Assembly Language Twos Complement

You can use a Bitwise NOT to flip all of the bits in a register, ie a binary digit of 0 becomes 1 and so on. We can use this to write a program to convert numbers to Two's Complement:

Program

mov r0, #20
mvn r1,r0
add r1,r1,#1

Explanation

Line 1 will get a value from the keyboard, and store it in Register 0.

Line 2 will perform a Bitwise NOT on the value in Register 0, and store it in Register 1.

Line 3 will Add #1 to the value in Register 1, and store it in Register 1.

Line 4 will output the value in Register 1 to the screen.