An alternative method for subtracting two 32-bit signed integers in a two's complement system.

alt_subtract.c

/**
 * Performs the subtraction p - q.
 * This is an alternative method to simply computing p + (-q).
 * TODO I'll prove why it works later.
 */
int alt_subtract(int p, int q) {
  // First, take the ones' complement of the minuend
  int p1 = ~p;
  // Next, add the subtrahend
  int sum = p1 + q;
  // The ones' complement of this sum is the difference p - q
  return ~sum;
}

/**
 * Copyright (C) 2017 Aidan Fitzgerald
 * 
 * By themselves, the four lines of code may be ineligible for copyright. However, I claim that the 
 * combination of instructions, choice of variable and function names, and comments is copyrightable.
 * (To be fair, most of the comment prose is this copyright notice.)
 * 
 * To the extent that this work is copyrightable, I hereby release it under the MIT License, available here:
 * https://opensource.org/licenses/MIT
 */