Power-residue calculating unit and method of controlling the same

1 . A power-residue calculating unit comprising:

a multiplication residue calculating unit performing a multiplication calculation and a residue calculation based on a multiplicand, a multiplier, and a divisor;

a power storing portion separately storing value of each bit when a power is shown by a binary number;

a first selecting circuit outputting one of an output of the multiplication residue calculating unit and the multiplicand depending on the value of the bit that is referred; and

a result storing register storing an output value of the first selecting circuit as a calculation result.

2 . The power-residue calculating unit according to claim 1 , wherein the multiplication residue calculating unit alternately performs a first calculation and a second calculation, the first calculation using the calculation result of a preceding period stored in the result storing register as the multiplicand and the multiplier, and the second calculation using the calculation result of a preceding period stored in the result storing register as the multiplicand and using an input value newly input as the multiplier.

3 . The power-residue calculating unit according to claim 1 , wherein the power-residue calculating unit comprises a control circuit referring to the value of the bit and generating a first selecting signal designating which value the first selecting circuit selects.

4 . The power-residue calculating unit according to claim 3 , wherein the control circuit comprises the power storing portion and a sequence control circuit successively referring to the value of the bit of the power storing portion and outputting the first selecting signal.

5 . The power-residue calculating unit according to claim 3 , wherein the control circuit comprises a storage device functioning as the power storing portion and in which a program is stored, a setting register in which a value of a first reference value referred to as a value of the first selecting signal is stored, and a central processing unit outputting a value stored in the setting register based on the program.

6 . The power-residue calculating unit according to claim 2 , further comprising a second selecting circuit outputting the calculation result of a preceding period to the multiplication residue calculating unit as the multiplier in the first calculation, and outputting the input value to the multiplication residue calculating unit as the multiplier in the second calculation.

7 . The power-residue calculating unit according to claim 6 , further comprising a control circuit generating a second selecting signal designating which value the second selecting circuit selects based on progress information of the calculation.

8 . The power-residue calculating unit according to claim 7 , wherein the control circuit comprises a storage device functioning as the power storing portion and in which a program is stored, a setting register in which a value of a second reference value referred to as a value of the second selecting signal is stored, and a central processing unit outputting a value stored in the setting register based on the program.

9 . The power-residue calculating unit according to claim 1 , further comprising a first intermediate register storing the multiplicand, and a second intermediate register storing the multiplier.

10 . A method of controlling a power-residue calculating unit, the method comprising:

separately storing value of each bit when a power is shown by a binary number;

performing a multiplication calculation and a residue calculation based on a multiplicand, a multiplier, and a divisor; and

storing one of an output of the multiplication residue calculating unit and the multiplicand in a result storing register as a calculation result depending on the value of the bit that is referred.