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signed int si1, si2, sum;

if ( ((si1^si2) 
   | (((si1^(~(si1^si2) 
     & (1 << (sizeof(int)*CHAR_BIT-1))))+si2)^si2)) >= 0) 
{
   /* handle error condition */
}

sum = si1 + si2;

signed int si1, si2, result;

if (((si1^si2) 
  & (((si1 ^ ((si1^si2) 
    & (1 << (sizeof(int)*CHAR_BIT-1))))-si2)^si2)) < 0) 
{
  /* handle error condition */
}
result = si1 - si2;

signed int si1, si2, result;
static_assert(
  sizeof(long long) >= sizeof(int), 
  "Unable to detect overflow after multiplication"
);

signed long long tmp 
  = (signed long long)si1 * (signed long long)si2;

/*
 * If the product cannot be represented as a 32-bit integer, 
 * handle as an error condition.
 */
if ( (tmp > INT_MAX) || (tmp < INT_MIN) ) {
  /* handle error condition */
}
result = (int)tmp;

int si1, si2, sresult;

if ( (si1 < 0) 
  || (si2 < 0) 
  || (si2 >= sizeof(int)*CHAR_BIT) 
  || si1 > (INT_MAX >> si2) ) 
{
  /* handle error condition */
}
else {
  sresult = si1 << si2;
}