static int readCompressed30BitUint(IF0_Byte readByte) {
  int i = ubyteToInt(readByte!);
  if (i < 0x40) ret i;
  if (i < 0x80)
    ret ((i & 0x3F) << 8) | ubyteToInt(readByte!);
  int j = ubyteToInt(readByte!);
  if (i < 0xC0)
    ret ((i & 0x3F) << 16)
      | (j << 8) | ubyteToInt(readByte!);
  int k = ubyteToInt(readByte!);
    ret ((i & 0x3F) << 24)
      | (j << 16) | (k << 8) | ubyteToInt(readByte!);
}

Began life as a copy of #1029522