~drizzle-trunk/drizzle/development

/*

  Some useful bit functions

*/

#ifdef __cplusplus

extern "C" {

#endif

extern const char _my_bits_nbits[256];

extern const unsigned char _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 uint32_t my_bit_log2(uint32_t value)

{

  uint32_t bit;

  for (bit=0 ; value > 1 ; value>>=1, bit++) ;

  return bit;

}

static inline uint32_t my_count_bits(uint64_t v)

{

  /* The following code is a bit faster on 16 bit machines than if we would

     only shift v */

  uint32_t v2=(uint32_t) (v >> 32);

  return (uint) (unsigned char) (_my_bits_nbits[(unsigned char)  v] +

                         _my_bits_nbits[(unsigned char) (v >> 8)] +

                         _my_bits_nbits[(unsigned char) (v >> 16)] +

                         _my_bits_nbits[(unsigned char) (v >> 24)] +

                         _my_bits_nbits[(unsigned char) (v2)] +

                         _my_bits_nbits[(unsigned char) (v2 >> 8)] +

                         _my_bits_nbits[(unsigned char) (v2 >> 16)] +

                         _my_bits_nbits[(unsigned char) (v2 >> 24)]);

}

static inline uint32_t my_count_bits_uint16(uint16_t 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_t my_round_up_to_next_power(uint32_t 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_t my_clear_highest_bit(uint32_t v)

{

  uint32_t w=v >> 1;

  w|= w >> 1;

  w|= w >> 2;

  w|= w >> 4;

  w|= w >> 8;

  w|= w >> 16;

  return v & w;

}

static inline uint32_t my_reverse_bits(uint32_t 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)      ];

}

#ifdef __cplusplus

}

#endif