protected static int makeByte(int low, int high) {
    if ((low & 0xf) != low) {
      throw new IllegalArgumentException("low out of range 0..15");
    }

    if ((high & 0xf) != high) {
      throw new IllegalArgumentException("high out of range 0..15");
    }

    return low | (high << 4);
  }
Helper method to combine two nibbles into a byte.

@param low {@code 0..15;} low nibble
@param high {@code 0..15;} high nibble
@return {@code 0..255;} combined value
android/android_framework/dex-maker/src/main/java/com/android/dx/dex/code/InsnFormat.java