cmpl
Compare Logical - 7C 00 00 40
cmpl
Instruction Syntax
| Mnemonic | Format | Flags |
| cmpl | crfD,L,rA,rB | - |
| cmplw | crfD,rA,rB | L = 0 (extended mnemonic) |
Instruction Encoding
0
1
1
1
1
1
c
c
c
0
L
A
A
A
A
A
B
B
B
B
B
0
0
0
0
1
0
0
0
0
0
0
| Field | Bits | Description |
| Primary Opcode | 0-5 | 011111 (0x1F) |
| crfD | 6-8 | Condition register field |
| Reserved | 9 | Should be zero |
| L | 10 | 64-bit comparison (0 = 32-bit) |
| rA | 11-15 | Source register A |
| rB | 16-20 | Source register B |
| Reserved | 21 | Should be zero |
| XO | 22-30 | 32 (Extended opcode) |
| Reserved | 31 | Should be zero |
Operation
a ← (rA) b ← (rB) if a u b then c ← 0b010 else c ← 0b001 CR[4×crfD+32:4×crfD+35] ← c || XER[SO]
The contents of rA are compared with the contents of rB treating the operands as unsigned integers. The result of the comparison is placed into condition register field crfD.
Note: In 32-bit implementations, if L=1 the instruction form is invalid.
Affected Registers
Condition Register (crfD field)
(always)
- LT (Less Than) - Set if (rA)
- GT (Greater Than) - Set if (rA) >u (rB) (unsigned)
- EQ (Equal) - Set if (rA) = (rB)
- SO (Summary Overflow) - Copy of XER[SO]
For more information on condition codes see Section 2.1.3, "Condition Register," in the PowerPC Microprocessor Family: The Programming Environments manual.
Examples
Basic Unsigned Comparison
cmpl cr0, 0, r3, r4 # Compare r3 and r4 unsigned, set CR0 cmplw cr1, r5, r6 # Compare r5 and r6 unsigned (32-bit), set CR1
Comparing Addresses/Pointers
cmpl cr0, 0, r3, r4 # Compare two addresses blt lower_address # Branch if r3 < r4 (unsigned) beq same_address # Branch if addresses are equal bgt higher_address # Branch if r3 > r4 (unsigned)
Range Checking for Unsigned Values
# Check if unsigned value is within bounds cmpl cr0, 0, r3, r4 # Compare with lower bound blt out_of_range # Branch if below range cmpl cr0, 0, r3, r5 # Compare with upper bound bgt out_of_range # Branch if above range # Value is within range
Array Index Validation
# Validate array index (unsigned) cmpl cr0, 0, r3, r4 # Compare index with array size bge bounds_error # Branch if index >= size # Index is valid (0 <= index < size)
Memory Address Comparison
# Compare memory addresses for sorting cmpl cr0, 0, r10, r11 # Compare two pointers blt ptr1_lower # r10 points to lower address beq same_location # Both point to same location bgt ptr1_higher # r10 points to higher address
Unsigned Arithmetic Overflow Check
# Check for unsigned addition overflow add r5, r3, r4 # Add two unsigned values cmpl cr0, 0, r5, r3 # Compare result with first operand blt overflow_detected # If result < operand, overflow occurred