四步搜索算法对三步算法进行了适当的改进，在一定程度上弥补了TSS算法法在估计细小运动时的不足，并加入了半途中止的策略，进一步提高了搜索精度 -Appropriate improvements to the four-step search algorithm on a three-step algorithm, to a certain extent make up for the deficiencies of the TSS algorithm in estimating the sma