A controller to control a memory system including a memory device. The controlling the memory system may include calculating an error location polynomial in a received read vector with a key equation solving unit of the memory system to read data from the memory device, estimating the number of errors in the received read vector with a control unit of the memory system according to at least one of the calculated error location polynomial and information on the error location polynomial, searching error locations of the received read vector according to the calculated error location polynomial with a chien search unit of the memory system with the control unit. A cycle-per power consumption of the chien search unit may be adjusted with the control unit. A maximum correction time may be adjusted according to the number of errors of the read vector.