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#include <assert.h>
#include <limits.h>

#define UWIDTH(type, umax_value) (sizeof(type) * CHAR_BIT)
  
void func(signed int si_a, signed int si_b) {
  signed int result;
  signed long long tmp;
  assert(UWIDTH(signed long long, ULLONG_MAX) >=
         2 * UWIDTH(int, UINT_MAX));
 
  tmp = (signed long long)si_a * (signed long long)si_b;
 
  /*
   * 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 */
  } else {
    result = (int)tmp;
  }
  /* ... */
}

#include <limits.h>

#define UWIDTH(type, umax_value) (sizeof(type) * CHAR_BIT) 

void func(signed long si_a, signed long si_b) {
  signed long result;
  if ((si_a < 0) || (si_b < 0) ||
      (si_b >= UWIDTH(signed long, ULONG_MAX)) ||
      (si_a > (LONG_MAX >> si_b))) {
    /* Handle error */
  } else {
    result = si1 << si2;
  }
 
  /* ... */
}