ARM VERSION 1.2 - Manual (Page 144)

ARM Instruction Reference
4-34 Copyright © 2000, 2001 ARM Limited. All rights reserved. ARM DUI 0068B
4.3.5 CMP and CMN
Compare and Compare Negative.
Syntax
CMP{cond} Rn, Operand2
CMN{cond} Rn, Operand2
where:
cond is an optional condition code (see Conditional execution on page 4-4).
Rn is the ARM register holding the first operand.
Operand2 is a flexible second operand. See Flexible second operand on page 4-24
for details of the options.
Usage
These instructions compare the value in a register with Operand2 . They update the
condition flags on the result, but do not place the result in any register.
The CMP instruction subtracts the value of Operand2 from the value in Rn . This is the same
as a SUBS instruction, except that the result is discarded.
The CMN instruction adds the value of Operand2 to the value in Rn . This is the same as an
ADDS instruction, except that the result is discarded.
In certain circumstances, the assembler can substitute CMN for CMP , or CMP for CMN . Be
aware of this when reading disassembly listings. See Instruction substitution on
page 4-26 for details.
Condition flags
These instructions update the N, Z, C and V flags according to the result.
Use of r15
If you use r15 as Rn , the value used is the address of the instruction plus 8.
You cannot use r15 for any operand in any data processing instruction that has a
register-controlled shift (see Flexible second operand on page 4-24).