High-efficiency multiplier and multiplying method

A multiplier comprising:

• two multipliers for executing m (m is a natural number and an even number)/2 bit×n (n is a natural number and an even number)/2 bit multiplication;
• two multiplicand selectors, respectively connected to multiplicand input sides of the two multipliers, for selecting one multiplicand from a plurality of multiplicands;
• two multiplicator selectors, respectively connected to multiplicator input sides of the two multipliers, for selecting one multiplicator from a plurality of multiplicators;
• a connector for connecting two output data from the two multipliers;
• first and second output holding circuits for respectively holding two output data from the two multipliers;
• an adder for adding two data;
• an addition output holding circuit for holding addition result of the adder;
• and
• an addition input selecting circuit for selecting input data to the adder;
• wherein, in order to execute four sets of m/2 bit×n/2 bit multiplication, the two multiplicand selectors select two sets of m/2-bit multiplicands respectively and the two multiplicator selectors select two sets of n/2-bit multiplicators corresponding to the two sets of m/2-bit multiplicands respectively, then the selected two sets of m/2-bit multiplicands and the selected two sets of n/2-bit multiplicators are input into the two multipliers, then two sets of m/2 bit×n/2 bit multiplication are executed in parallel, and then two output data of the two multipliers are held by the first and second output holding circuits respectively, and then
• the two multiplicand selectors select remaining two sets of m/2-bit multiplicands respectively and the two multiplicator selectors select remaining two sets of n/2-bit multiplicators corresponding to the remaining two sets of m/2-bit multiplicands respectively, then the selected remaining two sets of m/2-bit multiplicands and the selected remaining two sets of n/2-bit multiplicators are input into the two multipliers, and then remaining two sets of m/2 bit×n/2 bit multiplication are executed in parallel, and
• wherein, in order to execute m bit×n bit multiplication, a multiplicand selector connected to one multiplier selects an upper m/2-bit multiplicand and a corresponding multiplicator selector selects a lower n/2-bit multiplicator, then a multiplicand selector connected to other multiplier selects an lower m/2-bit multiplicand and a corresponding multiplicator selector selects an upper n/2-bit multiplicator, then the selected m/2-bit multiplicands and the selected n/2-bit multiplicators are input into the two multipliers respectively, then two sets of multiplication of (upper m/2 bits of m bits)×(lower n/2 bits of n bits) and (lower m/2 bits of m bits)×(upper n/2 bits of n bits) are executed in parallel, and then two output data of the two multipliers are held by the first and second output holding circuits respectively, and then
• multiplication results held respectively by the first and second output holding circuits are selected by the addition input selecting circuit and then added by the adder, then added result is held by the addition output holding circuit, and at the same time the multiplicand selector connected to the one multiplier selects the lower m/2-bit multiplicand and the corresponding multiplicator selector selects the lower n/2-bit multiplicator, then the multiplicand selector connected to the other multiplier selects the upper m/2-bit multiplicand and the corresponding multiplicator selector selects the upper n/2-bit multiplicator, then the selected m/2-bit multiplicands and the selected n/2-bit multiplicators are input into the two multipliers respectively, then two sets of multiplication of (lower m/2 bits of m bits)×(lower n/2 bits of n bits) and (upper m/2 bits of m bits)×(upper n/2 bits of n bits) are executed in parallel, and
• two sets of output data held by the first and second output holding circuits are connected by the connector, and
• connected data output from the connector and the added result held by the addition output holding circuit are selected by the addition input selecting circuit, and then added by the adder with arranging in a predetermined bit location each other.