src/util/u_idalloc.c

/**************************************************************************
 *
 * Copyright 2017 Valve Corporation
 * All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sub license, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial portions
 * of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR
 * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 **************************************************************************/

/**
 * @file
 * A simple allocator that allocates and release "numbers".
 *
 * @author Samuel Pitoiset <samuel.pitoiset@gmail.com>
 */

#include "util/u_idalloc.h"
#include "util/u_math.h"
#include <stdlib.h>

void
util_idalloc_init(struct util_idalloc *buf)
{
   memset(buf, 0, sizeof(*buf));
}

void
util_idalloc_fini(struct util_idalloc *buf)
{
   if (buf->data)
      free(buf->data);
}

void
util_idalloc_resize(struct util_idalloc *buf, unsigned new_num_elements)
{
   new_num_elements = align(new_num_elements, 32);

   if (new_num_elements > buf->num_elements) {
      unsigned i;

      buf->data = realloc(buf->data,
                          (new_num_elements / 32) * sizeof(*buf->data));

      for (i = buf->num_elements / 32; i < new_num_elements / 32; i++)
         buf->data[i] = 0;
      buf->num_elements = new_num_elements;
   }
}

unsigned
util_idalloc_alloc(struct util_idalloc *buf)
{
   unsigned num_elements = buf->num_elements;

   for (unsigned i = buf->lowest_free_idx; i < num_elements / 32; i++) {
      if (buf->data[i] == 0xffffffff)
         continue;

      unsigned bit = ffs(~buf->data[i]) - 1;
      buf->data[i] |= 1u << bit;
      buf->lowest_free_idx = i;
      return i * 32 + bit;
   }

   /* No slots available, resize and return the first free. */
   util_idalloc_resize(buf, num_elements * 2);

   buf->lowest_free_idx = num_elements / 32;

   buf->data[num_elements / 32] |= 1 << (num_elements % 32);

   return num_elements;
}

void
util_idalloc_free(struct util_idalloc *buf, unsigned id)
{
   assert(id < buf->num_elements);
   unsigned idx = id / 32;
   buf->lowest_free_idx = MIN2(idx, buf->lowest_free_idx);
   buf->data[idx] &= ~(1 << (id % 32));
}

void
util_idalloc_reserve(struct util_idalloc *buf, unsigned id)
{
   assert(id < buf->num_elements);
   assert((buf->data[id / 32] & (1u << (id % 32))) == 0);
   buf->data[id / 32] |= 1u << (id % 32);
}