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/* bit-array.h - Bit array manipulation functions.
Copyright (C) 2007, 2008 Free Software Foundation, Inc.
Written by Neal H. Walfield <neal@gnu.org>.
This file is part of the GNU Hurd.
The GNU Hurd 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; either version 3 of the
License, or (at your option) any later version.
The GNU Hurd 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, see
<http://www.gnu.org/licenses/>. */
#ifndef _BIT_ARRAY_H_
#define _BIT_ARRAY_H_
#include <stdbool.h>
#include <assert.h>
/* Set bit BIT in array ARRAY (which is SIZE bytes long). Returns
true if bit was set, false otherwise. */
static inline bool
bit_set (unsigned char *array, int size, int bit)
{
assert (bit >= 0);
assert (bit < size * 8);
if ((array[bit / 8] & (1 << (bit & 0x7))))
/* Already set! */
return false;
array[bit / 8] |= 1 << (bit & 0x7);
return true;
}
/* Set bit BIT in array ARRAY (which is SIZE bytes long) to VALUE. */
static inline void
bit_set_to (unsigned char *array, int size, int bit, int value)
{
assert (bit >= 0);
assert (bit < size * 8);
if (value)
array[bit / 8] |= 1 << (bit & 0x7);
else
array[bit / 8] &= ~(1 << (bit & 0x7));
}
/* Allocate the first free (zero) bit starting at bit START_BIT. SIZE
is the size of ARRAY (in bytes). Returns -1 on failure, otherwise
the bit allocated. */
static inline int
bit_alloc (unsigned char *array, int size, int start_bit)
{
int first_free_bit[]
= { /* 0000 */ 0, /* 0001 */ 1, /* 0010 */ 0, /* 0011 */ 2,
/* 0100 */ 0, /* 0101 */ 1, /* 0110 */ 0, /* 0111 */ 3,
/* 1000 */ 0, /* 1001 */ 1, /* 1010 */ 0, /* 1011 */ 2,
/* 1100 */ 0, /* 1101 */ 1, /* 1110 */ 0, /* 1111 */ -1 };
int check_byte (unsigned char byte)
{
/* Check the lower four bits. */
int b = first_free_bit[byte & 0xf];
if (b != -1)
return b;
/* Check the uppoer four bits. */
b = first_free_bit[byte >> 4];
if (b != -1)
return 4 + b;
return -1;
}
assert (0 <= start_bit);
assert (start_bit < size * 8);
int start_byte = start_bit / 8;
int byte = start_byte;
unsigned char b;
if ((start_bit & 0x7) != 0)
/* We don't start on a byte boundary. */
{
b = array[byte] | ((1 << (start_bit & 0x7)) - 1);
goto check;
}
do
{
int bit;
b = array[byte];
check:
bit = check_byte (b);
if (bit != -1)
/* Got one! */
{
array[byte] |= 1 << bit;
return byte * 8 + bit;
}
byte ++;
if (byte == size)
byte = 0;
}
while (byte != start_byte);
if ((start_bit & 0x7) != 0)
{
b = array[byte] | ~((1 << (start_bit & 0x7)) - 1);
int bit = check_byte (b);
if (bit != -1)
/* Got one! */
{
array[byte] |= 1 << bit;
return byte * 8 + bit;
}
}
return -1;
}
static inline void
bit_dealloc (unsigned char *array, int bit)
{
assert ((array[bit / 8] & (1 << (bit & 0x7))));
/* Clear bit. */
array[bit / 8] &= ~(1 << (bit & 0x7));
}
static inline bool
bit_test (unsigned char *array, int bit)
{
return !! (array[bit / 8] & (1 << (bit & 0x7)));
}
#endif
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