source: mainline/kernel/generic/src/adt/bitmap.c@ 64f3d3b

/*
 * Copyright (c) 2006 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup genericadt
 * @{
 */
/**
 * @file
 * @brief Implementation of bitmap ADT.
 *
 * This file implements bitmap ADT and provides functions for
 * setting and clearing ranges of bits and for finding ranges
 * of unset bits.
 *
 * The bitmap ADT can optionally implement a two-level hierarchy
 * for faster range searches. The second level bitmap (of blocks)
 * is not precise, but conservative. This means that if the block
 * bit is set, it guarantees that all bits in the block are set.
 * But if the block bit is unset, nothing can be said about the
 * bits in the block.
 *
 */

#include <adt/bitmap.h>
#include <typedefs.h>
#include <align.h>
#include <debug.h>
#include <macros.h>

#define ALL_ONES    0xff
#define ALL_ZEROES  0x00

/** Compute the size of a bitmap
 *
 * Compute the size of a bitmap that can store given number
 * of elements.
 *
 * @param elements Number of elements to store.
 *
 * @return Size of the bitmap (in units of BITMAP_ELEMENT bits).
 *
 */
static size_t bitmap_bytes(size_t elements)
{
        size_t bytes = elements / BITMAP_ELEMENT;
        
        if ((elements % BITMAP_ELEMENT) != 0)
                bytes++;
        
        return bytes;
}

/** Compute the number of 2nd level blocks
 *
 * Compute the number of 2nd level blocks for a given number
 * of elements.
 *
 * @param elements   Number of elements.
 * @param block_size Number of elements in one block.
 *
 * @return Number of 2nd level blocks.
 * @return Zero if block_size is zero.
 *
 */
static size_t bitmap_blocks(size_t elements, size_t block_size)
{
        if (block_size == 0)
                return 0;
        
        size_t blocks = elements / block_size;
        
        if ((elements % block_size) != 0)
                blocks++;
        
        return blocks;
}

/** Unchecked version of bitmap_get()
 *
 * This version of bitmap_get() does not do any boundary checks.
 *
 * @param bitmap  Bitmap to access.
 * @param element Element to access.
 *
 * @return Bit value of the element in the bitmap.
 *
 */
static unsigned int bitmap_get_fast(bitmap_t *bitmap, size_t element)
{
        return !!((bitmap->bits)[element / BITMAP_ELEMENT] &
            (1 << (element & BITMAP_REMAINER)));
}

/** Get bitmap size
 *
 * Return the size (in bytes) required for the bitmap.
 *
 * @param elements   Number bits stored in bitmap.
 * @param block_size Block size of the 2nd level bitmap.
 *                   If set to zero, no 2nd level is used.
 *
 * @return Size (in bytes) required for the bitmap.
 *
 */
size_t bitmap_size(size_t elements, size_t block_size)
{
        size_t blocks = bitmap_blocks(elements, block_size);
        
        return (bitmap_bytes(elements) + bitmap_bytes(blocks));
}

/** Initialize bitmap.
 *
 * No portion of the bitmap is set or cleared by this function.
 *
 * @param bitmap     Bitmap structure.
 * @param elements   Number of bits stored in bitmap.
 * @param block_size Block size of the 2nd level bitmap.
 *                   If set to zero, no 2nd level is used.
 * @param data       Address of the memory used to hold the map.
 *                   The optional 2nd level bitmap follows the 1st
 *                   level bitmap.
 *
 */
void bitmap_initialize(bitmap_t *bitmap, size_t elements, size_t block_size,
    void *data)
{
        bitmap->elements = elements;
        bitmap->bits = (uint8_t *) data;
        
        if (block_size > 0) {
                bitmap->block_size = block_size;
                bitmap->blocks = bitmap->bits +
                    bitmap_size(elements, 0);
        } else {
                bitmap->block_size = 0;
                bitmap->blocks = NULL;
        }
}

static void bitmap_set_range_internal(uint8_t *bits, size_t start, size_t count)
{
        if (count == 0)
                return;
        
        size_t aligned_start = ALIGN_UP(start, BITMAP_ELEMENT);
        
        /* Leading unaligned bits */
        size_t lub = min(aligned_start - start, count);
        
        /* Aligned middle bits */
        size_t amb = (count > lub) ? (count - lub) : 0;
        
        /* Trailing aligned bits */
        size_t tab = amb % BITMAP_ELEMENT;
        
        if (start + count < aligned_start) {
                /* Set bits in the middle of byte. */
                bits[start / BITMAP_ELEMENT] |=
                    ((1 << lub) - 1) << (start & BITMAP_REMAINER);
                return;
        }
        
        if (lub) {
                /* Make sure to set any leading unaligned bits. */
                bits[start / BITMAP_ELEMENT] |=
                    ~((1 << (BITMAP_ELEMENT - lub)) - 1);
        }
        
        size_t i;
        
        for (i = 0; i < amb / BITMAP_ELEMENT; i++) {
                /* The middle bits can be set byte by byte. */
                bits[aligned_start / BITMAP_ELEMENT + i] = ALL_ONES;
        }
        
        if (tab) {
                /* Make sure to set any trailing aligned bits. */
                bits[aligned_start / BITMAP_ELEMENT + i] |= (1 << tab) - 1;
        }
}

/** Set range of bits.
 *
 * @param bitmap Bitmap structure.
 * @param start  Starting bit.
 * @param count  Number of bits to set.
 *
 */
void bitmap_set_range(bitmap_t *bitmap, size_t start, size_t count)
{
        ASSERT(start + count <= bitmap->elements);
        
        bitmap_set_range_internal(bitmap->bits, start, count);
        
        if (bitmap->block_size > 0) {
                size_t aligned_start = ALIGN_UP(start, bitmap->block_size);
                
                /* Leading unaligned bits */
                size_t lub = min(aligned_start - start, count);
                
                /* Aligned middle bits */
                size_t amb = (count > lub) ? (count - lub) : 0;
                
                size_t aligned_size = amb / bitmap->block_size;
                
                bitmap_set_range_internal(bitmap->blocks, aligned_start,
                    aligned_size);
        }
}

static void bitmap_clear_range_internal(uint8_t *bits, size_t start,
    size_t count)
{
        if (count == 0)
                return;
        
        size_t aligned_start = ALIGN_UP(start, BITMAP_ELEMENT);
        
        /* Leading unaligned bits */
        size_t lub = min(aligned_start - start, count);
        
        /* Aligned middle bits */
        size_t amb = (count > lub) ? (count - lub) : 0;
        
        /* Trailing aligned bits */
        size_t tab = amb % BITMAP_ELEMENT;
        
        if (start + count < aligned_start) {
                /* Set bits in the middle of byte */
                bits[start / BITMAP_ELEMENT] &=
                    ~(((1 << lub) - 1) << (start & BITMAP_REMAINER));
                return;
        }
        
        if (lub) {
                /* Make sure to clear any leading unaligned bits. */
                bits[start / BITMAP_ELEMENT] &=
                    (1 << (BITMAP_ELEMENT - lub)) - 1;
        }
        
        size_t i;
        
        for (i = 0; i < amb / BITMAP_ELEMENT; i++) {
                /* The middle bits can be cleared byte by byte. */
                bits[aligned_start / BITMAP_ELEMENT + i] = ALL_ZEROES;
        }
        
        if (tab) {
                /* Make sure to clear any trailing aligned bits. */
                bits[aligned_start / BITMAP_ELEMENT + i] &= ~((1 << tab) - 1);
        }
}

/** Clear range of bits.
 *
 * @param bitmap Bitmap structure.
 * @param start  Starting bit.
 * @param count  Number of bits to clear.
 *
 */
void bitmap_clear_range(bitmap_t *bitmap, size_t start, size_t count)
{
        ASSERT(start + count <= bitmap->elements);
        
        bitmap_clear_range_internal(bitmap->bits, start, count);
        
        if (bitmap->block_size > 0) {
                size_t aligned_start = start / bitmap->block_size;
                
                size_t aligned_end = (start + count) / bitmap->block_size;
                
                if (((start + count) % bitmap->block_size) != 0)
                        aligned_end++;
                
                size_t aligned_size = aligned_end - aligned_start;
                
                bitmap_clear_range_internal(bitmap->blocks, aligned_start,
                    aligned_size);
        }
}

/** Copy portion of one bitmap into another bitmap.
 *
 * @param dst   Destination bitmap.
 * @param src   Source bitmap.
 * @param count Number of bits to copy.
 *
 */
void bitmap_copy(bitmap_t *dst, bitmap_t *src, size_t count)
{
        ASSERT(count <= dst->elements);
        ASSERT(count <= src->elements);
        
        size_t i;
        
        for (i = 0; i < count / BITMAP_ELEMENT; i++)
                dst->bits[i] = src->bits[i];
        
        if (count % BITMAP_ELEMENT) {
                bitmap_clear_range(dst, i * BITMAP_ELEMENT,
                    count % BITMAP_ELEMENT);
                dst->bits[i] |= src->bits[i] &
                    ((1 << (count % BITMAP_ELEMENT)) - 1);
        }
}

static int constraint_satisfy(size_t index, size_t base, size_t constraint)
{
        return (((base + index) & constraint) == 0);
}

/** Find a continuous zero bit range
 *
 * Find a continuous zero bit range in the bitmap. The address
 * computed as the sum of the index of the first zero bit and
 * the base argument needs to be compliant with the constraint
 * (those bits that are set in the constraint cannot be set in
 * the address).
 *
 * If the index argument is non-NULL, the continuous zero range
 * is set and the index of the first bit is stored to index.
 * Otherwise the bitmap stays untouched.
 *
 * @param bitmap     Bitmap structure.
 * @param count      Number of continuous zero bits to find.
 * @param base       Address of the first bit in the bitmap.
 * @param constraint Constraint for the address of the first zero bit.
 * @param index      Place to store the index of the first zero
 *                   bit. Can be NULL (in which case the bitmap
 *                   is not modified).
 *
 * @return Non-zero if a continuous range of zero bits satisfying
 *         the constraint has been found.
 * @return Zero otherwise.
 *
 */
int bitmap_allocate_range(bitmap_t *bitmap, size_t count, size_t base,
    size_t constraint, size_t *index)
{
        if (count == 0)
                return false;
        
        size_t bytes = bitmap_bytes(bitmap->elements);
        
        for (size_t byte = 0; byte < bytes; byte++) {
                /* Skip if the current byte has all bits set */
                if (bitmap->bits[byte] == ALL_ONES)
                        continue;
                
                size_t byte_bit = byte * BITMAP_ELEMENT;
                
                for (size_t bit = 0; bit < BITMAP_ELEMENT; bit++) {
                        size_t i = byte_bit + bit;
                        
                        if (i >= bitmap->elements)
                                break;
                        
                        if (!constraint_satisfy(i, base, constraint))
                                continue;
                        
                        if (!bitmap_get_fast(bitmap, i)) {
                                bool continuous = true;
                                
                                for (size_t j = 1; j < count; j++) {
                                        if ((i + j >= bitmap->elements) ||
                                            (bitmap_get_fast(bitmap, i + j))) {
                                                continuous = false;
                                                break;
                                        }
                                }
                                
                                if (continuous) {
                                        if (index != NULL) {
                                                bitmap_set_range(bitmap, i, count);
                                                *index = i;
                                        }
                                        
                                        return true;
                                }
                        }
                }
        }
        
        return false;
}

/** @}
 */