Double precision approximate quotient network

Apparatus for determining a 2n bit approximate quotient of a 2n bit dividend and a 2n bit divisor comprising:

• means for deriving a first number equal to 2 times 2.sup.n-1 (2.sup.n-1 -1) divided by the n most significant bits of said divisor;
• first multiplier means for multiplying said divisor by said first number to derive a result;
• first complement means for determining the 2's complement of the result from said first multiplier means;
• second multiplier means for multiplying said dividend by said first number to derive a result;
• second complement means for determining the 2's complement of the n most significant bits of the result from said second multiplier means;
• determine means for determining 2 times the 2's complement of the n most significant bits of the result from said second multiplier means;
• select means responsive to the n most significant bits of the 2's complement from said first complement means for selecting a value equal to one of (a) the 2's complement from said second complement means, (b) the 2's complement from said determine means, (c) zero, or (d) the n most significant bits of the result from said second multiplier means;
• shift means for right shifting the result from said second multiplier means one place;
• third multiplier means for multiplying the n most significant bits of the result from said second multiplier means by the n least significant bits of the 2's complement from said first complement means to derive a result;
• and
• adder means for adding the result from said third multiplier means and the result of right shifting by said shift means and the value selected by said select means to determine a 2n bit approximate quotient.

The method of determining a 2n bit partial product of a first 2n bit number and a second n bit number, said n bit number having a value equal to one of (2.sup.n-1 -2), (2.sup.n-1 -1), (2.sup.n-1) and (2.sup.n-1 +1), said method comprising:

• right shifting said first number by one bit to derive a fourth number having a value of either one-half of said first number or one-half of said first number means;
• determining a third number comprising the n most significant bits of said first number;
• multiplying said third number by 2 to achieve a value of twice said third number;
• determining the value of said second number;
• and performing one of the following operations:
• (a) subtracting twice said third number from said fourth number if the value of said second number is 2.sup.n-1 -2,
• (b) subtracting said third number from said fourth number if the value of said second number is 2.sup.n-1 -1,
• (c) selecting said fourth number if said the value of said second number is 2.sup.n-1, or
• (d) adding said third number to said fourth number if the value of said second number is 2.sup.n-1 +1.