Current File : //usr/include/mysql/server/private/my_bit.h
/* Copyright (c) 2007, 2011, Oracle and/or its affiliates.
Copyright (c) 2009, 2017, MariaDB Corporation.
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 02110-1335 USA */
#ifndef MY_BIT_INCLUDED
#define MY_BIT_INCLUDED
/*
Some useful bit functions
*/
C_MODE_START
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;
}
/*
Count bits in 32bit integer
Algorithm by Sean Anderson, according to:
http://graphics.stanford.edu/~seander/bithacks.html
under "Counting bits set, in parallel"
(Original code public domain).
*/
static inline uint my_count_bits_uint32(uint32 v)
{
v = v - ((v >> 1) & 0x55555555);
v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
return (((v + (v >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
}
static inline uint my_count_bits(ulonglong x)
{
return my_count_bits_uint32((uint32)x) + my_count_bits_uint32((uint32)(x >> 32));
}
/*
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
(Original 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
((uint32)_my_bits_reverse_table[ key & 255] << 24) |
((uint32)_my_bits_reverse_table[(key>> 8) & 255] << 16) |
((uint32)_my_bits_reverse_table[(key>>16) & 255] << 8) |
(uint32)_my_bits_reverse_table[(key>>24) ];
}
/*
a number with the n lowest bits set
an overflow-safe version of (1 << n) - 1
*/
static inline uint64 my_set_bits(int n)
{
return (((1ULL << (n - 1)) - 1) << 1) | 1;
}
C_MODE_END
#endif /* MY_BIT_INCLUDED */
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