Specialized millicode instruction for range checking

摘要

A range check instruction sequence, which performs a logical comparison between two 32-bit values and updates the condition code as a result. It operates identically to the ESA/390 instruction compare logical (CLR) except for the way in which the condition code is set. The new condition code is a function of both the comparison result and the previous condition code. If the first operand is greater than the second operand, the condition code remains unchanged. If the first operand is less than or equal to the second operand, the condition code is set to 2 if it was previously 0 or 1, and is set to 3 if it was previously 2 or 3. This may be understood as advancing the state of the condition code among the groups (0,1), 2, and 3 if the first operand is not greater than the second operand.