my_bit.h

#ifndef MY_BIT_INCLUDED
#define MY_BIT_INCLUDED

/*
  Some useful bit functions
*/

C_MODE_START
#ifdef HAVE_INLINE

extern const char _my_bits_nbits[256];
extern const uchar _my_bits_reverse_table[256];

/*
  Find smallest X in 2^X >= value
  This can be used to divide a number with value by doing a shift instead
*/

STATIC_INLINE uint my_bit_log2(ulong value)
{
  uint bit;
  for (bit=0 ; value > 1 ; value>>=1, bit++) ;
  return bit;
}

STATIC_INLINE uint my_count_bits(ulonglong v)
{
#if SIZEOF_LONG_LONG > 4
  /* The following code is a bit faster on 16 bit machines than if we would
     only shift v */
  ulong v2=(ulong) (v >> 32);
  return (uint) (uchar) (_my_bits_nbits[(uchar)  v] +
                         _my_bits_nbits[(uchar) (v >> 8)] +
                         _my_bits_nbits[(uchar) (v >> 16)] +
                         _my_bits_nbits[(uchar) (v >> 24)] +
                         _my_bits_nbits[(uchar) (v2)] +
                         _my_bits_nbits[(uchar) (v2 >> 8)] +
                         _my_bits_nbits[(uchar) (v2 >> 16)] +
                         _my_bits_nbits[(uchar) (v2 >> 24)]);
#else
  return (uint) (uchar) (_my_bits_nbits[(uchar)  v] +
                         _my_bits_nbits[(uchar) (v >> 8)] +
                         _my_bits_nbits[(uchar) (v >> 16)] +
                         _my_bits_nbits[(uchar) (v >> 24)]);
#endif
}

STATIC_INLINE uint my_count_bits_ushort(ushort v)
{
  return _my_bits_nbits[v];
}


/*
  Next highest power of two

  SYNOPSIS
    my_round_up_to_next_power()
    v		Value to check

  RETURN
    Next or equal power of 2
    Note: 0 will return 0

  NOTES
    Algorithm by Sean Anderson, according to:
    http://graphics.stanford.edu/~seander/bithacks.html
    (Orignal code public domain)

    Comments shows how this works with 01100000000000000000000000001011
*/

STATIC_INLINE uint32 my_round_up_to_next_power(uint32 v)
{
  v--;			/* 01100000000000000000000000001010 */
  v|= v >> 1;		/* 01110000000000000000000000001111 */
  v|= v >> 2;		/* 01111100000000000000000000001111 */
  v|= v >> 4;		/* 01111111110000000000000000001111 */
  v|= v >> 8;		/* 01111111111111111100000000001111 */
  v|= v >> 16;		/* 01111111111111111111111111111111 */
  return v+1;		/* 10000000000000000000000000000000 */
}

STATIC_INLINE uint32 my_clear_highest_bit(uint32 v)
{
  uint32 w=v >> 1;
  w|= w >> 1;
  w|= w >> 2;
  w|= w >> 4;
  w|= w >> 8;
  w|= w >> 16;
  return v & w;
}

STATIC_INLINE uint32 my_reverse_bits(uint32 key)
{
  return
    (_my_bits_reverse_table[ key      & 255] << 24) |
    (_my_bits_reverse_table[(key>> 8) & 255] << 16) |
    (_my_bits_reverse_table[(key>>16) & 255] <<  8) |
     _my_bits_reverse_table[(key>>24)      ];
}

#else  /* HAVE_INLINE */
extern uint my_bit_log2(ulong value);
extern uint32 my_round_up_to_next_power(uint32 v);
uint32 my_clear_highest_bit(uint32 v);
uint32 my_reverse_bits(uint32 key);
extern uint my_count_bits(ulonglong v);
extern uint my_count_bits_ushort(ushort v);
#endif /* HAVE_INLINE */
C_MODE_END

#endif /* MY_BIT_INCLUDED */