File::NextCharacter() WIP

gistfile1.cpp

int
File::NextCharacter()
{
  unsigned char b, e, s; /* [0-255], [0-8], [0-8] */
            int c;
        ssize_t i, r;
  
  /*
   * b (Byte)      : Current byte.
   * c (Character) : Current character. (32-bits for Unicode)
   * e (Expected)  : Bytes expected in sequence.
   * i (Index)     : Current index (offset from start of buffer).
   * r (Read)      : Bytes read into buffer.
   * s (Shift)     : Consecutive 1 bits from the highest-order bit.
   */
  
  c = 0;
  e = 0;
  i = (ssize_t) this->mBufferIndex;
  r = (ssize_t) this->mBufferLength;
  
loop:
  if (i >= r) {
    goto read;
  }
  
  b = this->mBuffer[i];
  
  /* Count consecutive 1 bits. */
  for (s = 0; b & 0x80 >> s; s++) {
    if (s > 1 && e > 0) throw SequenceMissingByte();
    if (s > 4)          throw SequenceTooLong();
  }
  
  if (s != 1 && e > 0)  throw SequenceMissingByte();
  
  c <<= 7 - s;
  c  |= b & 0x7F >> s;
  e   = s - 1;
  i  += 1;
  
  if (e > 0) {
    goto loop;
  }
  
  goto done;
  
read: i = 0;
  if (r = read(this->mDescriptor, this->mBuffer, this->mBuffer.Size()), r < 0) {
    switch (errno) {
      case EINTR:
        /* Handle Interupt */
        goto read;
        
      default:
        throw errno;
    }
  }
  
  if (r == 0) {
    if (e == 0) {
      goto done;
    }
    
    throw SequenceMissingByte();
  }
  
  goto loop;
  
done:
  this->mBufferIndex  = (size_t) i;
  this->mBufferLength = (size_t) r; /* TODO: I may need a cast here. */
  
  return c;
}