Look-ahead carry adder circuit

A method of adding two multi-bit addends, the method comprising:

• receiving two multi-bit addends;
• determining a propagate value and a corresponding generate value for each bit of the addends;
• determining a carry-out value for each propagate value based at least in part on the propagate value and corresponding generate value, wherein the carry-out values are determined by a plurality of carry generation blocks, and wherein one of the carry generation blocks determines exactly three of the carry-out values;
• and
• determining a sum value for each carry-out value based at least on part of the carry-out value.

A look-ahead carry adder circuit, comprising:

• inputs to receive two multi-bit addends;
• a plurality of blocks each of which is connected to one input bit of both of the multi-bit addends, wherein each block has a propagate output and a generate output;
• a plurality of carry generation blocks each having inputs connected to two or more of said propagate outputs and two or more of said generate outputs, wherein one of the carry generation blocks is connected to exactly three of the propagate outputs and three of the generate outputs, and wherein each of the carry generation blocks has a plurality of carry outputs;
• and
• a plurality of final blocks each of which is connected to one of said carry outputs and each having a sum output.