US Patent 7464030 Vector search method

Each of the M basic vectors in a noise code book 260 is multiplied by a factor ±1 in a sign adder 270 and combined in an adder 280 to create 2M noise signed vectors. The characteristic of the binary Gray code is utilized as follows. A change ΔGu obtained between a noise signed vector based on a signed word i of the binary Gray code and a noise sign vector based on a sign word u adjacent to the sign word i and different from the sign word i only in a predetermined bit position v is used in such a manner that a sign word u′ which is next to reverse the bit position v on the Gray code sequence can express a change ΔGu′ from the noise signed vector by utilizing the fact that the sign word u′ differs from the sign word u only in one bit position w excluding the bit position V. Thus, calculation is simplified, increasing the vector search speed.