int DS = Dis.toInt();
int DS = maskLower16(Dis);
  private final void emitSTDoffset (int RS, int RA, Offset Dis) {    if (!VM.BuildFor64Addr && VM.VerifyAssertions) VM._assert(false);    if (VM.VerifyAssertions) VM._assert(fits(Dis, 16));    int DS = Dis.toInt();    int mi = STDtemplate | RS<<21 | RA<<16 | (DS&0xFFFC);    mIP++;    mc.addInstruction(mi);  }