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Architecture
190
SWR Store Word Right SWR
31 26 25 21 20 16 15 0
SWR
101110
base rt offset
6 5 5 16
Format :
SWR rt, offset(base)
Description :
Used together with SWL to store the contents of a register into four consecutive bytes of memory
when the bytes cross a word boundary. SWR stores the right part of the register into the
appropriate part of the low-order word in memory; SWL stores the left part of the register into the
appropriate part of the high-order word in memory.
This instruction generates a 32-bit effective address that can point to any byte by sign-extending the
16-bit offset and adding it to the contents of general-purpose register base. Only the one word in
memory containing the designated starting byte is modified. Depending on the starting byte, from
one to four bytes are stored.
The concept is illustrated below. This instruction (SWR) starts from the low-order (right-most)
byte of the register and stores it into the designated memory byte; it then continues storing bytes
from register to memory, proceeding toward the high-order byte of the register and the high-order
byte of the memory word, until it reaches the high-order byte of the memory word.
No Address Error instruction is raised due to misalignment.
Memory
(Big endian)
Before
storing
SWR $24,4($0)
After
storing
Address 4 D 5 6 7
Address 0 0 1 2 3
Address 4 4 5 6 7
Address 0 0 1 2 3
Register
A B C D $24