Decimal multiplication via carry-save addition

Abstract

Decimal multiplication is important in many commercial applications including financial analysis, banking, tax calculation, currency conversion, insurance, and accounting. We present two novel designs for fixed-point decimal multiplication that utilize decimal carry-save addition to reduce the critical path delay. First, a multiplier that stores a reduced number of multiplicand multiples and uses decimal carry-save addition in the iterative portion of the design is presented. Then, a second multiplier design is proposed with several notable improvements including fast generation of multiplicand multiples that do not need to be stored, the use of decimal (4:2) compressors, and a simplified decimal carry-propagate addition to produce the final product. When multiplying two n-digit operands to produce a 2n-digit product, the improved multiplier design has a worst-case latency of n+4 cycles and an initiation interval of n+1 cycles. Three data-dependent optimizations, which help reduce the multipliers' average latency, are also described. The multipliers presented can be extended to support decimal floating-point multiplication.