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by brian
clean slate |
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/*
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Some useful bit functions
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*/
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C_MODE_START
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#ifdef HAVE_INLINE
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extern const char _my_bits_nbits[256]; |
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extern const uchar _my_bits_reverse_table[256]; |
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/*
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Find smallest X in 2^X >= value
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This can be used to divide a number with value by doing a shift instead
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*/
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STATIC_INLINE uint my_bit_log2(ulong value) |
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{
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uint bit; |
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for (bit=0 ; value > 1 ; value>>=1, bit++) ; |
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return bit; |
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}
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STATIC_INLINE uint my_count_bits(ulonglong v) |
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{
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#if SIZEOF_LONG_LONG > 4
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/* The following code is a bit faster on 16 bit machines than if we would
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only shift v */
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ulong v2=(ulong) (v >> 32); |
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return (uint) (uchar) (_my_bits_nbits[(uchar) v] + |
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_my_bits_nbits[(uchar) (v >> 8)] + |
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_my_bits_nbits[(uchar) (v >> 16)] + |
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_my_bits_nbits[(uchar) (v >> 24)] + |
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_my_bits_nbits[(uchar) (v2)] + |
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_my_bits_nbits[(uchar) (v2 >> 8)] + |
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_my_bits_nbits[(uchar) (v2 >> 16)] + |
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_my_bits_nbits[(uchar) (v2 >> 24)]); |
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#else
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return (uint) (uchar) (_my_bits_nbits[(uchar) v] + |
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_my_bits_nbits[(uchar) (v >> 8)] + |
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_my_bits_nbits[(uchar) (v >> 16)] + |
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_my_bits_nbits[(uchar) (v >> 24)]); |
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#endif
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}
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STATIC_INLINE uint my_count_bits_ushort(ushort v) |
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{
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return _my_bits_nbits[v]; |
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}
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/*
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Next highest power of two
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SYNOPSIS
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my_round_up_to_next_power()
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v Value to check
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RETURN
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Next or equal power of 2
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Note: 0 will return 0
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NOTES
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Algorithm by Sean Anderson, according to:
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http://graphics.stanford.edu/~seander/bithacks.html
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(Orignal code public domain)
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Comments shows how this works with 01100000000000000000000000001011
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*/
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STATIC_INLINE uint32 my_round_up_to_next_power(uint32 v) |
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{
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v--; /* 01100000000000000000000000001010 */ |
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v|= v >> 1; /* 01110000000000000000000000001111 */ |
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v|= v >> 2; /* 01111100000000000000000000001111 */ |
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v|= v >> 4; /* 01111111110000000000000000001111 */ |
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v|= v >> 8; /* 01111111111111111100000000001111 */ |
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v|= v >> 16; /* 01111111111111111111111111111111 */ |
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return v+1; /* 10000000000000000000000000000000 */ |
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}
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STATIC_INLINE uint32 my_clear_highest_bit(uint32 v) |
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{
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uint32 w=v >> 1; |
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w|= w >> 1; |
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w|= w >> 2; |
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w|= w >> 4; |
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w|= w >> 8; |
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w|= w >> 16; |
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return v & w; |
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}
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STATIC_INLINE uint32 my_reverse_bits(uint32 key) |
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{
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return
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(_my_bits_reverse_table[ key & 255] << 24) | |
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(_my_bits_reverse_table[(key>> 8) & 255] << 16) | |
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(_my_bits_reverse_table[(key>>16) & 255] << 8) | |
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_my_bits_reverse_table[(key>>24) ]; |
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}
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#else /* HAVE_INLINE */ |
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extern uint my_bit_log2(ulong value); |
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extern uint32 my_round_up_to_next_power(uint32 v); |
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uint32 my_clear_highest_bit(uint32 v); |
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uint32 my_reverse_bits(uint32 key); |
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extern uint my_count_bits(ulonglong v); |
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extern uint my_count_bits_ushort(ushort v); |
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#endif /* HAVE_INLINE */ |
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C_MODE_END
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