How get two's complement of a register value in ARM?

Question

Say I have a 32 bit signed int in register v1. I want to get the two's complement of this value to store in another register v2. In normal math that means I need to flip all 32 bits and then add 1.

How do I flip the bits?

Answer 1

Try this, (MVN move with not):

MVN v2, v1

This "flips the bits" like you asked. Then you just do the +1:

ADD v2, v1, #1

Alternatively you can just use the NEG v2, v1 instruction (a short-hand for RSB v2, v1, #0) to do the equivalent operation in a single instruction.