APPENDIX A MIPS III INSTRUCTION SET DETAILS
Preliminary Users Manual S15543EJ1V0UM 565
SWR Store Word Right (1/3) SWR
base

SWR

1 0 1 1 1 0 rt offset

31 26 25 21 20 16 15 0
655 16
Format:
SWR rt, offset (base)
Description:
This instruction can be used with the SWL instruction to store the contents of a register into four consecutive bytes
of memory, when the bytes cross a boundary between two words. SWR stores the register into the appropriate
part of the low-order word; SWL stores the register into the appropriate part of the low-order word of memory.
The SWR instruction adds its sign-extended 16-bit
offset
to the contents of general register
base
to form a virtual
address that may specify an arbitrary byte. It alters only the word in memory that contains that byte. From one to
four bytes will be stored, depending on the starting byte specified.
Conceptually, it starts at the least -significant (rightmost) byte of the register and co pies it to the specified byte in
memory; then copies bytes from register to memory until it reaches the high-order byte of the word in memory.
No address error exceptions due to alignment are possible.
address 4
address 0
memory
7 6 5 4
3 2 1 0
before
after
$24
register

SWR $24, 1 ($0)

A B C D
address 4
address 0
7 6 5 4
B C D 0