xfs_bit.c

linux 内核源代码

/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * 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.
 *
 * This program is distributed in the hope that it would 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 the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_bit.h"
#include "xfs_log.h"
#include "xfs_trans.h"
#include "xfs_buf_item.h"

/*
 * XFS bit manipulation routines, used in non-realtime code.
 */

#ifndef HAVE_ARCH_HIGHBIT
/*
 * Index of high bit number in byte, -1 for none set, 0..7 otherwise.
 */
static const char xfs_highbit[256] = {
       -1, 0, 1, 1, 2, 2, 2, 2,			/* 00 .. 07 */
	3, 3, 3, 3, 3, 3, 3, 3,			/* 08 .. 0f */
	4, 4, 4, 4, 4, 4, 4, 4,			/* 10 .. 17 */
	4, 4, 4, 4, 4, 4, 4, 4,			/* 18 .. 1f */
	5, 5, 5, 5, 5, 5, 5, 5,			/* 20 .. 27 */
	5, 5, 5, 5, 5, 5, 5, 5,			/* 28 .. 2f */
	5, 5, 5, 5, 5, 5, 5, 5,			/* 30 .. 37 */
	5, 5, 5, 5, 5, 5, 5, 5,			/* 38 .. 3f */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 40 .. 47 */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 48 .. 4f */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 50 .. 57 */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 58 .. 5f */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 60 .. 67 */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 68 .. 6f */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 70 .. 77 */
	6, 6, 6, 6, 6, 6, 6, 6,			/* 78 .. 7f */
	7, 7, 7, 7, 7, 7, 7, 7,			/* 80 .. 87 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* 88 .. 8f */
	7, 7, 7, 7, 7, 7, 7, 7,			/* 90 .. 97 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* 98 .. 9f */
	7, 7, 7, 7, 7, 7, 7, 7,			/* a0 .. a7 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* a8 .. af */
	7, 7, 7, 7, 7, 7, 7, 7,			/* b0 .. b7 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* b8 .. bf */
	7, 7, 7, 7, 7, 7, 7, 7,			/* c0 .. c7 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* c8 .. cf */
	7, 7, 7, 7, 7, 7, 7, 7,			/* d0 .. d7 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* d8 .. df */
	7, 7, 7, 7, 7, 7, 7, 7,			/* e0 .. e7 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* e8 .. ef */
	7, 7, 7, 7, 7, 7, 7, 7,			/* f0 .. f7 */
	7, 7, 7, 7, 7, 7, 7, 7,			/* f8 .. ff */
};
#endif

/*
 * xfs_highbit32: get high bit set out of 32-bit argument, -1 if none set.
 */
inline int
xfs_highbit32(
	__uint32_t	v)
{
#ifdef HAVE_ARCH_HIGHBIT
	return highbit32(v);
#else
	int		i;

	if (v & 0xffff0000)
		if (v & 0xff000000)
			i = 24;
		else
			i = 16;
	else if (v & 0x0000ffff)
		if (v & 0x0000ff00)
			i = 8;
		else
			i = 0;
	else
		return -1;
	return i + xfs_highbit[(v >> i) & 0xff];
#endif
}

/*
 * xfs_lowbit64: get low bit set out of 64-bit argument, -1 if none set.
 */
int
xfs_lowbit64(
	__uint64_t	v)
{
	__uint32_t	w = (__uint32_t)v;
	int		n = 0;

	if (w) {	/* lower bits */
		n = ffs(w);
	} else {	/* upper bits */
		w = (__uint32_t)(v >> 32);
		if (w && (n = ffs(w)))
			n += 32;
	}
	return n - 1;
}

/*
 * xfs_highbit64: get high bit set out of 64-bit argument, -1 if none set.
 */
int
xfs_highbit64(
	__uint64_t	v)
{
	__uint32_t	h = (__uint32_t)(v >> 32);

	if (h)
		return xfs_highbit32(h) + 32;
	return xfs_highbit32((__uint32_t)v);
}


/*
 * Return whether bitmap is empty.
 * Size is number of words in the bitmap, which is padded to word boundary
 * Returns 1 for empty, 0 for non-empty.
 */
int
xfs_bitmap_empty(uint *map, uint size)
{
	uint i;
	uint ret = 0;

	for (i = 0; i < size; i++) {
		ret |= map[i];
	}

	return (ret == 0);
}

/*
 * Count the number of contiguous bits set in the bitmap starting with bit
 * start_bit.  Size is the size of the bitmap in words.
 */
int
xfs_contig_bits(uint *map, uint	size, uint start_bit)
{
	uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
	uint result = 0;
	uint tmp;

	size <<= BIT_TO_WORD_SHIFT;

	ASSERT(start_bit < size);
	size -= start_bit & ~(NBWORD - 1);
	start_bit &= (NBWORD - 1);
	if (start_bit) {
		tmp = *p++;
		/* set to one first offset bits prior to start */
		tmp |= (~0U >> (NBWORD-start_bit));
		if (tmp != ~0U)
			goto found;
		result += NBWORD;
		size -= NBWORD;
	}
	while (size) {
		if ((tmp = *p++) != ~0U)
			goto found;
		result += NBWORD;
		size -= NBWORD;
	}
	return result - start_bit;
found:
	return result + ffz(tmp) - start_bit;
}

/*
 * This takes the bit number to start looking from and
 * returns the next set bit from there.  It returns -1
 * if there are no more bits set or the start bit is
 * beyond the end of the bitmap.
 *
 * Size is the number of words, not bytes, in the bitmap.
 */
int xfs_next_bit(uint *map, uint size, uint start_bit)
{
	uint * p = ((unsigned int *) map) + (start_bit >> BIT_TO_WORD_SHIFT);
	uint result = start_bit & ~(NBWORD - 1);
	uint tmp;

	size <<= BIT_TO_WORD_SHIFT;

	if (start_bit >= size)
		return -1;
	size -= result;
	start_bit &= (NBWORD - 1);
	if (start_bit) {
		tmp = *p++;
		/* set to zero first offset bits prior to start */
		tmp &= (~0U << start_bit);
		if (tmp != 0U)
			goto found;
		result += NBWORD;
		size -= NBWORD;
	}
	while (size) {
		if ((tmp = *p++) != 0U)
			goto found;
		result += NBWORD;
		size -= NBWORD;
	}
	return -1;
found:
	return result + ffs(tmp) - 1;
}