bsnes/bsnes/processor/arm/algorithms.cpp

bool ARM::condition(uint4 condition) {
  switch(condition) {
  case  0: return cpsr().z == 1;                          //EQ (equal)
  case  1: return cpsr().z == 0;                          //NE (not equal)
  case  2: return cpsr().c == 1;                          //CS (carry set)
  case  3: return cpsr().c == 0;                          //CC (carry clear)
  case  4: return cpsr().n == 1;                          //MI (negative)
  case  5: return cpsr().n == 0;                          //PL (positive)
  case  6: return cpsr().v == 1;                          //VS (overflow)
  case  7: return cpsr().v == 0;                          //VC (no overflow)
  case  8: return cpsr().c == 1 && cpsr().z == 0;         //HI (unsigned higher)
  case  9: return cpsr().c == 0 || cpsr().z == 1;         //LS (unsigned lower or same)
  case 10: return cpsr().n == cpsr().v;                   //GE (signed greater than or equal)
  case 11: return cpsr().n != cpsr().v;                   //LT (signed less than)
  case 12: return cpsr().z == 0 && cpsr().n == cpsr().v;  //GT (signed greater than)
  case 13: return cpsr().z == 1 || cpsr().n != cpsr().v;  //LE (signed less than or equal)
  case 14: return true;                                   //AL (always)
  case 15: return false;                                  //NV (never)
  }
}

uint32 ARM::bit(uint32 result) {
  if(cpsr().t || instruction() & (1 << 20)) {
    cpsr().n = result >> 31;
    cpsr().z = result == 0;
    cpsr().c = carryout();
  }
  return result;
}

uint32 ARM::add(uint32 source, uint32 modify, bool carry) {
  uint32 result = source + modify + carry;
  if(cpsr().t || instruction() & (1 << 20)) {
    uint32 overflow = ~(source ^ modify) & (source ^ result);
    cpsr().n = result >> 31;
    cpsr().z = result == 0;
    cpsr().c = (1u << 31) & (overflow ^ source ^ modify ^ result);
    cpsr().v = (1u << 31) & (overflow);
  }
  return result;
}

uint32 ARM::sub(uint32 source, uint32 modify, bool carry) {
  return add(source, ~modify, carry);
}

uint32 ARM::mul(uint32 product, uint32 multiplicand, uint32 multiplier) {
  //Modified Booth Encoding
  bool carry = 0;
  unsigned place = 0;

  do {
    step(1);
    signed factor = (int2)multiplier + carry;

    if(factor == -2) product -= multiplicand << (place + 1);
    if(factor == -1) product -= multiplicand << (place + 0);
    if(factor == +1) product += multiplicand << (place + 0);
    if(factor == +2) product += multiplicand << (place + 1);

    carry = multiplier & 2;
    place += 2;
    multiplier >>= 2;
  } while(multiplier + carry && place < 32);

  if(cpsr().t || instruction() & (1 << 20)) {
    cpsr().n = product >> 31;
    cpsr().z = product == 0;
    cpsr().c = carry;
  }

  return product;
}

uint32 ARM::lsl(uint32 source, uint32 shift) {
  while(shift--) {
    carryout() = source >> 31;
    source <<= 1;
  }

  if(cpsr().t) {
    cpsr().n = source >> 31;
    cpsr().z = source == 0;
    cpsr().c = carryout();
  }

  return source;
}

uint32 ARM::lsr(uint32 source, uint32 shift) {
  while(shift--) {
    carryout() = source & 1;
    source >>= 1;
  }

  if(cpsr().t) {
    cpsr().n = source >> 31;
    cpsr().z = source == 0;
    cpsr().c = carryout();
  }

  return source;
}

uint32 ARM::asr(uint32 source, uint32 shift) {
  while(shift--) {
    carryout() = source & 1;
    source = (int32)source >> 1;
  }

  if(cpsr().t) {
    cpsr().n = source >> 31;
    cpsr().z = source == 0;
    cpsr().c = carryout();
  }

  return source;
}

uint32 ARM::ror(uint32 source, uint32 shift) {
  while(shift--) {
    carryout() = source & 1;
    source = (source << 31) | (source >> 1);
  }

  if(cpsr().t) {
    cpsr().n = source >> 31;
    cpsr().z = source == 0;
    cpsr().c = carryout();
  }

  return source;
}

uint32 ARM::rrx(uint32 source) {
  carryout() = source & 1;
  source = (cpsr().c << 31) | (source >> 1);
}