static int readCompressed30BitUint_IByteMemory64(IByteMemory64 mem, long ptr) {
  int i = ubyteToInt(mem.getByte(ptr));
  if (i < 0x40) ret i;
  int j = ubyteToInt(mem.getByte(++ptr));
  if (i < 0x80)
    ret ((i & 0x3F) << 8) | j;
  int k = ubyteToInt(mem.getByte(++ptr));
  if (i < 0xC0)
    ret ((i & 0x3F) << 16)
      | (j << 8) | k;
  ret ((i & 0x3F) << 24)
    | (j << 16) | (k << 8) | ubyteToInt(mem.getByte(++ptr));
}

Began life as a copy of #1029524