/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2023 The Stockfish developers (see AUTHORS file)

  Stockfish is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Stockfish is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

// Constants used in NNUE evaluation function

#ifndef NNUE_COMMON_H_INCLUDED
#define NNUE_COMMON_H_INCLUDED

#include <cstring>
#include <iostream>

#include "../misc.h"  // for IsLittleEndian

#if defined(USE_AVX2)
#include <immintrin.h>

#elif defined(USE_SSE41)
#include <smmintrin.h>

#elif defined(USE_SSSE3)
#include <tmmintrin.h>

#elif defined(USE_SSE2)
#include <emmintrin.h>

#elif defined(USE_MMX)
#include <mmintrin.h>

#elif defined(USE_NEON)
#include <arm_neon.h>
#endif

namespace Stockfish::Eval::NNUE {

  // Version of the evaluation file
  constexpr std::uint32_t Version = 0x7AF32F20u;

  // Constant used in evaluation value calculation
  constexpr int OutputScale = 16;
  constexpr int WeightScaleBits = 6;

  // Size of cache line (in bytes)
  constexpr std::size_t CacheLineSize = 64;

  constexpr const char Leb128MagicString[] = "COMPRESSED_LEB128";
  constexpr const std::size_t Leb128MagicStringSize = sizeof(Leb128MagicString) - 1;

  // SIMD width (in bytes)
  #if defined(USE_AVX2)
  constexpr std::size_t SimdWidth = 32;

  #elif defined(USE_SSE2)
  constexpr std::size_t SimdWidth = 16;

  #elif defined(USE_MMX)
  constexpr std::size_t SimdWidth = 8;

  #elif defined(USE_NEON)
  constexpr std::size_t SimdWidth = 16;
  #endif

  constexpr std::size_t MaxSimdWidth = 32;

  // Type of input feature after conversion
  using TransformedFeatureType = std::uint8_t;
  using IndexType = std::uint32_t;

  // Round n up to be a multiple of base
  template <typename IntType>
  constexpr IntType ceil_to_multiple(IntType n, IntType base) {
      return (n + base - 1) / base * base;
  }

  // read_little_endian() is our utility to read an integer (signed or unsigned, any size)
  // from a stream in little-endian order. We swap the byte order after the read if
  // necessary to return a result with the byte ordering of the compiling machine.
  template <typename IntType>
  inline IntType read_little_endian(std::istream& stream) {
      IntType result;

      if (IsLittleEndian)
          stream.read(reinterpret_cast<char*>(&result), sizeof(IntType));
      else
      {
          std::uint8_t u[sizeof(IntType)];
          typename std::make_unsigned<IntType>::type v = 0;

          stream.read(reinterpret_cast<char*>(u), sizeof(IntType));
          for (std::size_t i = 0; i < sizeof(IntType); ++i)
              v = (v << 8) | u[sizeof(IntType) - i - 1];

          std::memcpy(&result, &v, sizeof(IntType));
      }

      return result;
  }

  // write_little_endian() is our utility to write an integer (signed or unsigned, any size)
  // to a stream in little-endian order. We swap the byte order before the write if
  // necessary to always write in little endian order, independently of the byte
  // ordering of the compiling machine.
  template <typename IntType>
  inline void write_little_endian(std::ostream& stream, IntType value) {

      if (IsLittleEndian)
          stream.write(reinterpret_cast<const char*>(&value), sizeof(IntType));
      else
      {
          std::uint8_t u[sizeof(IntType)];
          typename std::make_unsigned<IntType>::type v = value;

          std::size_t i = 0;
          // if constexpr to silence the warning about shift by 8
          if constexpr (sizeof(IntType) > 1)
          {
            for (; i + 1 < sizeof(IntType); ++i)
            {
                u[i] = (std::uint8_t)v;
                v >>= 8;
            }
          }
          u[i] = (std::uint8_t)v;

          stream.write(reinterpret_cast<char*>(u), sizeof(IntType));
      }
  }

  // read_little_endian(s, out, N) : read integers in bulk from a little indian stream.
  // This reads N integers from stream s and put them in array out.
  template <typename IntType>
  inline void read_little_endian(std::istream& stream, IntType* out, std::size_t count) {
      if (IsLittleEndian)
          stream.read(reinterpret_cast<char*>(out), sizeof(IntType) * count);
      else
          for (std::size_t i = 0; i < count; ++i)
              out[i] = read_little_endian<IntType>(stream);
  }

  // write_little_endian(s, values, N) : write integers in bulk to a little indian stream.
  // This takes N integers from array values and writes them on stream s.
  template <typename IntType>
  inline void write_little_endian(std::ostream& stream, const IntType* values, std::size_t count) {
      if (IsLittleEndian)
          stream.write(reinterpret_cast<const char*>(values), sizeof(IntType) * count);
      else
          for (std::size_t i = 0; i < count; ++i)
              write_little_endian<IntType>(stream, values[i]);
  }

  template <typename IntType>
  inline void read_leb_128(std::istream& stream, IntType* out, std::size_t count) {
      static_assert(std::is_signed_v<IntType>, "Not implemented for unsigned types");
      char leb128MagicString[Leb128MagicStringSize];
      stream.read(leb128MagicString, Leb128MagicStringSize);
      assert(strncmp(Leb128MagicString, leb128MagicString, Leb128MagicStringSize) == 0);
      const std::uint32_t BUF_SIZE = 4096;
      std::uint8_t buf[BUF_SIZE];
      auto bytes_left = read_little_endian<std::uint32_t>(stream);
      std::uint32_t buf_pos = BUF_SIZE;
      for (std::size_t i = 0; i < count; ++i) {
          IntType result = 0;
          size_t shift = 0;
          do {
              if (buf_pos == BUF_SIZE) {
                  stream.read(reinterpret_cast<char*>(buf), std::min(bytes_left, BUF_SIZE));
                  buf_pos = 0;
              }
              std::uint8_t byte = buf[buf_pos++];
              --bytes_left;
              result |= (byte & 0x7f) << shift;
              shift += 7;
              if ((byte & 0x80) == 0) {
                  out[i] = sizeof(IntType) * 8 <= shift || (byte & 0x40) == 0 ? result : result | ~((1 << shift) - 1);
                  break;
              }
          } while (shift < sizeof(IntType) * 8);
      }
      assert(bytes_left == 0);
  }

  template <typename IntType>
  inline void write_leb_128(std::ostream& stream, const IntType* values, std::size_t count) {
      static_assert(std::is_signed_v<IntType>, "Not implemented for unsigned types");
      stream.write(Leb128MagicString, Leb128MagicStringSize);
      std::uint32_t byte_count = 0;
      for (std::size_t i = 0; i < count; ++i) {
          IntType value = values[i];
          std::uint8_t byte;
          do {
              byte = value & 0x7f;
              value >>= 7;
              ++byte_count;
          } while ((byte & 0x40) == 0 ? value != 0 : value != -1);
      }
      write_little_endian(stream, byte_count);
      const std::uint32_t BUF_SIZE = 4096;
      std::uint8_t buf[BUF_SIZE];
      std::uint32_t buf_pos = 0;
      auto flush = [&]() {
          if (buf_pos > 0) {
              stream.write(reinterpret_cast<char*>(buf), buf_pos);
              buf_pos = 0;
          }
      };
      auto write = [&](std::uint8_t byte) {
          buf[buf_pos++] = byte;
          if (buf_pos == BUF_SIZE) flush();
      };
      for (std::size_t i = 0; i < count; ++i) {
          IntType value = values[i];
          while (true) {
              std::uint8_t byte = value & 0x7f;
              value >>= 7;
              if ((byte & 0x40) == 0 ? value == 0 : value == -1) {
                  write(byte);
                  break;
              }
              write(byte | 0x80);
          }
      }
      flush();
  }

}  // namespace Stockfish::Eval::NNUE

#endif // #ifndef NNUE_COMMON_H_INCLUDED
