A virtual address is said to be "sign-extended at step 550 when it is modified such that bits n through (m-1) of the virtual address are equal to the value of bit (n-1) of the virtual address, where m is the length of the virtual address and n is a number of bits within the virtual address format used to map the virtual address to physical memory, for example as bits 0 through 42 are used in FIG.