lhax

Load Halfword Algebraic Indexed X-form

lhax RT,RA,RB

Loads a halfword from memory into a register and extends it to a full word, with indexed addressing.

Encoding

Binary Layout

18

0:5

LI

6:29

AA

30

LK

31

 

Format X-form

Opcode 0x7C0002AE

Extension Base

Operands

• RT
  Target General Purpose Register
• RA
  Base General Purpose Register
• RB
  Index General Purpose Register

Example

lhax r3, r4, r5

Related

More in Base

Reference

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

Description

The effective address (EA) is the sum of the contents of registers RA and RB. The halfword in storage addressed by EA is loaded into RT48:63, and RT0:47 are filled with a copy of bit 0 of the loaded halfword.

Operation

if RA = 0 then
    b ← 0
else
    b ← (RA)
EA ← b + (RB)
RT ← EXTS(MEM(EA, 2))

Programming Note

The lhax instruction is commonly used for loading a signed halfword from memory into the upper half of a register. Ensure that RA and RB are correctly set to avoid incorrect effective address calculation. This instruction requires the operands to be properly aligned; accessing unaligned data can lead to exceptions. The result is sign-extended, so be cautious when interpreting the value in RT.