The n-to-m bit down-scaling correlates a plurality of n-bit correlation
integral values into a plurality of m-bit data (n>m). The n-bit
correlation integral values are obtained by correlating global
positioning system (GPS) signals with a plurality of expected codes.
Upper (n-m+1) bits are selected from the n-bit correlation integral
values, and (n-m+1)-bit estimated absolute values are obtained. A
significant bit of a maximum value of the upper (n-m+1) bits of the
estimated absolute values is selected. A scale level is obtained based on
the significant bit of the maximum value. The n-bit correlation integral
values are down-scaled into the m-bit data based on the scale level. The
amount of n-bit correlation integral values is reduced into m-bit
correlation integral values by the down-scaling method, and thereby
reducing a size of the memory for storing the correlation integral
values.