decomp.cpp

//S-DD1 decompression algorithm implementation
//original code written by Andreas Naive (public domain license)
//bsnes port written by byuu

//note: decompression module does not need to be serialized with bsnes
//this is because decompression only runs during DMA, and bsnes will complete
//any pending DMA transfers prior to serialization.

//input manager

void SDD1::Decomp::IM::init(unsigned offset_) {
  offset = offset_;
  bit_count = 4;
}

uint8 SDD1::Decomp::IM::get_codeword(uint8 code_length) {
  uint8 codeword;
  uint8 comp_count;

  codeword = self.rom_read(offset) << bit_count;
  bit_count++;

  if(codeword & 0x80) {
    codeword |= self.rom_read(offset + 1) >> (9 - bit_count);
    bit_count += code_length;
  }

  if(bit_count & 0x08) {
    offset++;
    bit_count &= 0x07;
  }

  return codeword;
}

//golomb-code decoder

const uint8 SDD1::Decomp::GCD::run_count[] = {
  0x00, 0x00, 0x01, 0x00, 0x03, 0x01, 0x02, 0x00,
  0x07, 0x03, 0x05, 0x01, 0x06, 0x02, 0x04, 0x00,
  0x0f, 0x07, 0x0b, 0x03, 0x0d, 0x05, 0x09, 0x01,
  0x0e, 0x06, 0x0a, 0x02, 0x0c, 0x04, 0x08, 0x00,
  0x1f, 0x0f, 0x17, 0x07, 0x1b, 0x0b, 0x13, 0x03,
  0x1d, 0x0d, 0x15, 0x05, 0x19, 0x09, 0x11, 0x01,
  0x1e, 0x0e, 0x16, 0x06, 0x1a, 0x0a, 0x12, 0x02,
  0x1c, 0x0c, 0x14, 0x04, 0x18, 0x08, 0x10, 0x00,
  0x3f, 0x1f, 0x2f, 0x0f, 0x37, 0x17, 0x27, 0x07,
  0x3b, 0x1b, 0x2b, 0x0b, 0x33, 0x13, 0x23, 0x03,
  0x3d, 0x1d, 0x2d, 0x0d, 0x35, 0x15, 0x25, 0x05,
  0x39, 0x19, 0x29, 0x09, 0x31, 0x11, 0x21, 0x01,
  0x3e, 0x1e, 0x2e, 0x0e, 0x36, 0x16, 0x26, 0x06,
  0x3a, 0x1a, 0x2a, 0x0a, 0x32, 0x12, 0x22, 0x02,
  0x3c, 0x1c, 0x2c, 0x0c, 0x34, 0x14, 0x24, 0x04,
  0x38, 0x18, 0x28, 0x08, 0x30, 0x10, 0x20, 0x00,
  0x7f, 0x3f, 0x5f, 0x1f, 0x6f, 0x2f, 0x4f, 0x0f,
  0x77, 0x37, 0x57, 0x17, 0x67, 0x27, 0x47, 0x07,
  0x7b, 0x3b, 0x5b, 0x1b, 0x6b, 0x2b, 0x4b, 0x0b,
  0x73, 0x33, 0x53, 0x13, 0x63, 0x23, 0x43, 0x03,
  0x7d, 0x3d, 0x5d, 0x1d, 0x6d, 0x2d, 0x4d, 0x0d,
  0x75, 0x35, 0x55, 0x15, 0x65, 0x25, 0x45, 0x05,
  0x79, 0x39, 0x59, 0x19, 0x69, 0x29, 0x49, 0x09,
  0x71, 0x31, 0x51, 0x11, 0x61, 0x21, 0x41, 0x01,
  0x7e, 0x3e, 0x5e, 0x1e, 0x6e, 0x2e, 0x4e, 0x0e,
  0x76, 0x36, 0x56, 0x16, 0x66, 0x26, 0x46, 0x06,
  0x7a, 0x3a, 0x5a, 0x1a, 0x6a, 0x2a, 0x4a, 0x0a,
  0x72, 0x32, 0x52, 0x12, 0x62, 0x22, 0x42, 0x02,
  0x7c, 0x3c, 0x5c, 0x1c, 0x6c, 0x2c, 0x4c, 0x0c,
  0x74, 0x34, 0x54, 0x14, 0x64, 0x24, 0x44, 0x04,
  0x78, 0x38, 0x58, 0x18, 0x68, 0x28, 0x48, 0x08,
  0x70, 0x30, 0x50, 0x10, 0x60, 0x20, 0x40, 0x00,
};

void SDD1::Decomp::GCD::get_run_count(uint8 code_number, uint8 &mps_count, bool &lps_index) {
  uint8 codeword = self.im.get_codeword(code_number);

  if(codeword & 0x80) {
    lps_index = 1;
    mps_count = run_count[codeword >> (code_number ^ 0x07)];
  } else {
    mps_count = 1 << code_number;
  }
}

//bits generator

void SDD1::Decomp::BG::init() {
  mps_count = 0;
  lps_index = 0;
}

uint8 SDD1::Decomp::BG::get_bit(bool &end_of_run) {
  if(!(mps_count || lps_index)) self.gcd.get_run_count(code_number, mps_count, lps_index);

  uint8 bit;
  if(mps_count) {
    bit = 0;
    mps_count--;
  } else {
    bit = 1;
    lps_index = 0;
  }

  end_of_run = !(mps_count || lps_index);
  return bit;
}

//probability estimation module

const SDD1::Decomp::PEM::State SDD1::Decomp::PEM::evolution_table[33] = {
  { 0, 25, 25 },
  { 0,  2,  1 },
  { 0,  3,  1 },
  { 0,  4,  2 },
  { 0,  5,  3 },
  { 1,  6,  4 },
  { 1,  7,  5 },
  { 1,  8,  6 },
  { 1,  9,  7 },
  { 2, 10,  8 },
  { 2, 11,  9 },
  { 2, 12, 10 },
  { 2, 13, 11 },
  { 3, 14, 12 },
  { 3, 15, 13 },
  { 3, 16, 14 },
  { 3, 17, 15 },
  { 4, 18, 16 },
  { 4, 19, 17 },
  { 5, 20, 18 },
  { 5, 21, 19 },
  { 6, 22, 20 },
  { 6, 23, 21 },
  { 7, 24, 22 },
  { 7, 24, 23 },
  { 0, 26,  1 },
  { 1, 27,  2 },
  { 2, 28,  4 },
  { 3, 29,  8 },
  { 4, 30, 12 },
  { 5, 31, 16 },
  { 6, 32, 18 },
  { 7, 24, 22 },
};

void SDD1::Decomp::PEM::init() {
  for(unsigned i = 0; i < 32; i++) {
    context_info[i].status = 0;
    context_info[i].mps = 0;
  }
}

uint8 SDD1::Decomp::PEM::get_bit(uint8 context) {
  ContextInfo &info = context_info[context];
  uint8 current_status = info.status;
  uint8 current_mps = info.mps;
  const State &s = SDD1::Decomp::PEM::evolution_table[current_status];

  uint8 bit;
  bool end_of_run;
  switch(s.code_number) {
  case 0: bit = self.bg0.get_bit(end_of_run); break;
  case 1: bit = self.bg1.get_bit(end_of_run); break;
  case 2: bit = self.bg2.get_bit(end_of_run); break;
  case 3: bit = self.bg3.get_bit(end_of_run); break;
  case 4: bit = self.bg4.get_bit(end_of_run); break;
  case 5: bit = self.bg5.get_bit(end_of_run); break;
  case 6: bit = self.bg6.get_bit(end_of_run); break;
  case 7: bit = self.bg7.get_bit(end_of_run); break;
  }

  if(end_of_run) {
    if(bit) {
      if(!(current_status & 0xfe)) info.mps ^= 0x01;
      info.status = s.next_if_lps;
    } else {
      info.status = s.next_if_mps;
    }
  }

  return bit ^ current_mps;
}

//context model

void SDD1::Decomp::CM::init(unsigned offset) {
  bitplanes_info = self.rom_read(offset) & 0xc0;
  context_bits_info = self.rom_read(offset) & 0x30;
  bit_number = 0;
  for(unsigned i = 0; i < 8; i++) previous_bitplane_bits[i] = 0;
  switch(bitplanes_info) {
  case 0x00: current_bitplane = 1; break;
  case 0x40: current_bitplane = 7; break;
  case 0x80: current_bitplane = 3; break;
  }
}

uint8 SDD1::Decomp::CM::get_bit() {
  switch(bitplanes_info) {
  case 0x00:
    current_bitplane ^= 0x01;
    break;
  case 0x40:
    current_bitplane ^= 0x01;
    if(!(bit_number & 0x7f)) current_bitplane = ((current_bitplane + 2) & 0x07);
    break;
  case 0x80:
    current_bitplane ^= 0x01;
    if(!(bit_number & 0x7f)) current_bitplane ^= 0x02;
    break;
  case 0xc0:
    current_bitplane = bit_number & 0x07;
    break;
  }

  uint16 &context_bits = previous_bitplane_bits[current_bitplane];
  uint8 current_context = (current_bitplane & 0x01) << 4;
  switch(context_bits_info) {
  case 0x00: current_context |= ((context_bits & 0x01c0) >> 5) | (context_bits & 0x0001); break;
  case 0x10: current_context |= ((context_bits & 0x0180) >> 5) | (context_bits & 0x0001); break;
  case 0x20: current_context |= ((context_bits & 0x00c0) >> 5) | (context_bits & 0x0001); break;
  case 0x30: current_context |= ((context_bits & 0x0180) >> 5) | (context_bits & 0x0003); break;
  }

  uint8 bit = self.pem.get_bit(current_context);
  context_bits <<= 1;
  context_bits |= bit;
  bit_number++;
  return bit;
}

//output logic

void SDD1::Decomp::OL::init(unsigned offset) {
  bitplanes_info = self.rom_read(offset) & 0xc0;
  r0 = 0x01;
}

uint8 SDD1::Decomp::OL::decompress() {
  switch(bitplanes_info) {
  case 0x00: case 0x40: case 0x80:
    if(r0 == 0) {
      r0 = ~r0;
      return r2;
    }
    for(r0 = 0x80, r1 = 0, r2 = 0; r0; r0 >>= 1) {
      if(self.cm.get_bit()) r1 |= r0;
      if(self.cm.get_bit()) r2 |= r0;
    }
    return r1;
  case 0xc0:
    for(r0 = 0x01, r1 = 0; r0; r0 <<= 1) {
      if(self.cm.get_bit()) r1 |= r0;
    }
    return r1;
  }
}

//core

void SDD1::Decomp::init(unsigned offset) {
  im.init(offset);
  bg0.init();
  bg1.init();
  bg2.init();
  bg3.init();
  bg4.init();
  bg5.init();
  bg6.init();
  bg7.init();
  pem.init();
  cm.init(offset);
  ol.init(offset);
}

uint8 SDD1::Decomp::read() {
  return ol.decompress();
}

uint8 SDD1::Decomp::rom_read(unsigned offset) {
  return sdd1.rom_read(offset);
}

SDD1::Decomp::Decomp() : im(*this), gcd(*this),
  bg0(*this, 0), bg1(*this, 1), bg2(*this, 2), bg3(*this, 3),
  bg4(*this, 4), bg5(*this, 5), bg6(*this, 6), bg7(*this, 7),
  pem(*this), cm(*this), ol(*this) {
}