src/lib/intmath/addsub.c

   1 /* Copyright (c) 2003-2004, Roger Dingledine
   2  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   3  * Copyright (c) 2007-2021, The Tor Project, Inc. */
   4 /* See LICENSE for licensing information */
   5
   6 /**
   7  * \file addsub.c
   8  *
   9  * \brief Helpers for addition and subtraction.
  10  *
  11  * Currently limited to non-wrapping (saturating) addition.
  12  **/
  13
  14 #include "lib/intmath/addsub.h"
  15 #include "lib/cc/compat_compiler.h"
  16
  17 /* Helper: safely add two uint32_t's, capping at UINT32_MAX rather
  18  * than overflow */
  19 uint32_t
  20 tor_add_u32_nowrap(uint32_t a, uint32_t b)
  21 {
  22   /* a+b > UINT32_MAX check, without overflow */
  23   if (PREDICT_UNLIKELY(a > UINT32_MAX - b)) {
  24     return UINT32_MAX;
  25   } else {
  26     return a+b;
  27   }
  28 }