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135 lines
3.4 KiB
C
135 lines
3.4 KiB
C
/* Copyright (c) 2007, 2011, Oracle and/or its affiliates.
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Copyright (c) 2009, 2017, MariaDB Corporation.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */
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#ifndef MY_BIT_INCLUDED
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#define MY_BIT_INCLUDED
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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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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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/*
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Count bits in 32bit integer
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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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under "Counting bits set, in parallel"
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(Original code public domain).
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*/
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static inline uint my_count_bits_uint32(uint32 v)
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{
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v = v - ((v >> 1) & 0x55555555);
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v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
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return (((v + (v >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
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}
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static inline uint my_count_bits(ulonglong x)
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{
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return my_count_bits_uint32((uint32)x) + my_count_bits_uint32((uint32)(x >> 32));
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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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(Original 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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((uint32)_my_bits_reverse_table[ key & 255] << 24) |
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((uint32)_my_bits_reverse_table[(key>> 8) & 255] << 16) |
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((uint32)_my_bits_reverse_table[(key>>16) & 255] << 8) |
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(uint32)_my_bits_reverse_table[(key>>24) ];
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}
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/*
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a number with the n lowest bits set
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an overflow-safe version of (1 << n) - 1
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*/
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static inline uint64 my_set_bits(int n)
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{
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return (((1ULL << (n - 1)) - 1) << 1) | 1;
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}
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/* Create a mask of the significant bits for the last byte (1,3,7,..255) */
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static inline uchar last_byte_mask(uint bits)
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{
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/* Get the number of used bits-1 (0..7) in the last byte */
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unsigned int const used = (bits - 1U) & 7U;
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/* Return bitmask for the significant bits */
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return ((2U << used) - 1);
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}
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C_MODE_END
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#endif /* MY_BIT_INCLUDED */
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