Instruction Syntax

Mnemonic	Format	Flags
stswx	rS,rA,rB	None

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	011111 (0x1F)
rS	6-10	Starting source register
rA	11-15	Base register
rB	16-20	Index register (contains byte count)
Reserved	21-29	000000000
Reserved	30-31	00

Operation

EA ← (rA) + (rB)
NB ← (rB)[0:31]
for i = 0 to NB-1 do
    if i mod 4 = 0 then
        r ← (rS + i/4)
    endif
    (EA + i) ← (r)[(3 - (i mod 4)) * 8 : (3 - (i mod 4)) * 8 + 7]
endfor

The effective address is calculated by adding the base register to the index register. The number of bytes to store (NB) is taken from the index register. Starting from register rS, NB bytes are stored to consecutive memory locations starting at the effective address.

Note: The stswx instruction stores a string of bytes to memory from consecutive registers, with the byte count specified in a register. This is useful for copying data structures or strings of variable length.

Affected Registers

Memory

• NB bytes starting at effective address (EA)
• NB is the value in rB

Examples

Basic Store String Word Indexed

# Store bytes from r3 with count in r4 to address in r5
stswx r3, r5, r4    # Store (r4) bytes starting at r5

Copy Variable Length Data

# Copy data with variable length
li r3, source_data  # Load source data in registers
li r4, 12           # Load byte count
li r5, dest_addr    # Load destination address
stswx r3, r5, r4    # Copy 12 bytes to destination

String Copy with Length

# Copy string with length in register
li r3, string_data  # Load string data in registers
li r4, string_len   # Load string length
li r5, buffer       # Load buffer address
stswx r3, r5, r4    # Copy string to buffer

Related Instructions

stswi, lswx, lswi