extsw

Extend Sign Word

extsw RT,RS

Sign extends the low word (32-bit) to 64 bits.

Encoding

Binary Layout

31

0:5

RS

6:10

RA

11:15

986

16:20

/

21:31

 

Format X-form

Opcode 0x7C0007B4

Extension Base

Operands

• RA
  Target
• RS
  Source
• RT
  Target General Purpose Register

Example

extsw r3, r3

Registers Altered

CR0, XER

Related

More in Base

Reference

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

Description

The contents of register RS are extended to fill the upper 32 bits of register RA, and the lower 32 bits of RA are filled with a copy of the upper 32 bits of RS.

Operation

if 'extsw' then
    s ← (RS)32
    RA32:63 ← (RS)32:63
    RA0:31 ← 32s
else if 'extsw.' then
    s ← (RS)32
    RA32:63 ← (RS)32:63
    RA0:31 ← 32s

Programming Note

The extsw instruction is commonly used to sign-extend a 32-bit value in RS to a 64-bit value in RA. Ensure that the source register RS contains the correct 32-bit signed integer to avoid unexpected results. This instruction operates at user privilege level and does not generate exceptions under normal circumstances.