lbz
Load Byte and Zero - 88 00 00 00
lbz
Instruction Syntax
| Mnemonic | Format | Flags |
| lbz | rD,d(rA) | - |
Instruction Encoding
1
0
0
0
1
0
D
D
D
D
D
A
A
A
A
A
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
d
| Field | Bits | Description |
| Primary Opcode | 0-5 | 100010 (0x22) |
| rD | 6-10 | Destination register |
| rA | 11-15 | Source register A |
| d | 16-31 | 16-bit signed displacement |
Operation
if rA = 0 then EA ← EXTS(d) else EA ← (rA) + EXTS(d) rD ← 0x00 || MEM(EA, 1)
A byte is loaded from memory and placed in the low-order 8 bits of register rD. The upper 24 bits of rD are set to zero. The effective address is computed by adding the sign-extended displacement to the contents of register rA, or zero if rA is 0.
Note: This instruction loads an 8-bit value from memory and zero-extends it to 32 bits. The effective address calculation treats rA=0 as the value 0, not register r0.
Affected Registers
None - This instruction does not affect any condition register fields or XER register bits.
For more information on memory addressing see Section 2.1.6, "Effective Address Calculation," in the PowerPC Microprocessor Family: The Programming Environments manual.
Examples
Basic Byte Loading
lbz r3, 0(r1) # Load byte from address in r1 lbz r4, 100(r2) # Load byte from address r2+100 lbz r5, -50(r3) # Load byte from address r3-50
Loading from Absolute Address
lbz r3, 0x1000(r0) # Load byte from absolute address 0x1000 # Note: r0 treated as value 0, not register contents
Character String Processing
# Process null-terminated string
lis r3, string_ptr@ha
addi r3, r3, string_ptr@l
li r4, 0 # Character index
string_loop:
lbz r5, 0(r3) # Load current character
cmpwi r5, 0 # Check for null terminator
beq string_done # Branch if end of string
# Process character in r5
bl process_char
addi r3, r3, 1 # Move to next character
addi r4, r4, 1 # Increment count
b string_loop
string_done:
Byte Array Access
# Access elements in byte array lis r3, byte_array@ha addi r3, r3, byte_array@l li r4, 5 # Array index lbz r5, 0(r3, r4) # Would use lbzx for indexed access # Instead use displacement: add r6, r3, r4 # Calculate address lbz r7, 0(r6) # Load array[5]
Loading Configuration Bytes
# Load device configuration bytes lis r3, config_base@ha addi r3, r3, config_base@l lbz r4, 0(r3) # Load config byte 0 lbz r5, 1(r3) # Load config byte 1 lbz r6, 2(r3) # Load config byte 2 lbz r7, 3(r3) # Load config byte 3 # Combine into word (big-endian) slwi r4, r4, 24 # Shift byte 0 to bits 0-7 slwi r5, r5, 16 # Shift byte 1 to bits 8-15 slwi r6, r6, 8 # Shift byte 2 to bits 16-23 or r8, r4, r5 # Combine bytes 0,1 or r8, r8, r6 # Add byte 2 or r8, r8, r7 # Add byte 3 - r8 now has full word
Status Register Reading
# Read device status registers lis r3, device_base@ha addi r3, r3, device_base@l lbz r4, STATUS_REG(r3) # Load status byte andi. r5, r4, 0x80 # Check bit 7 (ready flag) beq device_not_ready # Branch if not ready andi. r5, r4, 0x40 # Check bit 6 (error flag) bne device_error # Branch if error # Device ready and no error lbz r6, DATA_REG(r3) # Load data byte
Bitmap Font Character Loading
# Load bitmap font character data lis r3, font_data@ha addi r3, r3, font_data@l li r4, 'A' # Character to load li r5, 8 # 8 bytes per character mullw r6, r4, r5 # Calculate offset add r7, r3, r6 # Character data address # Load 8 bytes of character bitmap lbz r8, 0(r7) # Row 0 lbz r9, 1(r7) # Row 1 lbz r10, 2(r7) # Row 2 lbz r11, 3(r7) # Row 3 lbz r12, 4(r7) # Row 4 lbz r13, 5(r7) # Row 5 lbz r14, 6(r7) # Row 6 lbz r15, 7(r7) # Row 7
Network Packet Header Parsing
# Parse network packet header bytes lis r3, packet_buffer@ha addi r3, r3, packet_buffer@l lbz r4, 0(r3) # Load version/header length lbz r5, 1(r3) # Load type of service lbz r6, 2(r3) # Load total length high byte lbz r7, 3(r3) # Load total length low byte # Extract header length (lower 4 bits of first byte) andi. r8, r4, 0x0F # Header length in 32-bit words slwi r8, r8, 2 # Convert to bytes # Combine total length slwi r6, r6, 8 # High byte to upper position or r9, r6, r7 # Combine high and low bytes
Game State Loading
# Load game state from save data lis r3, save_data@ha addi r3, r3, save_data@l lbz r4, PLAYER_LEVEL(r3) # Load player level lbz r5, PLAYER_HEALTH(r3) # Load health percentage lbz r6, PLAYER_MANA(r3) # Load mana percentage lbz r7, CURRENT_WORLD(r3) # Load world number lbz r8, CURRENT_STAGE(r3) # Load stage number # Validate loaded values cmpwi r4, 99 # Check max level bgt invalid_save # Invalid if > 99 cmpwi r5, 100 # Check max health bgt invalid_save # Invalid if > 100
Color Component Extraction
# Extract RGB components from 32-bit color value # Assuming color stored as 4 bytes: A, R, G, B lis r3, color_buffer@ha addi r3, r3, color_buffer@l lbz r4, 0(r3) # Load alpha component lbz r5, 1(r3) # Load red component lbz r6, 2(r3) # Load green component lbz r7, 3(r3) # Load blue component # Apply alpha blending calculation # NewColor = (SourceColor * Alpha + DestColor * (255 - Alpha)) / 255 li r8, 255 sub r9, r8, r4 # 255 - Alpha mullw r10, r5, r4 # Red * Alpha mullw r11, r6, r4 # Green * Alpha mullw r12, r7, r4 # Blue * Alpha
MIDI Data Parsing
# Parse MIDI message bytes
lis r3, midi_buffer@ha
addi r3, r3, midi_buffer@l
lbz r4, 0(r3) # Load status byte
andi. r5, r4, 0x80 # Check if status byte (bit 7 set)
beq data_byte # Branch if data byte
# Parse status byte
andi. r6, r4, 0xF0 # Extract command nibble
cmpi cr0, 0, r6, 0x90 # Check for note on
beq note_on_msg
cmpi cr0, 0, r6, 0x80 # Check for note off
beq note_off_msg
note_on_msg:
lbz r7, 1(r3) # Load note number
lbz r8, 2(r3) # Load velocity
b process_note_on
note_off_msg:
lbz r7, 1(r3) # Load note number
lbz r8, 2(r3) # Load velocity (usually 0)
b process_note_off
data_byte:
# Handle running status
mr r7, r4 # First data byte
lbz r8, 1(r3) # Second data byte