ARM VERSION 1.2 - Manual (Page 210)

Thumb Instruction Reference
5-16 Copyright © 2000, 2001 ARM Limited. All rights reserved. ARM DUI 0068B
5.2.1 ADD and SUB, low registers
Add and subtract. There are three forms of these instructions that operate on low
registers. You can:
• add or subtract the contents of two registers, and place the result in a third register
• add a small integer to, or subtract it from, the value in a register, and place the
result in a different register
• add a larger integer to, or subtract it from, the value in a register, and return the
result to the same register.
Syntax
op Rd, Rn, Rm
op Rd, Rn, #expr3
op Rd, #expr8
where:
op is either ADD or SUB .
Rd is the destination register. It is also used for the first operand in op
Rd,#expr8 instructions.
Rn is a register containing the first operand.
Rm is a register containing the second operand.
expr3 is an expression evaluating (at assembly time) to an integer in the range
–7 to +7.
expr8 is an expression evaluating (at assembly time) to an integer in the range
–255 to +255.
Usage
op Rd,Rn,Rm performs an Rn + Rm or an Rn – Rm operation, and places the result in Rd .
op Rd,Rn,#expr3 performs an Rn + expr3 or an Rn – expr3 operation, and places the result
in Rd .
op Rd,#expr8 performs an Rd + expr8 or an Rd – expr8 operation, and places the result in
Rd .