I'm supposed to change a 16 bit value from positive to negative. After Googling for some minutes I found a solution, but I'm still not sure if it's the right one, so would be great if you could help me. Appreciated!
eor r4, r1, #0x80000000
Use the reverse subtract instruction rsb to perform the task.
rsb r4, r1, #0 @ computes r4 = 0 - r1
This instruction is available both in ARM and in Thumb state, though Thumb1 only has
rsbs Rd, Rn, #0
restricting the immediate operand to #0.