toplev.c

#if GCC_VERSION < 3004

/* Given X, an unsigned number, return the largest int Y such that 2**Y <= X.
   If X is 0, return -1.  */

int
floor_log2 (unsigned HOST_WIDE_INT x)
{
  int t = 0;

  if (x == 0)
    return -1;

#ifdef CLZ_HWI
  t = HOST_BITS_PER_WIDE_INT - 1 - (int) CLZ_HWI (x);
#else
  if (HOST_BITS_PER_WIDE_INT > 64)
    if (x >= (unsigned HOST_WIDE_INT) 1 << (t + 64))
      t += 64;
  if (HOST_BITS_PER_WIDE_INT > 32)
    if (x >= ((unsigned HOST_WIDE_INT) 1) << (t + 32))
      t += 32;
  if (x >= ((unsigned HOST_WIDE_INT) 1) << (t + 16))
    t += 16;
  if (x >= ((unsigned HOST_WIDE_INT) 1) << (t + 8))
    t += 8;
  if (x >= ((unsigned HOST_WIDE_INT) 1) << (t + 4))
    t += 4;
  if (x >= ((unsigned HOST_WIDE_INT) 1) << (t + 2))
    t += 2;
  if (x >= ((unsigned HOST_WIDE_INT) 1) << (t + 1))
    t += 1;
#endif

  return t;
}

/* Return the logarithm of X, base 2, considering X unsigned,
   if X is a power of 2.  Otherwise, returns -1.  */

int
exact_log2 (unsigned HOST_WIDE_INT x)
{
  if (x != (x & -x))
    return -1;
#ifdef CTZ_HWI
  return x ? CTZ_HWI (x) : -1;
#else
  return floor_log2 (x);
#endif
}
#endif /*  GCC_VERSION < 3004 || !defined (__cplusplus)  */