International Computers Limited

Fujitsu Services Limited

Kevin Hughes

John Richard Eaton

Martin Pixton

On completion of execution of a current block of instructions, a block completion process searches for potential successor blocks, using block descriptors and egress data structures. For each potential successor block, the process compares a set of entry conditions associated with the block with the exit conditions of the current block and, if a match is found, selects the potential successor block as the current block and executes it. A consistency check is performed, to compare the block identity of the successor block with an expected block identity. Block-following code is selectively planted into translated blocks, to call a successor block directly, by-passing the block completion process. The block-following code is optimised, in that it contains tests for entry conditions only if the results of those tests are not known at the time the block-following code is planted.

Instruction execution mechanism

A computer system in which blocks of source code instructions are translated into blocks of target code instructions and executed. During execution, the system builds up dynamic behavior information about frequency of execution of, and relationships between, the blocks. On the basis of this information, a block coalition mechanism selects blocks, and combines them to form an optimized superblock of target code instructions that is functionally equivalent to the combination of the selected blocks. In this way, the system can start with relatively small, naively translated blocks, and build up larger, more optimized blocks, on the basis of the dynamic behavior of the code.

A method of translating source code instructions into target code instructions is described. Prior to translate time, an existing interpreter is analyzed to identify sequences that implement individual source order code instructions. Sub-sequences within each template that implement predetermined sub-functions are identified and eliminated. The sequences are compiled and stored as templates. For each instruction in an input block of source code instructions, the appropriate template for that source code instruction is selected and appended to an output block of target code instructions. The source code block is then analyzed to determine the net effect of the non-implemented sub-functions, and code is planted in the output block to achieve this net effect.

Instruction translation method

An apparatus for adding two BCD numbers, avoids the need for special adders with detection of carries between BCD digits. First, a sum without carries is generated, by forming the binary sum of the two numbers and an all-sixes pattern, without any carries between BCD digits. Next, a sum with carries is generated, by forming the binary sum of the two numbers and an all-sixes pattern, with carries between BCD digits. A mask pattern is then generated, comprising a six in each BCD digit where the sum without carries is unequal to the sum with carries. A result is then generated by forming the binary sum of the two numbers and the mask pattern, with carries between BCD digits.

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Glossop, United Kingdom

Kevin Hughes