++j) {
          double re = p[16 * k + j];
          double im = p[16 * k + 8 + j];
          norm += re * re + im * im;
        }
      }

      auto rs = GenerateRandomValues<DistrRealType>(num_samples, seed, norm);

      uint64_t m = 0;
      double csum = 0;
      bitstrings.reserve(num_samples);

      for (uint64_t k = 0; k < size; ++k) {
        for (unsigned j = 0; j < 8; ++j) {
          double re = p[16 * k + j];
          double im = p[16 * k + 8 + j];
          csum += re * re + im * im;
          while (rs[m] < csum && m < num_samples) {
            bitstrings.emplace_back(8 * k + j);
            ++m;
          }
        }
      }

      for (; m < num_samples; ++m) {
        bitstrings.emplace_back((uint64_t{1} << state.num_qubits()) - 1);
      }
    }

    return bitstrings;
  }

  using MeasurementResult = typename Base::MeasurementResult;

  void Collapse(const MeasurementResult& mr, State& state) const {
    auto f1 = [](unsigned n, unsigned m, uint64_t i,
                 uint64_t mask, uint64_t bits, const fp_type* p) -> double {
      __m256i ml = detail::GetZeroMaskAVX(8 * i, mask, bits);

      __m256 re = _mm256_maskload_ps(p + 16 * i, ml);
      __m256 im = _mm256_maskload_ps(p + 16 * i + 8, ml);
      __m256 s1 = _mm256_fmadd_ps(im, im, _mm256_mul_ps(re, re));

      return detail::HorizontalSumAVX(s1);
    };

    using Op = std::plus<double>;
    double norm = Base::for_.RunReduce(MinSize(state.num_qubits()) / 16, f1,
                                       Op(), mr.mask, mr.bits, state.get());

    __m256 renorm = _mm256_set1_ps(1.0 / std::sqrt(norm));

    auto f2 = [](unsigned n, unsigned m, uint64_t i,
                 uint64_t mask, uint64_t bits, __m256 renorm, fp_type* p) {
      __m256i ml = detail::GetZeroMaskAVX(8 * i, mask, bits);

      __m256 re = _mm256_maskload_ps(p + 16 * i, ml);
      __m256 im = _mm256_maskload_ps(p + 16 * i + 8, ml);

      re = _mm256_mul_ps(re, renorm);
      im = _mm256_mul_ps(im, renorm);

      _mm256_store_ps(p + 16 * i, re);
      _mm256_store_ps(p + 16 * i + 8, im);
    };

    Base::for_.Run(MinSize(state.num_qubits()) / 16, f2,
                   mr.mask, mr.bits, renorm, state.get());
  }

  std::vector<double> PartialNorms(const State& state) const {
    auto f = [](unsigned n, unsigned m, uint64_t i,
                const fp_type* p) -> double {
      __m256 re = _mm256_load_ps(p + 16 * i);
      __m256 im = _mm256_load_ps(p + 16 * i + 8);
      __m256 s1 = _mm256_fmadd_ps(im, im, _mm256_mul_ps(re, re));

      return detail::HorizontalSumAVX(s1);
    };

    using Op = std::plus<double>;
    return Base::for_.RunReduceP(
        MinSize(state.num_qubits()) / 16, f, Op(), state.get());
  }

  uint64_t FindMeasuredBits(
      unsigned m, double r, uint64_t mask, const State& state) const {
    double csum = 0;

    uint64_t k0 = Base::for_.GetIndex0(MinSize(state.num_qubits()) / 16, m);
    uint64_t k1 = Base::for_.GetIndex1(MinSize(state.num_qubits()) / 16, m);

    const fp_type* p = state.get();

    for (uint64_t k = k0; k < k1; ++k) {
      for (uint64_t j = 0; j < 8; ++j) {
        auto re = p[16 * k + j];
        auto im = p[16 * k + j + 8];
        csum += re * re + im * im;
        if (r < csum) {
          return (8 * k + j) & mask;
        }
      }
    }

    // Return the last bitstring in the unlikely case of underflow.
    return (8 * k1 - 1) & mask;
  }
};

}  // namespace qsim

#endif  // STATESPACE_AVX_H_
