CMN (register-shifted register)

Compare Negative (register-shifted register) adds a register value and a register-shifted register value. It updates the condition flags based on the result, and discards the result.

A1

313029282726252423222120191817161514131211109876543210
!= 111100010111Rn(0)(0)(0)(0)Rs0stype1Rm
cond

Encoding for the A1 variant

CMN{<c>}{<q>} <Rn>, <Rm>, <type> <Rs>

Decode for this encoding

constant n = UInt(Rn); constant m = UInt(Rm); constant s = UInt(Rs); constant shift_t = DecodeRegShift(stype); if n == 15 || m == 15 || s == 15 then UNPREDICTABLE;

For more information about the constrained unpredictable behavior, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<c>

See Standard assembler syntax fields.

<q>

See Standard assembler syntax fields.

<Rn>

Is the first general-purpose source register, encoded in the "Rn" field.

<Rm>

Is the second general-purpose source register, encoded in the "Rm" field.

<type>

Is the type of shift to be applied to the second source register, encoded in stype:

stype <type>
00 LSL
01 LSR
10 ASR
11 ROR
<Rs>

Is the third general-purpose source register holding a shift amount in its bottom 8 bits, encoded in the "Rs" field.

Operation

if ConditionPassed() then EncodingSpecificOperations(); constant shift_n = UInt(R[s]<7:0>); constant shifted = Shift(R[m], shift_t, shift_n, PSTATE.C); constant (result, nzcv) = AddWithCarry(R[n], shifted, '0'); PSTATE.<N,Z,C,V> = nzcv;

Operational information

If CPSR.DIT is 1, this instruction has passed its condition execution check, and does not use R15 as either its source or destination:


Internal version only: isa v01_32, pseudocode v2024-12_rel ; Build timestamp: 2024-12-16T10:54

Copyright © 2010-2024 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.