To provide a function approximation device capable of accurately providing an approximate value of a function value of a curvilinear function by dividing a scope of a variable at points other than points that divide it at equal widths, and approximating the curvilinear function by a plurality of linear functions.
When an addition control signal S1=0, an adder 11 adds zero to X7, and when the addition control signal S1=0, it adds one to X7. An approximate expression parameter table 12 outputs approximate expression parameters a1 and b1, or a2 and b2 corresponding to an output value of the adder 11, and an attribute bit P. A decoder 14 initializes the S1 to zero, and then decodes X6 and P. When P=0, or P=1 and X6=0, the decoder 14 changes S1 to one. A multiplier 15 carries out multiplication of a1 or a2 with X6X5...X0, an adder 16 adds an output of the multiplier to b1 or b2, and (a1x+b1) or {a2(x-128)+b2} is outputted.
NISHI HIDEFUMI
OKA TAKAHIRO
