MIPS III

MIPS III

MIPS III is a backwards-compatible extension of MIPS II that added support for 64-bit memory addressing and integer operations. The 64-bit data type is called a doubleword, and MIPS III extended the general-purpose registers, HI/LO registers, and program counter to 64 bits to support it. New instructions were added to load and store doublewords, to perform integer addition, subtraction, multiplication, division, and shift operations on them, and to move doubleword between the GPRs and HI/LO registers. For shared-memory multiprocessing, the Load Linked Double Word, and Store Conditional Double Word instructions were added. Existing instructions originally defined to operate on 32-bit words were redefined, where necessary, to sign-extend the 32-bit results to permit words and doublewords to be treated identically by most instructions. Among those instructions redefined was Load Word. In MIPS III it sign-extends words to 64 bits. To complement Load Word, a version that zero-extends was added.