// Copyright (c) 2019 Graphcore Ltd. All rights reserved.
#include "RandomUtils.hpp"

using namespace poplar;

namespace poprand {

template <typename OutType> class Uniform : public MultiVertex {
public:
  Uniform();

  Output<Vector<OutType, SPAN, 8>> out;
  const float offset;
  const float scale;

  IS_EXTERNAL_CODELET(true);

  void compute(unsigned wid) {
    if (wid == 0) {
      uint32_t seed[2] = {0xDEADBEEF, 0xBEEFDEAD};
      uint32_t seedModifier = 0x900DDEED;

      uint64_t seedH = seed[0] + (static_cast<uint64_t>(seed[1]) << 32);
      uint64_t seedL = seed[1] + (static_cast<uint64_t>(seed[0]) << 32);
      auto s = initialiseAndPrime({seedL, seedH});
      bool isHalf = std::is_same<OutType, half>::value;
      const unsigned maxPerCall = isHalf ? 4 : 2;
      const unsigned bitsPerVal = isHalf ? 16 : 32;

      unsigned n = out.size();
      unsigned idx = 0;
      while (n) {
        const unsigned genSamples = min(n, maxPerCall);
        auto r = next(s);
        for (auto k = 0; k != genSamples; ++k, ++idx, r >>= bitsPerVal) {
          out[idx] =
              static_cast<float>(convertToUniform<OutType>(r)) * scale + offset;
        }
        n -= genSamples;
      }
    }
  }
};

template class Uniform<float>;
template class Uniform<half>;

// Template specialisation for int
template <> class Uniform<int> : public MultiVertex {
public:
  Uniform();

  Output<Vector<int, SPAN, 8>> out;
  const int offset;
  // is the range of the uniform generator. Called scale because it can also
  // be seen as a scale factor for an uniform distribution [0,1) to produce the
  // integer
  const uint32_t scale;

  IS_EXTERNAL_CODELET(true);

  void compute(unsigned wid) {
    if (wid == 0) {
      uint32_t seed[2] = {0xDEADBEEF, 0xBEEFDEAD};
      uint32_t seedModifier = 0x900DDEED;

      uint64_t seedH = seed[0] + (static_cast<uint64_t>(seed[1]) << 32);
      uint64_t seedL = seed[1] + (static_cast<uint64_t>(seed[0]) << 32);
      auto s = initialiseAndPrime({seedL, seedH});
      const unsigned maxPerCall = 2;
      const unsigned bitsPerVal = 32;
      unsigned n = out.size();
      unsigned idx = 0;
      const uint64_t scale64Bit = scale;
      while (n) {
        const unsigned genSamples = min(n, maxPerCall);
        auto r = next(s);
        for (auto k = 0; k != genSamples; ++k, ++idx, r >>= bitsPerVal) {
          uint64_t rmasked = r & ((1ULL << bitsPerVal) - 1);
          // scale == 0 is the special case where whole range of int is used
          if (scale != 0) {
            rmasked = (scale64Bit * rmasked) >> bitsPerVal;
          }
          int64_t res32 = static_cast<int64_t>(rmasked) + offset;
          out[idx] = res32;
        }
        n -= genSamples;
      }
    }
  }
};

} // namespace poprand