ARM VERSION 1.2 - page 210

Thumb Instruction Referenc e
5-16 Copyright © 2000, 2001 ARM Limited. A ll 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 .