Storage pre-alignment and EBCDIC, ASCII and unicode basic latin conversions for packed decimal data

摘要

A method of pre-aligning data for storage during instruction execution improves performance by eliminating the cycles otherwise required for data alignment. The method can convert data between ASCII and Packed Decimal format, and between Unicode Basic Latin and Packed Decimal format. Conversion to Packed Decimal format is needed for decimal hardware in a microprocessor designed to generate decimal results. Converting from Packed Decimal to ASCII and Unicode Basic Latin is necessary to report Decimal Arithmetic results in a required format for the application program. To further improve performance, all available write ports in the fixed point unit (FXU) are utilized to reduce the number of cycles necessary to store results. To prevent data fetching of the unused destination data from slowing down instruction execution, the destination locations are tested for storage access exceptions, but the data for these operands are not actually fetched. A single read request from the FXU to the operand buffers effectively reads the entire destination address (up to 8 double-words of data) in a single cycle.