PURPOSE:To decrease the hardware quantity by using a barrel shifter, the 1st and 2nd addition/subtraction units, and a stack which controls the arithmetic operations carried out by both addition/subtraction units. CONSTITUTION:The registers 111 and 121 store two types of variables and the addition/subtraction units 112 and 122 perform the prescribed addition or subtraction. A barrel shifter 113 shifts the contents of the register 121 to the right by an optional even number of digits. A barrel shift 114 multiplies the output of the unit 112 by 1/2 and a shifter 124 doubles the outputs of the unit 122. Then an exponent part computing element 103 controls the shift value of the shifter 113 and the address of a ROM 104 and performs the arithmetic operations of an exponent part. A stack 105 decides the addition or the subtraction that is carried out by both units 112 and 122. Thus it is possible to calculate the arctan (y/x) at a high speed and with high accuracy and to decrease the hardware quantity.
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