C++ (Cpp) COUNT_STEP Beispiele

Beispiel #1

Datei: bt.c Projekt: RobertDash/pspp

/* Returns the number of high-order 0-bits in X.
   Undefined if X is zero. */
static inline int
count_leading_zeros (size_t x)
{
#if __GNUC__ >= 4
#if SIZE_MAX > ULONG_MAX
  return __builtin_clzll (x);
#elif SIZE_MAX > UINT_MAX
  return __builtin_clzl (x);
#else
  return __builtin_clz (x);
#endif
#else
  /* This algorithm is from _Hacker's Delight_ section 5.3. */
  size_t y;
  int n;

#define COUNT_STEP(BITS)                        \
        y = x >> BITS;                          \
        if (y != 0)                             \
          {                                     \
            n -= BITS;                          \
            x = y;                              \
          }

  n = sizeof (size_t) * CHAR_BIT;
#if SIZE_MAX >> 31 >> 31 >> 2
  COUNT_STEP (64);
#endif
#if SIZE_MAX >> 31 >> 1
  COUNT_STEP (32);
#endif
  COUNT_STEP (16);
  COUNT_STEP (8);
  COUNT_STEP (4);
  COUNT_STEP (2);
  y = x >> 1;
  return y != 0 ? n - 2 : n - x;
#endif
}

Beispiel #2

Datei: scapegoat.c Projekt: asmloverX/childish-codes

/* Returns the number of high-order 0-bits in X.
   Undefined if X is zero. */
static size_t count_leading_zeros (size_t x)
{
  /* This algorithm is from _Hacker's Delight_ section 5.3. */
  size_t y;
  size_t n;

#define COUNT_STEP(BITS) y = x >> BITS; if (y != 0){n -= BITS; x = y; }

  n = sizeof (size_t) * CHAR_BIT;
#if SIZE_MAX >> 31 >> 31 >> 2
  COUNT_STEP (64);
#endif
#if SIZE_MAX >> 31 >> 1
  COUNT_STEP (32);
#endif
  COUNT_STEP (16);
  COUNT_STEP (8);
  COUNT_STEP (4);
  COUNT_STEP (2);
  y = x >> 1;
  return y != 0 ? n - 2 : n - x;
}