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Diffstat (limited to 'mysql/my_bit.h')
| -rw-r--r-- | mysql/my_bit.h | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/mysql/my_bit.h b/mysql/my_bit.h new file mode 100644 index 0000000..8d9f485 --- /dev/null +++ b/mysql/my_bit.h @@ -0,0 +1,124 @@ +/* + Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; version 2 of the License. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */ + +#ifndef MY_BIT_INCLUDED +#define MY_BIT_INCLUDED + +/* + Some useful bit functions +*/ + +C_MODE_START + +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_uint32(uint32 v) +{ + 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)]); +} + + +/* + 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) ]; +} + +C_MODE_END + +#endif /* MY_BIT_INCLUDED */ |