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/*
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 (uint32_t) (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
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