Instruction Syntax

Mnemonic	Format	Flags
blt	target	LK = 0
bltl	target	LK = 1

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	010010 (0x12)
BO	6-10	01100 (Branch Option)
BI	11-15	00000 (Branch Input - CR0[LT])
BD	16-29	Branch displacement (14-bit signed)
AA	30	Absolute Address
LK	31	Link bit

Operation

if CR0[LT] = 1 then
    if AA = 0 then
        NIA ← CIA + EXTS(BD || 0b00)
    else
        NIA ← EXTS(BD || 0b00)
if LK = 1 then
    LR ← CIA + 4

BLT branches to the target address if the Less Than (LT) bit in Condition Register field 0 is set.

1. Checks if the Less Than bit (LT) in CR0 is set
2. If LT is set (less than), calculates the target address
3. Branches to the target address
4. Optionally saves the return address in LR if LK=1

Note: BLT is a derived form of the BC (Branch Conditional) instruction with BO=01100 and BI=00000.

Affected Registers

Link Register (LR)

(if LK = 1)

• LR - Set to CIA + 4 (return address)

Next Instruction Address (NIA)

• NIA - Set to target address if condition is met

Examples

Basic Less Than Branch

# Compare two values and branch if less than
cmpw r3, r4           # Compare r3 with r4
blt less_than         # Branch if r3 < r4
# Continue here if r3 >= r4
b continue_code

less_than:
# Code executed when r3 < r4
continue_code:

Range Checking

# Check if value is below maximum
cmpwi r3, 100         # Compare with maximum value
blt valid_range       # Branch if r3 < 100
# Handle invalid case (too large)
b error_handler

valid_range:
# Process valid value
# ... processing ...

Array Bounds Checking

# Check array index bounds
cmpwi r3, 0           # Check lower bound
blt invalid_index     # Branch if index < 0
cmpwi r3, 100         # Check upper bound
bge invalid_index     # Branch if index >= 100
# Index is valid, continue processing

Loop Control

# Loop while counter < limit
loop_start:
# ... loop body ...
addi r3, r3, 1        # Increment counter
cmpwi r3, 10          # Compare with limit
blt loop_start        # Continue loop if counter < 10
# Loop finished

Threshold Testing

# Check if value is below threshold
cmpwi r3, 1000        # Compare with threshold
blt below_threshold   # Branch if value < threshold
# Handle above threshold case
b above_threshold

below_threshold:
# Handle below threshold case

Signed Comparison

# Compare signed values
cmpw r3, r4           # Compare r3 with r4 (signed)
blt r3_less           # Branch if r3 < r4
# r3 is greater than or equal to r4
b r3_greater_equal

r3_less:
# r3 is less than r4

Error Condition Checking

# Check for error conditions
cmpwi r3, 0           # Check if value is negative
blt error_negative    # Branch if value < 0
# Continue normal processing
b normal_processing

error_negative:
# Handle negative value error

Related Instructions

bc (Branch Conditional), bge (Branch if Greater or Equal), beq (Branch if Equal), bne (Branch if Not Equal)