stswi

Store String Word Immediate

stswi RT, RA, NB

Stores a string of words from general-purpose registers to memory, starting at the address in RA and using an immediate byte count.

Encoding

Binary Layout

31

0:5

RT

6:10

RA

11:15

NB

16:20

725

21:30

/

31

 

Format X-form

Opcode 0x7C0005AA

Extension Base

Operands

• RT
  Start Register
• RA
  Base
• NB
  Byte Count
• RS
  Source General Purpose Register

Example

stswi r3, r4, 4

Related

More in Base

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

Stores NB bytes from a sequence of GPRs beginning at RS to memory starting at address RA, extracting bytes left-to-right and wrapping from R31 back to R0 if necessary. This Base ISA instruction does not affect condition registers and provides a byte-oriented string store capability.

Operation

EA ← RA
reg ← RS
byte_index ← 0
for i ← 0 to (NB - 1) do
  MEM[EA+i : EA+i+7] ← GPRC[reg][(32 - 8*(byte_index+1)) : (31 - 8*byte_index)]
  byte_index ← byte_index + 1
  if byte_index = 4 then
    byte_index ← 0
    reg ← (reg + 1) mod 32
  end if
end for

Programming Note

This instruction is not supported in Little-Endian mode. If it is executed in Little-Endian mode and NB > 0, the system alignment error handler is invoked.