lwz

Load Word and Zero

lwz RT, D(RA)

Loads a word (32 bits) from memory and clears the upper 32 bits.

Encoding

Binary Layout

32

0:5

RT

6:10

RA

11:15

D

16:31

 

Format D-form

Opcode 0x80000000

Extension Base

Operands

• RT
  Target Register
• D
  Displacement
• RA
  Base Register

Example

lwz r3, 8(r4)

// Load 32-bit int from r4+8.

Related

Across architectures

Load-Acquire : how x86, ARM, RISC-V, and PowerISA each do this.

More in Base

Reference

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

Description

The effective address (EA) is calculated as (RA|0) + EXTS64(D). The word in storage addressed by EA is loaded into RT32:63. RT0:31 are set to 0.

Operation

EA ← (RA|0) + EXTS64(D)
RT ← 320 || MEM(EA, 4)

Programming Note

The lwz instruction is commonly used for loading a word from memory into a register while zeroing the upper half of the target register. Ensure that the address is properly aligned to avoid alignment exceptions. This instruction operates at user privilege level and does not generate any exceptions under normal circumstances.