PROBLEM TO BE SOLVED: To improve the efficiency of generating and storing the trace-back bits of a pair corresponding to a surviving branch by selecting two intermediate extremes from generated four metrics and selecting an extreme from the two intermediate extremes. ;SOLUTION: First, second, third and fourth metrics are generated. An arithmetic and logic unit 26 respectively compares the first and second metrics and the third and fourth metrics. A multiplexer 38 selects one of compared results as a first intermediate extreme and a second intermediate extreme and stores it inside a register. Similarly, the first and second intermediate extremes are compared in the arithmetic and logic unit 26, and one of them is selected as the extreme in the multiplexer 38, supplied to a register file 24 and stored inside the register. By performing design so as to utilize pipeline constitution, the efficiency of calculation is improved, as well and the utilization efficiency of the resources of an adder or the like is maximized.;COPYRIGHT: (C)1999,JPO
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