y += x
	return (y-1)&y == 0
}

// bitconEncode returns the encoding of a bitcon used in logical instructions
// x is known to be a bitcon
// a bitcon is a sequence of n ones at low bits (i.e. 1<<n-1), right rotated
// by R bits, and repeated with period of 64, 32, 16, 8, 4, or 2.
// it is encoded in logical instructions with 3 bitfields
// N (1 bit) : R (6 bits) : S (6 bits), where
// N=1           -- period=64