mcrf
Move Condition Register Field - 4C 00 00 00
mcrf
Instruction Syntax
| Mnemonic | Format | Flags |
| mcrf | crfD,crfS | None |
Instruction Encoding
0
1
1
1
1
1
D
D
D
0
0
S
S
S
0
0
0
0
0
0
0
0
0
0
1
0
1
0
0
0
0
0
0
0
0
| Field | Bits | Description |
| Primary Opcode | 0-5 | 011111 (0x1F) |
| crfD | 6-8 | Destination condition register field |
| Reserved | 9-10 | Should be zero |
| crfS | 11-13 | Source condition register field |
| Reserved | 14-20 | Should be zero |
| XO | 21-30 | 0x0A0 (160) - Extended opcode |
| Reserved | 31 | Should be zero |
Operation
CR[4×crfD:4×crfD+3] ← CR[4×crfS:4×crfS+3]
The contents of condition register field crfS are copied to condition register field crfD. Each condition register field contains 4 bits representing the condition codes (LT, GT, EQ, SO).
Note: This instruction allows for efficient manipulation of condition codes without requiring additional comparison operations. It's particularly useful in complex conditional logic where condition codes need to be preserved or transferred between different contexts.
Affected Registers
Condition Register (CR)
(always)
- CR[crfD] - Destination condition register field (LT, GT, EQ, SO bits)
- CR[crfS] - Source condition register field (read only)
For more information on condition codes see Section 2.1.3, "Condition Register," in the PowerPC Microprocessor Family: The Programming Environments manual.
Examples
Basic Condition Field Copy
# Copy condition codes from CR0 to CR1 cmpwi cr0, r3, 0 # Compare r3 with 0, set CR0 mcrf cr1, cr0 # Copy CR0 to CR1
Preserve Condition Codes
# Save condition codes before another comparison cmpwi cr0, r4, 10 # Compare r4 with 10, set CR0 mcrf cr7, cr0 # Save result in CR7 cmpwi cr0, r5, 20 # New comparison overwrites CR0 # CR7 still contains result of r4 comparison
Multiple Condition Tracking
# Track multiple comparison results cmpwi cr0, r3, 0 # Check if r3 is zero mcrf cr1, cr0 # Save zero check result cmpwi cr0, r4, 100 # Check if r4 is 100 mcrf cr2, cr0 # Save range check result cmpwi cr0, r5, -50 # Check if r5 is negative mcrf cr3, cr0 # Save sign check result
Complex Conditional Logic
# Implement complex conditional logic cmpwi cr0, r3, 0 # Check first condition mcrf cr1, cr0 # Save first condition cmpwi cr0, r4, 0 # Check second condition mcrf cr2, cr0 # Save second condition cmpwi cr0, r5, 0 # Check third condition mcrf cr3, cr0 # Save third condition # Now can use all three conditions independently bt cr1, first_true # Branch if first condition true bt cr2, second_true # Branch if second condition true bt cr3, third_true # Branch if third condition true
Function Return Value Checking
# Check multiple function return values bl function1 # Call first function cmpwi cr0, r3, 0 # Check return value mcrf cr1, cr0 # Save function1 result bl function2 # Call second function cmpwi cr0, r3, 0 # Check return value mcrf cr2, cr0 # Save function2 result # Check both results bt cr1, func1_success # Branch if function1 succeeded bt cr2, func2_success # Branch if function2 succeeded
Loop Condition Preservation
# Preserve loop condition for nested logic
loop_start:
cmpwi cr0, r4, 0 # Check loop condition
mcrf cr7, cr0 # Save loop condition
beq cr0, loop_end # Exit if done
# Nested condition that might overwrite CR0
cmpwi cr0, r5, 10 # Some other comparison
bt cr0, do_something
# Restore loop condition
mcrf cr0, cr7 # Restore original loop condition
b loop_start # Continue loop
Error Condition Tracking
# Track multiple error conditions cmpwi cr0, r3, -1 # Check for error code -1 mcrf cr1, cr0 # Save error -1 condition cmpwi cr0, r4, -2 # Check for error code -2 mcrf cr2, cr0 # Save error -2 condition cmpwi cr0, r5, -3 # Check for error code -3 mcrf cr3, cr0 # Save error -3 condition # Handle different error types beq cr1, handle_error1 # Handle error -1 beq cr2, handle_error2 # Handle error -2 beq cr3, handle_error3 # Handle error -3
Range Checking
# Check if value is in multiple ranges cmpwi cr0, r3, 0 # Check if >= 0 mcrf cr1, cr0 # Save >= 0 result cmpwi cr0, r3, 100 # Check if <= 100 mcrf cr2, cr0 # Save <= 100 result cmpwi cr0, r3, 50 # Check if == 50 mcrf cr3, cr0 # Save == 50 result # Use range information bt cr1, positive_value # Branch if >= 0 bt cr2, in_range # Branch if <= 100 beq cr3, exact_50 # Branch if == 50
Status Flag Management
# Manage multiple status flags cmpwi cr0, r3, 0 # Zero flag cmpwi cr1, r4, 0 # Overflow flag cmpwi cr2, r5, 0 # Error flag cmpwi cr3, r6, 0 # Ready flag # Check status combinations bt cr0, zero_detected # Handle zero condition bt cr1, overflow_detected # Handle overflow bt cr2, error_detected # Handle error bt cr3, ready_detected # Handle ready condition
Condition Code Restoration
# Restore condition codes after function call cmpwi cr0, r3, 0 # Set up condition codes mcrf cr7, cr0 # Save them before function call bl some_function # Function call (might modify CR0) mcrf cr0, cr7 # Restore original condition codes beq cr0, original_true # Use restored condition