A checksum calculator employs a tree structure of reduction stages to process words of a checksum data array. The number of words in the checksum data array is compared to the number of words each of the reduction stages might process. If the number of words in the checksum data array is greater than the number of words that the highest level reduction stage might process, then a portion of the checksum data array is processed, remaining words of the checksum data array are appended to the processed portion, and the process is repeated. If the number of words in the checksum data array is less than or equal to the number of words that the highest level reduction stage might process, then the checksum data array is processed by the lowest level reduction stage that can process the entire checksum data array.