libgit2/src/revobject.c

/*
 * This file is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, version 2,
 * as published by the Free Software Foundation.
 *
 * In addition to the permissions in the GNU General Public License,
 * the authors give you unlimited permission to link the compiled
 * version of this file into combinations with other programs,
 * and to distribute those combinations without any restriction
 * coming from the use of this file.  (The General Public License
 * restrictions do apply in other respects; for example, they cover
 * modification of the file, and distribution when not linked into
 * a combined executable.)
 *
 * This file 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; see the file COPYING.  If not, write to
 * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

#include "common.h"
#include "revobject.h"

const float max_load_factor = 0.65;

unsigned int git_revpool_table__hash(const git_oid *id)
{
	const unsigned int m = 0x5bd1e995;
	const int r = 24;

	unsigned int h = 0xA8A3D5;
    int i;

    for (i = 0; i < GIT_OID_RAWSZ / 4; ++i)
    {
		unsigned int k = ((unsigned int *)id->id)[i];

		k *= m;
		k ^= k >> r;
		k *= m;
		h *= m;
		h ^= k;
    }

	h ^= h >> 13;
	h *= m;
	h ^= h >> 15;

	return h;
}

git_revpool_table *git_revpool_table_create(unsigned int min_size)
{
    git_revpool_table *table;

    table = git__malloc(sizeof(table));

    if (table == NULL)
        return NULL;

    // round up size to closest power of 2
    min_size--;
    min_size |= min_size >> 1;
    min_size |= min_size >> 2;
    min_size |= min_size >> 4;
    min_size |= min_size >> 8;
    min_size |= min_size >> 16;

    table->size_mask = min_size;
    table->count = 0;
    table->max_count = (min_size + 1) * max_load_factor;

    table->nodes = git__malloc((min_size + 1) * sizeof(git_revpool_node *));

    if (table->nodes == NULL)
    {
        free(table);
        return NULL;
    }

    memset(table->nodes, 0x0, (min_size + 1) * sizeof(git_revpool_node *));

    return table;
}

int git_revpool_table_insert(git_revpool_table *table, git_revpool_object *object)
{
    git_revpool_node *node;
    unsigned int index, hash;

    if (table->count + 1 > table->max_count)
        git_revpool_table_resize(table);

    node = git__malloc(sizeof(git_revpool_node));
    if (node == NULL)
        return -1;

    hash = git_revpool_table__hash(&object->id);
    index = (hash & table->size_mask);

    node->object = object;
    node->hash = hash;
    node->next = table->nodes[index];

    table->nodes[index] = node;
    table->count++;

    return 0;
}

git_revpool_object *git_revpool_table_lookup(git_revpool_table *table, const git_oid *id)
{
    git_revpool_node *node;
    unsigned int index, hash;

    hash = git_revpool_table__hash(id);
    index = (hash & table->size_mask);
    node = table->nodes[index];

    while (node != NULL)
    {
        if (node->hash == hash && git_oid_cmp(id, &node->object->id) == 0)
            return node->object;

        node = node->next;
    }

    return NULL;
}

void git_revpool_table_resize(git_revpool_table *table)
{
    git_revpool_node **new_nodes;
    unsigned int new_size, i;

    new_size = (table->size_mask + 1) * 2;

    new_nodes = git__malloc(new_size * sizeof(git_revpool_node *));
    if (new_nodes == NULL)
        return;

    memset(new_nodes, 0x0, new_size * sizeof(git_revpool_node *));

    for (i = 0; i <= table->size_mask; ++i)
    {
        git_revpool_node *n;
        unsigned int index;

        while ((n = table->nodes[i]) != NULL)
        {
            table->nodes[i] = n->next;
            index = n->hash & (new_size - 1);
            n->next = new_nodes[index];
            new_nodes[index] = n;
        }
    }

    free(table->nodes);
    table->nodes = new_nodes;
    table->size_mask = (new_size - 1);
    table->max_count = new_size * max_load_factor;
}


void git_revpool_table_free(git_revpool_table *table)
{

}