compression.cc

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#include "compression.h"
 
#include <climits>
#include <iostream>
#include <memory>
#include <string>
 
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/str_format.h"
#include "rom/rom.h"
#include "util/hyrule_magic.h"
#include "util/macro.h"
 
#define DEBUG_LOG(msg) std::cout << msg << std::endl
 
namespace yaze {
namespace gfx {
 
std::vector<uint8_t> HyruleMagicCompress(uint8_t const* const src,
                                         int const oldsize, int* const size,
                                         int const flag) {
  // Allocate buffer large enough for worst-case output
  std::vector<uint8_t> b2(std::max(0x1000, oldsize * 2));
 
  int i, j, k, l, m = 0, n, o = 0, bd = 0, p, q = 0, r;
 
  for (i = 0; i < oldsize;) {
    l = src[i];  // grab a char from the buffer.
 
    k = 0;
 
    r = !!q;  // r = the same logical value (0 or 1) as q, but not the same
              // value necesarily.
 
    for (j = 0; j < i - 1; j++) {
      if (src[j] == l) {
        m = oldsize - j;
 
        for (n = 0; n < m; n++)
          if (src[n + j] != src[n + i])
            break;
 
        if (n > k)
          k = n, o = j;
      }
    }
 
    for (n = i + 1; n < oldsize; n++) {
      if (src[n] != l) {
        break;
      }
    }
 
    n -= i;  // offset back by i. i.e. n = k+1 as above.
 
    if (n > 1 + r)
      p = 1;
    else {
      m = src[i + 1];
 
      for (n = i + 2; n < oldsize; n++) {
        if (src[n] != l)
          break;
 
        n++;
 
        if (src[n] != m)
          break;
      }
 
      n -= i;
 
      if (n > 2 + r)
        p = 2;
      else {
        m = oldsize - i;
 
        for (n = 1; n < m; n++)
          if (src[i + n] != l + n)
            break;
 
        if (n > 1 + r)
          p = 3;
        else
          p = 0;
      }
    }
 
    if (k > 3 + r && k > n + (p & 1))
      p = 4, n = k;
 
    if (!p)
      q++, i++;
    else {
      if (q) {
        q--;
 
        if (q > 31) {
          b2[bd++] = (unsigned char)(224 + (q >> 8));
        }
 
        b2[bd++] = (unsigned char)q;
        q++;
 
        memcpy(b2.data() + bd, src + i - q, q);
 
        bd += q;
        q = 0;
      }
 
      i += n;
      n--;
 
      if (n > 31) {
        b2[bd++] = (unsigned char)(224 + (n >> 8) + (p << 2));
        b2[bd++] = (unsigned char)n;
      } else
        b2[bd++] = (unsigned char)((p << 5) + n);
 
      switch (p) {
        case 1:
        case 3:
          b2[bd++] = (unsigned char)l;
          break;
 
        case 2:
          b2[bd++] = (unsigned char)l;
          b2[bd++] = (unsigned char)m;
 
          break;
 
        case 4:
          if (flag) {
            b2[bd++] = (unsigned char)(o >> 8);
            b2[bd++] = (unsigned char)o;
          } else {
            b2[bd++] = (unsigned char)o;
            b2[bd++] = (unsigned char)(o >> 8);
          }
      }
 
      continue;
    }
  }
 
  if (q) {
    q--;
 
    if (q > 31) {
      b2[bd++] = (unsigned char)(224 + (q >> 8));
    }
 
    b2[bd++] = (unsigned char)q;
    q++;
 
    memcpy(b2.data() + bd, src + i - q, q);
 
    bd += q;
  }
 
  b2[bd++] = 255;
  b2.resize(bd);
  *size = bd;
 
  return b2;
}
 
std::vector<uint8_t> HyruleMagicDecompress(uint8_t const* src, int* const size,
                                           int const p_big_endian,
                                           size_t max_src_size) {
  std::vector<uint8_t> b2(1024);
  const uint8_t* const src_start = src;
 
  int bd = 0, bs = 1024;
 
  unsigned char a;
  unsigned char b;
  unsigned short c, d;
 
  // Use a lambda to allow early returns instead of goto end_decompression
  auto decompress_loop = [&]() {
    for (;;) {
      // Bounds check: Ensure we can read at least one byte (command)
      if (max_src_size != static_cast<size_t>(-1) &&
          (size_t)(src - src_start) >= max_src_size) {
        std::cerr
            << "HyruleMagicDecompress: Reached end of buffer unexpectedly."
            << std::endl;
        return;
      }
 
      // retrieve a uint8_t from the buffer.
      a = *(src++);
 
      // end the decompression routine if we encounter 0xff.
      if (a == 0xff)
        return;
 
      // examine the top 3 bits of a.
      b = (a >> 5);
 
      if (b == 7)  // i.e. 0b 111
      {
        // get bits 0b 0001 1100
        b = ((a >> 2) & 7);
 
        // get bits 0b 0000 0011, multiply by 256, OR with the next byte.
        c = ((a & 0x0003) << 8);
 
        // Bounds check: Ensure we can read the next byte
        if (max_src_size != static_cast<size_t>(-1) &&
            (size_t)(src - src_start) >= max_src_size) {
          std::cerr << "HyruleMagicDecompress: Reached end of buffer reading "
                       "extended len"
                    << std::endl;
          return;
        }
        c |= *(src++);
      } else
        // or get bits 0b 0001 1111
        c = (uint16_t)(a & 31);
 
      c++;
 
      if ((bd + c) > (bs - 512)) {
        // need to increase the buffer size.
        bs += 1024;
        // Safety check for excessive allocation
        if (bs > 1024 * 1024 * 16) {  // 16MB limit
          std::cerr << "HyruleMagicDecompress: Excessive allocation detected."
                    << std::endl;
          bd = 0;
          return;
        }
        b2.resize(bs);
      }
 
      // 7 was handled, here we handle other decompression codes.
 
      switch (b) {
        case 0:  // 0b 000
 
          // raw copy
 
          // Bounds check: Ensure we can read c bytes
          if (max_src_size != static_cast<size_t>(-1) &&
              (size_t)(src - src_start + c) > max_src_size) {
            std::cerr << "HyruleMagicDecompress: Raw copy exceeds buffer."
                      << std::endl;
            return;
          }
 
          // copy info from the src buffer to our new buffer
          memcpy(b2.data() + bd, src, c);
 
          // increment the src pointer accordingly.
          src += c;
 
          bd += c;
 
          break;
 
        case 1:  // 0b 001
 
          // rle copy
 
          // Bounds check: Ensure we can read 1 byte
          if (max_src_size != static_cast<size_t>(-1) &&
              (size_t)(src - src_start) >= max_src_size) {
            std::cerr << "HyruleMagicDecompress: RLE copy exceeds buffer."
                      << std::endl;
            return;
          }
 
          // make c duplicates of one byte, inc the src pointer.
          memset(b2.data() + bd, *(src++), c);
 
          // increase the b2 offset.
          bd += c;
 
          break;
 
        case 2:  // 0b 010
 
          // rle 16-bit alternating copy
 
          // Bounds check: Ensure we can read 2 bytes
          if (max_src_size != static_cast<size_t>(-1) &&
              (size_t)(src - src_start + 2) > max_src_size) {
            std::cerr
                << "HyruleMagicDecompress: RLE 16-bit copy exceeds buffer."
                << std::endl;
            return;
          }
 
          d = zelda3::ldle16b(src);
 
          src += 2;
 
          while (c > 1) {
            // copy that 16-bit number c/2 times into the b2 buffer.
            zelda3::stle16b(b2.data() + bd, d);
 
            bd += 2;
            c -= 2;  // hence c/2
          }
 
          if (c)  // if there's a remainder of c/2, this handles it.
            b2[bd++] = (char)d;
 
          break;
 
        case 3:  // 0b 011
 
          // incrementing copy
 
          // Bounds check: Ensure we can read 1 byte
          if (max_src_size != static_cast<size_t>(-1) &&
              (size_t)(src - src_start) >= max_src_size) {
            std::cerr << "HyruleMagicDecompress: Inc copy exceeds buffer."
                      << std::endl;
            return;
          }
 
          // get the current src byte.
          a = *(src++);
 
          while (c--) {
            b2[bd++] = a++;
          }
 
          break;
 
        default:  // 0b 100, 101, 110
 
          // lz copy
 
          // Bounds check: Ensure we can read 2 bytes
          if (max_src_size != static_cast<size_t>(-1) &&
              (size_t)(src - src_start + 2) > max_src_size) {
            std::cerr << "HyruleMagicDecompress: LZ copy exceeds buffer."
                      << std::endl;
            return;
          }
 
          if (p_big_endian) {
            d = (*src << 8) + src[1];
          } else {
            d = zelda3::ldle16b(src);
          }
 
          while (c--) {
            if (d >= static_cast<unsigned short>(bs)) {
              std::cerr << "HyruleMagicDecompress: LZ ref out of bounds."
                        << std::endl;
              return;
            }
            b2[bd++] = b2[d++];
          }
 
          src += 2;
      }
    }
  };
 
  decompress_loop();
 
  b2.resize(bd);
 
  if (size)
    (*size) = bd;
 
  return b2;
}
 
namespace lc_lz2 {
 
void PrintCompressionPiece(const CompressionPiecePointer& piece) {
  std::cout << "Command: " << std::to_string(piece->command) << "\n";
  std::cout << "Command Length: " << piece->length << "\n";
  std::cout << "Argument: ";
  auto arg_size = piece->argument.size();
  for (int i = 0; i < arg_size; ++i) {
    printf("%02X ", piece->argument.at(i));
  }
  std::cout << "\nArgument Length: " << piece->argument_length << "\n";
}
 
void PrintCompressionChain(const CompressionPiecePointer& chain_head) {
  auto compressed_chain = chain_head->next;
  while (compressed_chain != nullptr) {
    std::cout << "- Compression Piece -\n";
    PrintCompressionPiece(compressed_chain);
    compressed_chain = compressed_chain->next;
  }
}
 
void CheckByteRepeat(const uint8_t* rom_data, DataSizeArray& data_size_taken,
                     CommandArgumentArray& cmd_args, uint& src_data_pos,
                     const unsigned int last_pos) {
  unsigned int pos = src_data_pos;
  char byte_to_repeat = rom_data[pos];
  while (pos <= last_pos && rom_data[pos] == byte_to_repeat) {
    data_size_taken[kCommandByteFill]++;
    pos++;
  }
  cmd_args[kCommandByteFill][0] = byte_to_repeat;
}
 
void CheckWordRepeat(const uint8_t* rom_data, DataSizeArray& data_size_taken,
                     CommandArgumentArray& cmd_args, uint& src_data_pos,
                     const unsigned int last_pos) {
  if (src_data_pos + 2 <= last_pos &&
      rom_data[src_data_pos] != rom_data[src_data_pos + 1]) {
    unsigned int pos = src_data_pos;
    char byte1 = rom_data[pos];
    char byte2 = rom_data[pos + 1];
    pos += 2;
    data_size_taken[kCommandWordFill] = 2;
    while (pos + 1 <= last_pos) {
      if (rom_data[pos] == byte1 && rom_data[pos + 1] == byte2)
        data_size_taken[kCommandWordFill] += 2;
      else
        break;
      pos += 2;
    }
    cmd_args[kCommandWordFill][0] = byte1;
    cmd_args[kCommandWordFill][1] = byte2;
  }
}
 
void CheckIncByte(const uint8_t* rom_data, DataSizeArray& data_size_taken,
                  CommandArgumentArray& cmd_args, uint& src_data_pos,
                  const unsigned int last_pos) {
  unsigned int pos = src_data_pos;
  char byte = rom_data[pos];
  pos++;
  data_size_taken[kCommandIncreasingFill] = 1;
  byte++;
  while (pos <= last_pos && byte == rom_data[pos]) {
    data_size_taken[kCommandIncreasingFill]++;
    byte++;
    pos++;
  }
  cmd_args[kCommandIncreasingFill][0] = rom_data[src_data_pos];
}
 
void CheckIntraCopy(const uint8_t* rom_data, DataSizeArray& data_size_taken,
                    CommandArgumentArray& cmd_args, uint& src_data_pos,
                    const unsigned int last_pos, unsigned int start) {
  if (src_data_pos != start) {
    unsigned int searching_pos = start;
    unsigned int current_pos_u = src_data_pos;
    unsigned int copied_size = 0;
    unsigned int search_start = start;
 
    while (searching_pos < src_data_pos && current_pos_u <= last_pos) {
      while (rom_data[current_pos_u] != rom_data[searching_pos] &&
             searching_pos < src_data_pos)
        searching_pos++;
      search_start = searching_pos;
      while (current_pos_u <= last_pos &&
             rom_data[current_pos_u] == rom_data[searching_pos] &&
             searching_pos < src_data_pos) {
        copied_size++;
        current_pos_u++;
        searching_pos++;
      }
      if (copied_size > data_size_taken[kCommandRepeatingBytes]) {
        search_start -= start;
        printf("- Found repeat of %d at %d\n", copied_size, search_start);
        data_size_taken[kCommandRepeatingBytes] = copied_size;
        cmd_args[kCommandRepeatingBytes][0] = search_start & kSnesByteMax;
        cmd_args[kCommandRepeatingBytes][1] = search_start >> 8;
      }
      current_pos_u = src_data_pos;
      copied_size = 0;
    }
  }
}
 
// Check if a command managed to pick up `max_win` or more bytes
// Avoids being even with copy command, since it's possible to merge copy
void ValidateForByteGain(const DataSizeArray& data_size_taken,
                         const CommandSizeArray& cmd_size, uint& max_win,
                         uint& cmd_with_max) {
  for (unsigned int cmd_i = 1; cmd_i < 5; cmd_i++) {
    unsigned int cmd_size_taken = data_size_taken[cmd_i];
    // TODO(@scawful): Replace conditional with table of command sizes
    // "Table that is even with copy but all other cmd are 2"
    auto table_check =
        !(cmd_i == kCommandRepeatingBytes && cmd_size_taken == 3);
    if (cmd_size_taken > max_win && cmd_size_taken > cmd_size[cmd_i] &&
        table_check) {
      printf("==> C:%d / S:%d\n", cmd_i, cmd_size_taken);
      cmd_with_max = cmd_i;
      max_win = cmd_size_taken;
    }
  }
}
 
void CompressionCommandAlternative(const uint8_t* rom_data,
                                   CompressionPiecePointer& compressed_chain,
                                   const CommandSizeArray& cmd_size,
                                   const CommandArgumentArray& cmd_args,
                                   uint& src_data_pos, uint& comp_accumulator,
                                   uint& cmd_with_max, uint& max_win) {
  printf("- Ok we get a gain from %d\n", cmd_with_max);
  std::string buffer;
  buffer.push_back(cmd_args[cmd_with_max][0]);
  if (cmd_size[cmd_with_max] == 2) {
    buffer.push_back(cmd_args[cmd_with_max][1]);
  }
 
  auto new_comp_piece = std::make_shared<CompressionPiece>(
      cmd_with_max, max_win, buffer, cmd_size[cmd_with_max]);
  PrintCompressionPiece(new_comp_piece);
  // If we let non compressed stuff, we need to add a copy chunk before
  if (comp_accumulator != 0) {
    std::string copy_buff;
    copy_buff.resize(comp_accumulator);
    for (int i = 0; i < comp_accumulator; ++i) {
      copy_buff[i] = rom_data[i + src_data_pos - comp_accumulator];
    }
    auto copy_chunk = std::make_shared<CompressionPiece>(
        kCommandDirectCopy, comp_accumulator, copy_buff, comp_accumulator);
    compressed_chain->next = copy_chunk;
    compressed_chain = copy_chunk;
  } else {
    compressed_chain->next = new_comp_piece;
    compressed_chain = new_comp_piece;
  }
  src_data_pos += max_win;
  comp_accumulator = 0;
}
 
void CheckByteRepeatV2(const uint8_t* data, uint& src_pos,
                       const unsigned int last_pos, CompressionCommand& cmd) {
  unsigned int i = 0;
  while (src_pos + i < last_pos && data[src_pos] == data[src_pos + i]) {
    ++i;
  }
  cmd.data_size[kCommandByteFill] = i;
  cmd.arguments[kCommandByteFill][0] = data[src_pos];
}
 
void CheckWordRepeatV2(const uint8_t* data, uint& src_pos,
                       const unsigned int last_pos, CompressionCommand& cmd) {
  if (src_pos + 2 <= last_pos && data[src_pos] != data[src_pos + 1]) {
    unsigned int pos = src_pos;
    char byte1 = data[pos];
    char byte2 = data[pos + 1];
    pos += 2;
    cmd.data_size[kCommandWordFill] = 2;
    while (pos + 1 <= last_pos) {
      if (data[pos] == byte1 && data[pos + 1] == byte2)
        cmd.data_size[kCommandWordFill] += 2;
      else
        break;
      pos += 2;
    }
    cmd.arguments[kCommandWordFill][0] = byte1;
    cmd.arguments[kCommandWordFill][1] = byte2;
  }
}
 
void CheckIncByteV2(const uint8_t* rom_data, uint& src_data_pos,
                    const unsigned int last_pos, CompressionCommand& cmd) {
  unsigned int pos = src_data_pos;
  char byte = rom_data[pos];
  pos++;
  cmd.data_size[kCommandIncreasingFill] = 1;
  byte++;
  while (pos <= last_pos && byte == rom_data[pos]) {
    cmd.data_size[kCommandIncreasingFill]++;
    byte++;
    pos++;
  }
  cmd.arguments[kCommandIncreasingFill][0] = rom_data[src_data_pos];
}
 
void CheckIntraCopyV2(const uint8_t* rom_data, uint& src_data_pos,
                      const unsigned int last_pos, unsigned int start,
                      CompressionCommand& cmd) {
  if (src_data_pos != start) {
    unsigned int searching_pos = start;
    unsigned int current_pos_u = src_data_pos;
    unsigned int copied_size = 0;
    unsigned int search_start = start;
 
    while (searching_pos < src_data_pos && current_pos_u <= last_pos) {
      while (rom_data[current_pos_u] != rom_data[searching_pos] &&
             searching_pos < src_data_pos)
        searching_pos++;
      search_start = searching_pos;
      while (current_pos_u <= last_pos &&
             rom_data[current_pos_u] == rom_data[searching_pos] &&
             searching_pos < src_data_pos) {
        copied_size++;
        current_pos_u++;
        searching_pos++;
      }
      if (copied_size > cmd.data_size[kCommandRepeatingBytes]) {
        search_start -= start;
        printf("- Found repeat of %d at %d\n", copied_size, search_start);
        cmd.data_size[kCommandRepeatingBytes] = copied_size;
        cmd.arguments[kCommandRepeatingBytes][0] = search_start & kSnesByteMax;
        cmd.arguments[kCommandRepeatingBytes][1] = search_start >> 8;
      }
      current_pos_u = src_data_pos;
      copied_size = 0;
    }
  }
}
 
// Table indicating command sizes, in bytes
const std::array<int, 5> kCommandSizes = {1, 2, 2, 2, 3};
 
// TODO(@scawful): TEST ME
void ValidateForByteGainV2(const CompressionCommand& cmd, uint& max_win,
                           uint& cmd_with_max) {
  for (unsigned int cmd_i = 1; cmd_i < 5; cmd_i++) {
    unsigned int cmd_size_taken = cmd.data_size[cmd_i];
    // Check if the command size exceeds the maximum win and the size in the
    // command sizes table, except for the repeating bytes command when the size
    // taken is 3
    if (cmd_size_taken > max_win && cmd_size_taken > kCommandSizes[cmd_i] &&
        !(cmd_i == kCommandRepeatingBytes && cmd_size_taken == 3)) {
      printf("==> C:%d / S:%d\n", cmd_i, cmd_size_taken);
      cmd_with_max = cmd_i;
      max_win = cmd_size_taken;
    }
  }
}
 
void CompressionCommandAlternativeV2(const uint8_t* rom_data,
                                     const CompressionCommand& cmd,
                                     CompressionPiecePointer& compressed_chain,
                                     uint& src_data_pos, uint& comp_accumulator,
                                     uint& cmd_with_max, uint& max_win) {
  printf("- Ok we get a gain from %d\n", cmd_with_max);
  std::string buffer;
  buffer.push_back(cmd.arguments[cmd_with_max][0]);
  if (cmd.cmd_size[cmd_with_max] == 2) {
    buffer.push_back(cmd.arguments[cmd_with_max][1]);
  }
 
  auto new_comp_piece = std::make_shared<CompressionPiece>(
      cmd_with_max, max_win, buffer, cmd.cmd_size[cmd_with_max]);
  PrintCompressionPiece(new_comp_piece);
  // If we let non compressed stuff, we need to add a copy chunk before
  if (comp_accumulator != 0) {
    std::string copy_buff;
    copy_buff.resize(comp_accumulator);
    for (int i = 0; i < comp_accumulator; ++i) {
      copy_buff[i] = rom_data[i + src_data_pos - comp_accumulator];
    }
    auto copy_chunk = std::make_shared<CompressionPiece>(
        kCommandDirectCopy, comp_accumulator, copy_buff, comp_accumulator);
    compressed_chain->next = copy_chunk;
    compressed_chain = copy_chunk;
  } else {
    compressed_chain->next = new_comp_piece;
    compressed_chain = new_comp_piece;
  }
  src_data_pos += max_win;
  comp_accumulator = 0;
}
 
void AddAlternativeCompressionCommand(
    const uint8_t* rom_data, CompressionPiecePointer& compressed_chain,
    const CompressionCommand& command, uint& source_data_position,
    uint& uncompressed_data_size, uint& best_command, uint& best_command_gain) {
  std::cout << "- Identified a gain from command: " << best_command
            << std::endl;
 
  // Create a buffer to store the arguments for the best command.
  std::string argument_buffer;
  argument_buffer.push_back(command.arguments[best_command][0]);
  if (command.cmd_size[best_command] == 2) {
    argument_buffer.push_back(command.arguments[best_command][1]);
  }
 
  // Create a new compression piece for the best command.
  auto new_compression_piece = std::make_shared<CompressionPiece>(
      best_command, best_command_gain, argument_buffer,
      command.cmd_size[best_command]);
  PrintCompressionPiece(new_compression_piece);
 
  // If there is uncompressed data, create a direct copy compression piece for
  // it.
  if (uncompressed_data_size != 0) {
    std::string copy_buffer(uncompressed_data_size, 0);
    for (int i = 0; i < uncompressed_data_size; ++i) {
      copy_buffer[i] =
          rom_data[i + source_data_position - uncompressed_data_size];
    }
    auto direct_copy_piece = std::make_shared<CompressionPiece>(
        kCommandDirectCopy, uncompressed_data_size, copy_buffer,
        uncompressed_data_size);
 
    // Append the direct copy piece to the chain.
    compressed_chain->next = direct_copy_piece;
    compressed_chain = direct_copy_piece;
  }
 
  // Append the new compression piece to the chain.
  compressed_chain->next = new_compression_piece;
  compressed_chain = new_compression_piece;
 
  // Update the position in the source data and reset the uncompressed data
  // size.
  source_data_position += best_command_gain;
  uncompressed_data_size = 0;
}
 
absl::StatusOr<CompressionPiecePointer> SplitCompressionPiece(
    CompressionPiecePointer& piece, int mode) {
  CompressionPiecePointer new_piece;
  unsigned int length_left = piece->length - kMaxLengthCompression;
  piece->length = kMaxLengthCompression;
 
  switch (piece->command) {
    case kCommandByteFill:
    case kCommandWordFill:
      new_piece = std::make_shared<CompressionPiece>(
          piece->command, length_left, piece->argument, piece->argument_length);
      break;
    case kCommandIncreasingFill:
      new_piece = std::make_shared<CompressionPiece>(
          piece->command, length_left, piece->argument, piece->argument_length);
      new_piece->argument[0] =
          (char)(piece->argument[0] + kMaxLengthCompression);
      break;
    case kCommandDirectCopy: {
      std::string empty;
      piece->argument_length = kMaxLengthCompression;
      new_piece = std::make_shared<CompressionPiece>(
          piece->command, length_left, empty, length_left);
      // MEMCPY
      for (int i = 0; i < length_left; ++i) {
        new_piece->argument[i] = piece->argument[i + kMaxLengthCompression];
      }
      break;
    }
    case kCommandRepeatingBytes: {
      piece->argument_length = kMaxLengthCompression;
      unsigned int offset = piece->argument[0] + (piece->argument[1] << 8);
      new_piece = std::make_shared<CompressionPiece>(
          piece->command, length_left, piece->argument, piece->argument_length);
      if (mode == kNintendoMode2) {
        new_piece->argument[0] =
            (offset + kMaxLengthCompression) & kSnesByteMax;
        new_piece->argument[1] = (offset + kMaxLengthCompression) >> 8;
      }
      if (mode == kNintendoMode1) {
        new_piece->argument[1] =
            (offset + kMaxLengthCompression) & kSnesByteMax;
        new_piece->argument[0] = (offset + kMaxLengthCompression) >> 8;
      }
    } break;
    default: {
      return absl::InvalidArgumentError(
          "SplitCompressionCommand: Invalid Command");
    }
  }
  return new_piece;
}
 
std::vector<uint8_t> CreateCompressionString(CompressionPiecePointer& start,
                                             int mode) {
  unsigned int pos = 0;
  auto piece = start;
  std::vector<uint8_t> output;
 
  while (piece != nullptr) {
    if (piece->length <= kMaxLengthNormalHeader) {  // Normal header
      output.push_back(BUILD_HEADER(piece->command, piece->length));
      pos++;
    } else {
      if (piece->length <= kMaxLengthCompression) {
        output.push_back(kCompressionStringMod |
                         ((uint8_t)piece->command << 2) |
                         (((piece->length - 1) & 0xFF00) >> 8));
        pos++;
        printf("Building extended header : cmd: %d, length: %d -  %02X\n",
               piece->command, piece->length, output[pos - 1]);
        output.push_back(((piece->length - 1) & 0x00FF));  // (char)
        pos++;
      } else {
        // We need to split the command
        auto new_piece = SplitCompressionPiece(piece, mode);
        if (!new_piece.ok()) {
          std::cout << new_piece.status().ToString() << std::endl;
        }
        printf("New added piece\n");
        auto piece_data = new_piece.value();
        PrintCompressionPiece(piece_data);
        piece_data->next = piece->next;
        piece->next = piece_data;
        continue;
      }
    }
 
    if (piece->command == kCommandRepeatingBytes) {
      char tmp[2];
      tmp[0] = piece->argument[0];
      tmp[1] = piece->argument[1];
      if (mode == kNintendoMode1) {
        tmp[0] = piece->argument[1];
        tmp[1] = piece->argument[0];
      }
      for (const auto& each : tmp) {
        output.push_back(each);
        pos++;
      }
    } else {
      for (int i = 0; i < piece->argument_length; ++i) {
        output.push_back(piece->argument[i]);
        pos++;
      }
    }
    pos += piece->argument_length;
    piece = piece->next;
  }
  output.push_back(kSnesByteMax);
  return output;
}
 
absl::Status ValidateCompressionResult(CompressionPiecePointer& chain_head,
                                       int mode, int start, int src_data_pos) {
  if (chain_head->next != nullptr) {
    Rom temp_rom;
    RETURN_IF_ERROR(
        temp_rom.LoadFromData(CreateCompressionString(chain_head->next, mode)))
    ASSIGN_OR_RETURN(
        auto decomp_data,
        DecompressV2(temp_rom.data(), 0, temp_rom.size(), 1, temp_rom.size()));
    if (!std::equal(decomp_data.begin() + start, decomp_data.end(),
                    temp_rom.begin())) {
      return absl::InternalError(absl::StrFormat(
          "Compressed data does not match uncompressed data at %d\n",
          (uint)(src_data_pos - start)));
    }
  }
  return absl::OkStatus();
}
 
// Merge consecutive copy if possible
CompressionPiecePointer MergeCopy(CompressionPiecePointer& start) {
  CompressionPiecePointer piece = start;
 
  while (piece != nullptr) {
    if (piece->command == kCommandDirectCopy && piece->next != nullptr &&
        piece->next->command == kCommandDirectCopy &&
        piece->length + piece->next->length <= kMaxLengthCompression) {
      unsigned int previous_length = piece->length;
      piece->length = piece->length + piece->next->length;
 
      for (int i = 0; i < piece->next->argument_length; ++i) {
        piece->argument[i + previous_length] = piece->next->argument[i];
      }
      piece->argument_length = piece->length;
      PrintCompressionPiece(piece);
 
      auto p_next_next = piece->next->next;
      piece->next = p_next_next;
      continue;  // Next could be another copy
    }
    piece = piece->next;
  }
  return start;
}
 
absl::StatusOr<std::vector<uint8_t>> CompressV2(const uint8_t* data,
                                                const int start,
                                                const int length, int mode,
                                                bool check) {
  // Surely there's no need to compress zero...
  if (length == 0) {
    return std::vector<uint8_t>();
  }
 
  // Worst case should be a copy of the string with extended header
  std::string worst_case = "aaa";
  auto compressed_chain =
      std::make_shared<CompressionPiece>(1, 1, worst_case, 2);
  auto compressed_chain_start = compressed_chain;
 
  CompressionCommand current_cmd = {/*argument*/ {{}},
                                    /*cmd_size*/ {0, 1, 2, 1, 2},
                                    /*data_size*/ {0, 0, 0, 0, 0}};
 
  unsigned int src_pos = start;
  unsigned int last_pos = start + length - 1;
  unsigned int comp_accumulator = 0;  // Used when skipping using copy
 
  while (true) {
    current_cmd.data_size.fill({});
    current_cmd.arguments.fill({{}});
 
    CheckByteRepeatV2(data, src_pos, last_pos, current_cmd);
    CheckWordRepeatV2(data, src_pos, last_pos, current_cmd);
    CheckIncByteV2(data, src_pos, last_pos, current_cmd);
    CheckIntraCopyV2(data, src_pos, last_pos, start, current_cmd);
 
    unsigned int max_win = 2;
    unsigned int cmd_with_max = kCommandDirectCopy;
    ValidateForByteGain(current_cmd.data_size, current_cmd.cmd_size, max_win,
                        cmd_with_max);
    // ValidateForByteGainV2(current_cmd, max_win, cmd_with_max);
 
    if (cmd_with_max == kCommandDirectCopy) {
      // This is the worst case scenario
      // Progress through the next byte, in case there's a different
      // compression command we can implement before we hit 32 bytes.
      src_pos++;
      comp_accumulator++;
 
      // Arbitrary choice to do a 32 bytes grouping for copy.
      if (comp_accumulator == 32 || src_pos > last_pos) {
        std::string buffer = SetBuffer(data, src_pos, comp_accumulator);
        auto new_comp_piece = std::make_shared<CompressionPiece>(
            kCommandDirectCopy, comp_accumulator, buffer, comp_accumulator);
        compressed_chain->next = new_comp_piece;
        comp_accumulator = 0;
      }
    } else {
      AddAlternativeCompressionCommand(data, compressed_chain, current_cmd,
                                       src_pos, comp_accumulator, cmd_with_max,
                                       max_win);
    }
 
    if (src_pos > last_pos) {
      printf("Breaking compression loop\n");
      break;
    }
 
    if (check) {
      RETURN_IF_ERROR(ValidateCompressionResult(compressed_chain_start, mode,
                                                start, src_pos))
    }
  }
 
  // Skipping compression chain header
  MergeCopy(compressed_chain_start->next);
  PrintCompressionChain(compressed_chain_start);
  return CreateCompressionString(compressed_chain_start->next, mode);
}
 
absl::StatusOr<std::vector<uint8_t>> CompressGraphics(const uint8_t* data,
                                                      const int pos,
                                                      const int length) {
  return CompressV2(data, pos, length, kNintendoMode2);
}
 
absl::StatusOr<std::vector<uint8_t>> CompressOverworld(const uint8_t* data,
                                                       const int pos,
                                                       const int length) {
  return CompressV2(data, pos, length, kNintendoMode1);
}
 
absl::StatusOr<std::vector<uint8_t>> CompressOverworld(
    const std::vector<uint8_t> data, const int pos, const int length) {
  return CompressV3(data, pos, length, kNintendoMode1);
}
 
void CheckByteRepeatV3(CompressionContext& context) {
  unsigned int pos = context.src_pos;
 
  // Ensure the sequence does not start with an uncompressable byte
  if (pos == 0 || context.data[pos - 1] != context.data[pos]) {
    char byte_to_repeat = context.data[pos];
    while (pos <= context.last_pos && context.data[pos] == byte_to_repeat) {
      context.current_cmd.data_size[kCommandByteFill]++;
      pos++;
    }
 
    context.current_cmd.arguments[kCommandByteFill][0] = byte_to_repeat;
 
    // Added debug log
    DEBUG_LOG("CheckByteRepeatV3: byte_to_repeat = "
              << (int)byte_to_repeat << ", size = "
              << context.current_cmd.data_size[kCommandByteFill]);
  }
}
 
void CheckWordRepeatV3(CompressionContext& context) {
  if (context.src_pos + 1 <= context.last_pos) {  // Changed the condition here
    unsigned int pos = context.src_pos;
    char byte1 = context.data[pos];
    char byte2 = context.data[pos + 1];
    pos += 2;
    context.current_cmd.data_size[kCommandWordFill] = 2;
    while (pos + 1 <= context.last_pos) {
      if (context.data[pos] == byte1 && context.data[pos + 1] == byte2)
        context.current_cmd.data_size[kCommandWordFill] += 2;
      else
        break;
      pos += 2;
    }
 
    context.current_cmd.arguments[kCommandWordFill][0] = byte1;
    context.current_cmd.arguments[kCommandWordFill][1] = byte2;
  }
 
  DEBUG_LOG("CheckWordRepeatV3: byte1 = "
            << (int)context.current_cmd.arguments[kCommandWordFill][0]
            << ", byte2 = "
            << (int)context.current_cmd.arguments[kCommandWordFill][1]
            << ", size = " << context.current_cmd.data_size[kCommandWordFill]);
}
 
void CheckIncByteV3(CompressionContext& context) {
  unsigned int pos = context.src_pos;
  uint8_t byte = context.data[pos];
  pos++;
  context.current_cmd.data_size[kCommandIncreasingFill] = 1;
  byte++;
 
  while (pos <= context.last_pos && byte == context.data[pos]) {
    context.current_cmd.data_size[kCommandIncreasingFill]++;
    byte++;
    pos++;
  }
 
  // Let's see if the sequence is surrounded by identical bytes and if so,
  // consider if a direct copy is better.
  if (context.current_cmd.data_size[kCommandIncreasingFill] == 3 &&
      context.src_pos > 0 && pos < context.data.size() &&
      context.data[context.src_pos - 1] == context.data[pos]) {
    context.current_cmd.data_size[kCommandIncreasingFill] =
        0;  // Reset the size to 0 to prioritize direct copy
    return;
  }
 
  context.current_cmd.arguments[kCommandIncreasingFill][0] =
      context.data[context.src_pos];
 
  DEBUG_LOG("CheckIncByteV3: byte = "
            << (int)context.current_cmd.arguments[kCommandIncreasingFill][0]
            << ", size = "
            << context.current_cmd.data_size[kCommandIncreasingFill]);
}
 
void CheckIntraCopyV3(CompressionContext& context) {
  const int window_size =
      32;  // This can be adjusted for optimal performance and results
 
  // We'll only search for repeating sequences if we're not at the very
  // beginning
  if (context.src_pos > 0 &&
      context.src_pos + window_size <= context.data.size()) {
    unsigned int max_copied_size = 0;
    unsigned int best_search_start = 0;
 
    // Slide the window over the source data
    for (int win_pos = 1; win_pos < window_size && win_pos < context.src_pos;
         ++win_pos) {
      auto start_search_from = context.data.begin() + context.src_pos - win_pos;
      auto search_end = context.data.begin() + context.src_pos;
 
      // Use std::search to find the sequence in the window in the previous
      // source data
      auto found_pos = std::search(
          start_search_from, search_end, context.data.begin() + context.src_pos,
          context.data.begin() + context.src_pos + win_pos);
 
      if (found_pos != search_end) {
        // Check the entire length of the match
        unsigned int len = 0;
        while (context.src_pos + len < context.data.size() &&
               context.data[context.src_pos + len] == *(found_pos + len)) {
          len++;
        }
 
        if (len > max_copied_size) {
          max_copied_size = len;
          best_search_start = found_pos - context.data.begin();
        }
      }
    }
 
    if (max_copied_size >
        context.current_cmd.data_size[kCommandRepeatingBytes]) {
      DEBUG_LOG("CheckIntraCopyV3: Detected repeating sequence of length "
                << max_copied_size << " starting from " << best_search_start);
      context.current_cmd.data_size[kCommandRepeatingBytes] = max_copied_size;
      context.current_cmd.arguments[kCommandRepeatingBytes][0] =
          best_search_start & kSnesByteMax;
      context.current_cmd.arguments[kCommandRepeatingBytes][1] =
          best_search_start >> 8;
    }
 
    DEBUG_LOG("CheckIntraCopyV3: max_copied_size = " << max_copied_size
                                                     << ", best_search_start = "
                                                     << best_search_start);
  }
}
 
void InitializeCompression(CompressionContext& context) {
  // Initialize the current_cmd with default values.
  context.current_cmd = {/*argument*/ {{}},
                         /*cmd_size*/ {0, 1, 2, 1, 2},
                         /*data_size*/ {0, 0, 0, 0, 0}};
}
 
void CheckAvailableCompressionCommands(CompressionContext& context) {
  // Reset the data_size and arguments for a fresh check.
  context.current_cmd.data_size.fill({});
  context.current_cmd.arguments.fill({{}});
 
  CheckByteRepeatV3(context);
  CheckWordRepeatV3(context);
  CheckIncByteV3(context);
  CheckIntraCopyV3(context);
 
  DEBUG_LOG("CheckAvailableCompressionCommands: src_pos = " << context.src_pos);
}
 
void DetermineBestCompression(CompressionContext& context) {
  int max_net_savings = -1;  // Adjusted the bias to consider any savings
 
  // Start with the default scenario.
  context.cmd_with_max = kCommandDirectCopy;
 
  for (unsigned int cmd_i = 1; cmd_i < 5; cmd_i++) {
    unsigned int cmd_size_taken = context.current_cmd.data_size[cmd_i];
    int net_savings = cmd_size_taken - context.current_cmd.cmd_size[cmd_i];
 
    // Skip commands that aren't efficient.
    if (cmd_size_taken <= 2 && cmd_i != kCommandDirectCopy) {
      continue;
    }
 
    // Check surrounding data for optimization.
    if (context.src_pos > 0 &&
        context.src_pos + cmd_size_taken < context.data.size()) {
      char prev_byte = context.data[context.src_pos - 1];
      char next_byte = context.data[context.src_pos + cmd_size_taken];
      if (prev_byte != next_byte && cmd_size_taken == 3) {
        continue;
      }
    }
 
    // Check if the current command offers more net savings.
    if (net_savings > max_net_savings) {
      context.cmd_with_max = cmd_i;
      max_net_savings = net_savings;
    }
  }
 
  DEBUG_LOG("DetermineBestCompression: cmd_with_max = "
            << context.cmd_with_max << ", data_size = "
            << context.current_cmd.data_size[context.cmd_with_max]);
}
 
void HandleDirectCopy(CompressionContext& context) {
  // If the next best compression method isn't direct copy and we have bytes
  // accumulated for direct copy, flush them out.
  if (context.cmd_with_max != kCommandDirectCopy &&
      context.comp_accumulator > 0) {
    uint8_t header = BUILD_HEADER(kCommandDirectCopy, context.comp_accumulator);
    context.compressed_data.push_back(header);
    std::vector<uint8_t> uncompressed_data(
        context.data.begin() + context.src_pos - context.comp_accumulator,
        context.data.begin() + context.src_pos);
    context.compressed_data.insert(context.compressed_data.end(),
                                   uncompressed_data.begin(),
                                   uncompressed_data.end());
    context.comp_accumulator = 0;
    return;
  }
 
  // If the next best compression method is not direct copy and we haven't
  // accumulated any bytes, treat it as a single byte direct copy.
  if (context.cmd_with_max != kCommandDirectCopy &&
      context.comp_accumulator == 0) {
    context.compressed_data.push_back(
        0x00);  // Command for a single byte direct copy
    context.compressed_data.push_back(
        context.data[context.src_pos]);  // The single byte
    context.src_pos++;
    return;
  }
 
  // If we reach here, accumulate bytes for a direct copy.
  context.src_pos++;
  context.comp_accumulator++;
 
  // If we've accumulated the maximum bytes for a direct copy command or
  // reached the end, flush them.
  if (context.comp_accumulator >= 32 || context.src_pos > context.last_pos) {
    uint8_t header = BUILD_HEADER(kCommandDirectCopy, context.comp_accumulator);
    context.compressed_data.push_back(header);
    std::vector<uint8_t> uncompressed_data(
        context.data.begin() + context.src_pos - context.comp_accumulator,
        context.data.begin() + context.src_pos);
    context.compressed_data.insert(context.compressed_data.end(),
                                   uncompressed_data.begin(),
                                   uncompressed_data.end());
    context.comp_accumulator = 0;
  }
 
  DEBUG_LOG("HandleDirectCopy: src_pos = " << context.src_pos
                                           << ", compressed_data size = "
                                           << context.compressed_data.size());
}
 
void AddCompressionToChain(CompressionContext& context) {
  DEBUG_LOG("AddCompressionToChain: Adding command arguments: ");
 
  // If there's uncompressed data, add a copy chunk before the compression
  // command
  if (context.comp_accumulator != 0) {
    uint8_t header = BUILD_HEADER(kCommandDirectCopy, context.comp_accumulator);
    context.compressed_data.push_back(header);
    std::vector<uint8_t> uncompressed_data(
        context.data.begin() + context.src_pos - context.comp_accumulator,
        context.data.begin() + context.src_pos);
    context.compressed_data.insert(context.compressed_data.end(),
                                   uncompressed_data.begin(),
                                   uncompressed_data.end());
    context.comp_accumulator = 0;
  }
 
  // Now, add the compression command
  uint8_t header =
      BUILD_HEADER(context.cmd_with_max,
                   context.current_cmd.data_size[context.cmd_with_max]);
  context.compressed_data.push_back(header);
 
  DEBUG_LOG("AddCompressionToChain: (Before) src_pos = "
            << context.src_pos
            << ", compressed_data size = " << context.compressed_data.size());
 
  // Add the command arguments to the compressed_data vector
  context.compressed_data.push_back(
      context.current_cmd.arguments[context.cmd_with_max][0]);
  if (context.current_cmd.cmd_size[context.cmd_with_max] == 2) {
    context.compressed_data.push_back(
        context.current_cmd.arguments[context.cmd_with_max][1]);
  }
 
  context.src_pos += context.current_cmd.data_size[context.cmd_with_max];
  context.comp_accumulator = 0;
 
  DEBUG_LOG("AddCompressionToChain: (After) src_pos = "
            << context.src_pos
            << ", compressed_data size = " << context.compressed_data.size());
}
 
absl::Status ValidateCompressionResultV3(const CompressionContext& context) {
  if (!context.compressed_data.empty()) {
    Rom temp_rom;
    RETURN_IF_ERROR(temp_rom.LoadFromData(context.compressed_data));
    ASSIGN_OR_RETURN(
        auto decomp_data,
        DecompressV2(temp_rom.data(), 0, temp_rom.size(), 1, temp_rom.size()));
 
    if (!std::equal(decomp_data.begin() + context.start, decomp_data.end(),
                    temp_rom.begin())) {
      return absl::InternalError(absl::StrFormat(
          "Compressed data does not match uncompressed data at %d\n",
          (context.src_pos - context.start)));
    }
  }
  return absl::OkStatus();
}
 
absl::StatusOr<CompressionPiece> SplitCompressionPieceV3(
    CompressionPiece& piece, int mode) {
  CompressionPiece new_piece;
  unsigned int length_left = piece.length - kMaxLengthCompression;
  piece.length = kMaxLengthCompression;
 
  switch (piece.command) {
    case kCommandByteFill:
    case kCommandWordFill:
      new_piece = CompressionPiece(piece.command, length_left, piece.argument,
                                   piece.argument_length);
      break;
    case kCommandIncreasingFill:
      new_piece = CompressionPiece(piece.command, length_left, piece.argument,
                                   piece.argument_length);
      new_piece.argument[0] = (char)(piece.argument[0] + kMaxLengthCompression);
      break;
    case kCommandDirectCopy: {
      piece.argument_length = kMaxLengthCompression;
      std::string empty_string = "";
      new_piece = CompressionPiece(piece.command, length_left, empty_string,
                                   length_left);
      // MEMCPY
      for (int i = 0; i < length_left; ++i) {
        new_piece.argument[i] = piece.argument[i + kMaxLengthCompression];
      }
      break;
    }
    case kCommandRepeatingBytes: {
      piece.argument_length = kMaxLengthCompression;
      unsigned int offset = piece.argument[0] + (piece.argument[1] << 8);
      new_piece = CompressionPiece(piece.command, length_left, piece.argument,
                                   piece.argument_length);
      if (mode == kNintendoMode2) {
        new_piece.argument[0] = (offset + kMaxLengthCompression) & kSnesByteMax;
        new_piece.argument[1] = (offset + kMaxLengthCompression) >> 8;
      }
      if (mode == kNintendoMode1) {
        new_piece.argument[1] = (offset + kMaxLengthCompression) & kSnesByteMax;
        new_piece.argument[0] = (offset + kMaxLengthCompression) >> 8;
      }
    } break;
    default: {
      return absl::InvalidArgumentError(
          "SplitCompressionCommand: Invalid Command");
    }
  }
 
  return new_piece;
}
 
void FinalizeCompression(CompressionContext& context) {
  unsigned int pos = 0;
 
  for (CompressionPiece& piece : context.compression_pieces) {
    if (piece.length <= kMaxLengthNormalHeader) {  // Normal Header
      context.compression_string.push_back(
          BUILD_HEADER(piece.command, piece.length));
      pos++;
    } else {
      if (piece.length <= kMaxLengthCompression) {
        context.compression_string.push_back(
            kCompressionStringMod | ((uint8_t)piece.command << 2) |
            (((piece.length - 1) & 0xFF00) >> 8));
        pos++;
        std::cout << "Building extended header : cmd: " << piece.command
                  << ", length: " << piece.length << " - "
                  << (int)context.compression_string[pos - 1] << std::endl;
        context.compression_string.push_back(
            ((piece.length - 1) & 0x00FF));  // (char)
      } else {
        // We need to split the command
        auto new_piece = SplitCompressionPieceV3(piece, context.mode);
        if (!new_piece.ok()) {
          std::cout << new_piece.status().ToString() << std::endl;
        }
        context.compression_pieces.insert(
            context.compression_pieces.begin() + pos + 1, new_piece.value());
        continue;
      }
    }
 
    if (piece.command == kCommandRepeatingBytes) {
      char tmp[2];
      tmp[0] = piece.argument[0];
      tmp[1] = piece.argument[1];
      if (context.mode == kNintendoMode1) {
        tmp[0] = piece.argument[1];
        tmp[1] = piece.argument[0];
      }
      for (const auto& each : tmp) {
        context.compression_string.push_back(each);
        pos++;
      }
    } else {
      for (int i = 0; i < piece.argument_length; ++i) {
        context.compression_string.push_back(piece.argument[i]);
        pos++;
      }
    }
    pos += piece.argument_length;
  }
 
  // Add any remaining uncompressed data
  if (context.comp_accumulator > 0) {
    context.compressed_data.insert(
        context.compressed_data.end(),
        context.data.begin() + context.src_pos - context.comp_accumulator,
        context.data.begin() + context.src_pos);
    context.comp_accumulator = 0;
  }
 
  // Add the end marker to the compressed data
  context.compressed_data.push_back(kSnesByteMax);
  DEBUG_LOG("FinalizeCompression: compressed_data size = "
            << context.compressed_data.size());
}
 
absl::StatusOr<std::vector<uint8_t>> CompressV3(
    const std::vector<uint8_t>& data, const int start, const int length,
    int mode, bool check) {
  if (length == 0) {
    return std::vector<uint8_t>();
  }
 
  CompressionContext context(data, start, length, mode);
  InitializeCompression(context);
 
  while (context.src_pos <= context.last_pos) {
    CheckAvailableCompressionCommands(context);
    DetermineBestCompression(context);
 
    DEBUG_LOG("CompressV3 Loop: cmd_with_max = " << context.cmd_with_max);
 
    if (context.cmd_with_max == kCommandDirectCopy) {
      HandleDirectCopy(context);
    } else {
      AddCompressionToChain(context);
    }
 
    if (check) {
      RETURN_IF_ERROR(ValidateCompressionResultV3(context))
    }
  }
 
  FinalizeCompression(context);
  return std::vector<uint8_t>(context.compressed_data.begin(),
                              context.compressed_data.end());
}
 
std::string SetBuffer(const uint8_t* data, int src_pos, int comp_accumulator) {
  std::string buffer;
  for (int i = 0; i < comp_accumulator; ++i) {
    buffer.push_back(data[i + src_pos - comp_accumulator]);
  }
  return buffer;
}
 
std::string SetBuffer(const std::vector<uint8_t>& data, int src_pos,
                      int comp_accumulator) {
  std::string buffer;
  for (int i = 0; i < comp_accumulator; ++i) {
    buffer.push_back(data[i + src_pos - comp_accumulator]);
  }
  return buffer;
}
 
void memfill(const uint8_t* data, std::vector<uint8_t>& buffer, int buffer_pos,
             int offset, int length) {
  auto a = data[offset];
  auto b = data[offset + 1];
  for (int i = 0; i < length; i = i + 2) {
    buffer[buffer_pos + i] = a;
    if ((i + 1) < length)
      buffer[buffer_pos + i + 1] = b;
  }
}
 
absl::StatusOr<std::vector<uint8_t>> DecompressV2(const uint8_t* data,
                                                  int offset, int size,
                                                  int mode, size_t rom_size) {
  if (size == 0) {
    return std::vector<uint8_t>();
  }
 
  // Validate initial offset is within bounds (if rom_size provided)
  // rom_size == static_cast<size_t>(-1) means "no bounds checking"
  if (rom_size != static_cast<size_t>(-1) &&
      (offset < 0 || static_cast<size_t>(offset) >= rom_size)) {
    return absl::OutOfRangeError(
        absl::StrFormat("DecompressV2: Initial offset %d exceeds ROM size %zu",
                        offset, rom_size));
  }
 
  std::vector<uint8_t> buffer(size, 0);
  unsigned int length = 0;
  unsigned int buffer_pos = 0;
  uint8_t command = 0;
 
  // Bounds check before initial header read
  if (rom_size != static_cast<size_t>(-1) &&
      static_cast<size_t>(offset) >= rom_size) {
    return absl::OutOfRangeError(
        absl::StrFormat("DecompressV2: Initial offset %d exceeds ROM size %zu",
                        offset, rom_size));
  }
  uint8_t header = data[offset];
 
  while (header != kSnesByteMax) {
    // Bounds check before reading command (if rom_size provided)
    if (rom_size != static_cast<size_t>(-1) &&
        static_cast<size_t>(offset) >= rom_size) {
      return absl::OutOfRangeError(absl::StrFormat(
          "DecompressV2: Offset %d exceeds ROM size %zu while reading command",
          offset, rom_size));
    }
 
    if ((header & kExpandedMod) == kExpandedMod) {
      // Expanded Command - needs 2 bytes
      if (rom_size != static_cast<size_t>(-1) &&
          static_cast<size_t>(offset + 1) >= rom_size) {
        return absl::OutOfRangeError(
            absl::StrFormat("DecompressV2: Offset %d+1 exceeds ROM size %zu "
                            "for expanded command",
                            offset, rom_size));
      }
      command = ((header >> 2) & kCommandMod);
      length = (((header << 8) | data[offset + 1]) & kExpandedLengthMod);
      offset += 2;  // Advance 2 bytes in ROM
    } else {
      // Normal Command
      command = ((header >> 5) & kCommandMod);
      length = (header & kNormalLengthMod);
      offset += 1;  // Advance 1 byte in ROM
    }
    length += 1;  // each commands is at least of size 1 even if index 00
 
    // CRITICAL: Check and resize buffer BEFORE any command writes
    // This prevents WASM "index out of bounds" errors
    // The buffer may need to grow if decompressed data exceeds initial size
    if (buffer_pos + length > static_cast<unsigned int>(size)) {
      // Double the buffer size (with overflow protection)
      int new_size = size;
      while (buffer_pos + length > static_cast<unsigned int>(new_size)) {
        if (new_size > INT_MAX / 2) {
          return absl::ResourceExhaustedError(absl::StrFormat(
              "DecompressV2: Buffer size overflow at pos %u, length %u",
              buffer_pos, length));
        }
        new_size *= 2;
      }
      size = new_size;
      buffer.resize(size);
    }
 
    switch (command) {
      case kCommandDirectCopy:  // Does not advance in the ROM
        // Bounds check for direct copy
        if (rom_size != static_cast<size_t>(-1) &&
            static_cast<size_t>(offset + length) > rom_size) {
          return absl::OutOfRangeError(
              absl::StrFormat("DecompressV2: DirectCopy offset %d + length %u "
                              "exceeds ROM size %zu",
                              offset, length, rom_size));
        }
        memcpy(buffer.data() + buffer_pos, data + offset, length);
        buffer_pos += length;
        offset += length;
        break;
      case kCommandByteFill:
        // Bounds check for byte fill
        if (rom_size != static_cast<size_t>(-1) &&
            static_cast<size_t>(offset) >= rom_size) {
          return absl::OutOfRangeError(absl::StrFormat(
              "DecompressV2: ByteFill offset %d exceeds ROM size %zu", offset,
              rom_size));
        }
        memset(buffer.data() + buffer_pos, (int)(data[offset]), length);
        buffer_pos += length;
        offset += 1;  // Advances 1 byte in the ROM
        break;
      case kCommandWordFill:
        // Bounds check for word fill (needs 2 bytes)
        if (rom_size != static_cast<size_t>(-1) &&
            static_cast<size_t>(offset + 1) >= rom_size) {
          return absl::OutOfRangeError(absl::StrFormat(
              "DecompressV2: WordFill offset %d+1 exceeds ROM size %zu", offset,
              rom_size));
        }
        memfill(data, buffer, buffer_pos, offset, length);
        buffer_pos += length;
        offset += 2;  // Advance 2 byte in the ROM
        break;
      case kCommandIncreasingFill: {
        // Bounds check for increasing fill
        if (rom_size != static_cast<size_t>(-1) &&
            static_cast<size_t>(offset) >= rom_size) {
          return absl::OutOfRangeError(absl::StrFormat(
              "DecompressV2: IncreasingFill offset %d exceeds ROM size %zu",
              offset, rom_size));
        }
        auto inc_byte = data[offset];
        for (unsigned int i = 0; i < length; i++) {
          buffer[buffer_pos] = inc_byte++;
          buffer_pos++;
        }
        offset += 1;  // Advance 1 byte in the ROM
      } break;
      case kCommandRepeatingBytes: {
        // Bounds check for repeating bytes (needs 2 bytes)
        if (rom_size != static_cast<size_t>(-1) &&
            static_cast<size_t>(offset + 1) >= rom_size) {
          return absl::OutOfRangeError(absl::StrFormat(
              "DecompressV2: RepeatingBytes offset %d+1 exceeds ROM size %zu",
              offset, rom_size));
        }
        uint16_t s1 = ((data[offset + 1] & kSnesByteMax) << 8);
        uint16_t s2 = (data[offset] & kSnesByteMax);
        int addr = (s1 | s2);
        if (mode == kNintendoMode1) {  // Reversed byte order for
                                       // overworld maps
          addr = (data[offset + 1] & kSnesByteMax) |
                 ((data[offset] & kSnesByteMax) << 8);
        }
        if (addr > offset) {
          return absl::InternalError(
              absl::StrFormat("Decompress: Offset for command copy exceeds "
                              "current position "
                              "(Offset : %#04x | Pos : %#06x)\n",
                              addr, offset));
        }
        // Buffer resize already done above, no need to check again
        memcpy(buffer.data() + buffer_pos, buffer.data() + addr, length);
        buffer_pos += length;
        offset += 2;
      } break;
      default: {
        std::cout << absl::StrFormat(
            "Decompress: Invalid header (Offset : %#06x, Command: %#04x)\n",
            offset, command);
      } break;
    }
    // Bounds check before reading next header byte
    if (rom_size != static_cast<size_t>(-1) &&
        static_cast<size_t>(offset) >= rom_size) {
      return absl::OutOfRangeError(
          absl::StrFormat("DecompressV2: Offset %d exceeds ROM size %zu while "
                          "reading next header",
                          offset, rom_size));
    }
    header = data[offset];
  }
 
  return buffer;
}
 
absl::StatusOr<std::vector<uint8_t>> DecompressGraphics(const uint8_t* data,
                                                        int pos, int size) {
  return DecompressV2(data, pos, size, kNintendoMode2);
}
 
absl::StatusOr<std::vector<uint8_t>> DecompressOverworld(const uint8_t* data,
                                                         int pos, int size) {
  return DecompressV2(data, pos, size, kNintendoMode1);
}
 
absl::StatusOr<std::vector<uint8_t>> DecompressOverworld(
    const std::vector<uint8_t> data, int pos, int size) {
  return DecompressV2(data.data(), pos, size, kNintendoMode1);
}
 
}  // namespace lc_lz2
}  // namespace gfx
}  // namespace yaze