Addressing Modes

MIPS is a load/store architecture, which means that only load and store instructions access memory. Computation instructions operate only on values in registers. The bare machine provides only one memory addressing mode: c(rx), which uses the sum of the immediate (integer) c and the contents of register rx as the address. The virtual machine provides the following addressing modes for load and store instructions:

Format	Address Computation
(register)	contents of register
imm	immediate
imm (register)	immediate + contents of register
symbol	address of symbol
symbol $\pm$ imm	address of symbol $+$ or $-$ immediate
symbol (register)	address of symbol + contents of register
symbol $\pm$ imm (register)	(address of symbol $+$ or $-$ immediate) + contents of register

Most load and store instructions operate only on aligned data. A quantity is aligned if its memory address is a multiple of its size in bytes. Therefore, a halfword object must be stored at even addresses and a full word object must be stored at addresses that are a multiple of 4. However, MIPS provides some instructions for manipulating unaligned data.