cmp

Compare (A32)

CMP<c> <Rn>, <Rm> {, <shift>}

Subtracts two values and updates flags (discarding result).

Pseudocode Operation

if ConditionPassed() then
  (result, carry, overflow) ← AddWithCarry(Rn, NOT(shifted_Rm), '1')
  N ← result[31]
  Z ← (result == 0)
  C ← carry
  V ← overflow

Example

CMP r1, r2

Encoding

Binary Layout

cond

31:28

00010

27:23

22:21

19:16

imm5

11:7

stype

6:5

3:0

Format Data Proc

Opcode 0x01500000

Extension A32 (Base)

Operands

Rn
First source / base general-purpose register
Rm
Second source / offset general-purpose register

Other forms of cmp

cmp Compare (Immediate)

Reference

View in Arm A64 ISA Reference ↗ Arm AArch32 ISA

Instruction Forms

Encoding	Instruction	ISA	Bit pattern
0x03500000	CMP{<c>}{<q>} <Rn>, #<const>	A32	cond \| 00110 \| 10 \| 1 \| Rn \| 0 \| 0 \| 0 \| 0 \| imm12
0x2800	CMP{<c>}{<q>} <Rn>, #<imm8>	T32	001 \| 01 \| Rn \| imm8
0xF1B00F00	CMP{<c>}.W <Rn>, #<const>	T32	11110 \| i \| 0 \| 1101 \| 1 \| Rn \| 0 \| imm3 \| 1111 \| imm8
0x01500060	CMP{<c>}{<q>} <Rn>, <Rm>, RRX	A32	cond \| 00010 \| 10 \| 1 \| Rn \| 0 \| 0 \| 0 \| 0 \| 00000 \| 11 \| 0 \| Rm
0x01500000	CMP{<c>}{<q>} <Rn>, <Rm> {, <shift> #<amount>}	A32	cond \| 00010 \| 10 \| 1 \| Rn \| 0 \| 0 \| 0 \| 0 \| imm5 \| stype \| 0 \| Rm
0x4280	CMP{<c>}{<q>} <Rn>, <Rm>	T32	010000 \| 1010 \| Rm \| Rn
0x4500	CMP{<c>}{<q>} <Rn>, <Rm>	T32	010001 \| 01 \| N \| Rm \| Rn
0xEBB00F30	CMP{<c>}{<q>} <Rn>, <Rm>, RRX	T32	1110101 \| 1101 \| 1 \| Rn \| 0 \| 000 \| 1111 \| 00 \| 11 \| Rm
0xEBB00F00	CMP{<c>}.W <Rn>, <Rm>	T32	1110101 \| 1101 \| 1 \| Rn \| 0 \| imm3 \| 1111 \| imm2 \| stype \| Rm
0x01500010	CMP{<c>}{<q>} <Rn>, <Rm>, <type> <Rs>	A32	cond \| 00010 \| 10 \| 1 \| Rn \| 0 \| 0 \| 0 \| 0 \| Rs \| 0 \| stype \| 1 \| Rm

Description

Compare (register) subtracts an optionally-shifted register value from a register value. It updates the condition flags based on the result, and discards the result.

Operation

if ConditionPassed() then
    EncodingSpecificOperations();
    shifted = Shift(R[m], shift_t, shift_n, PSTATE.C);
    (result, nzcv) = AddWithCarry(R[n], NOT(shifted), '1');
    PSTATE.<N,Z,C,V> = nzcv;

cmp