New arithmetic logic unit with merged circuitry for comparison, minimum/maximum selection and saturation for signed and unsigned numbers

摘要

A saturation-capable arithmetic logic unit (ALU) includes a general-purpose comparator coupled to receive a data value and a saturation threshold value during a saturation operation. Using the general-purpose comparator of the ALU for saturation minimizes circuit area without adversely affecting microprocessor performance. In an unsigned saturation operation, the data value is replaced with the threshold value when the data value is greater than the threshold value. In a signed saturation operation, positive data values are compared with an upper threshold value and negative data values are compared with a lower threshold value. In this manner, the data value need only be compared to either the upper or lower threshold value, rather than both. If the data value falls outside the bounds set by the upper and lower threshold values, the data value is replaced with the nearest threshold value.