Instruction Syntax

Mnemonic	Format	Flags
beq	target	LK = 0
beql	target	LK = 1

Instruction Encoding

Field	Bits	Description
Primary Opcode	0-5	010010 (0x12)
BO	6-10	01010 (Branch Option)
BI	11-15	00000 (Branch Input - CR0[EQ])
BD	16-29	Branch displacement (14-bit signed)
AA	30	Absolute Address
LK	31	Link bit

Operation

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

BEQ branches to the target address if the Equal (EQ) bit in Condition Register field 0 is set.

1. Checks if the Equal bit (EQ) in CR0 is set
2. If equal, calculates the target address
3. Branches to the target address
4. Optionally saves the return address in LR if LK=1

Note: BEQ is a derived form of the BC (Branch Conditional) instruction with BO=01010 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 Conditional Branch

# Compare two values and branch if equal
cmpw r3, r4           # Compare r3 with r4
beq equal_values      # Branch if r3 == r4
# Continue here if not equal
b continue_code

equal_values:
# Code executed when r3 == r4
continue_code:

Loop Control

# Loop until counter reaches zero
loop_start:
# ... loop body ...
subi r3, r3, 1        # Decrement counter
cmpwi r3, 0           # Compare with zero
beq loop_end          # Branch if counter == 0
b loop_start          # Continue loop

loop_end:

Function Call with Return

# Call function and return if successful
cmpwi r3, 0           # Check return value
beql function_success # Branch and link if equal
# Handle error case
b error_handler

function_success:
# Handle success case
blr                   # Return from function

Array Processing

# Process array until end marker found
process_array:
lwz r4, 0(r3)         # Load array element
cmpwi r4, -1          # Check for end marker
beq array_end         # Branch if end marker found
# Process element
addi r3, r3, 4        # Move to next element
b process_array

array_end:

String Comparison

# Compare strings character by character
string_compare:
lbz r4, 0(r3)         # Load character from string1
lbz r5, 0(r6)         # Load character from string2
cmpw r4, r5           # Compare characters
beq continue_compare  # Branch if characters equal
b strings_different   # Strings are different

continue_compare:
cmpwi r4, 0           # Check for null terminator
beq strings_equal     # Branch if end of string reached
addi r3, r3, 1        # Move to next character
addi r6, r6, 1
b string_compare

Error Handling

# Check for error conditions
cmpwi r3, 0           # Check error code
beq no_error          # Branch if no error (error code == 0)
# Handle error case
b error_handler

no_error:
# Continue normal execution

Related Instructions

bc (Branch Conditional), bne (Branch if Not Equal), bge (Branch if Greater or Equal), blt (Branch if Less Than)