Performing variable and/or bitwise shift operation for a shift instruction that does not provide a variable or bitwise shift option

For a microprocessor that does not allow a variable shift operation for at least one operand size, a method of performing a variable shift operation by simulating a first shift instruction that shifts a first operand by a shift count, the method comprising:

• a) identifying a first shift command;
• b) identifying a second shift command;
• c) computing a mask value, wherein said mask value depends on whether said shift count is less than half of said at least one operand size or said shift count is greater than or equal to half of said at least one operand size;
• d) using said mask value to cause one of said first shift command and said second shift command to produce no shift and to cause an other of said first shift command and said second shift command to shift by a number of units smaller than said shift count.

A computer readable medium storing a computer program for a microprocessor that does not allow a shift operation with a variable shift length for at least one operand size, said computer program for simulating said variable shift operation, said computer program comprising sets of executable instructions for:

• a) performing a first shift instruction;
• b) performing a second shift instruction;
• c) computing a mask value, wherein said mask value depends on whether said variable shift length is less than half of said at least one operand size or said variable shift length is greater than or equal to half of said at least one operand size;
• d) causing one of said first shift instruction and said second shift instruction to produce no shift and an other one of said first shift instruction and said second shift instruction to shift by a number of units smaller than said shift count based on the mask value.