mem.cpp

/*
   The MIT License (MIT)

   Copyright (c) 2016 Tomasz Koziara

   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, sublicense, 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 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 NONINFRINGEMENT. IN NO EVENT SHALL THE
   AUTHORS OR COPYRIGHT HOLDERS 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.
 */

#include <string.h>
#include <stdlib.h>
#include "macros.h"
#include "mem.h"

typedef struct { void *p; size_t margin; } PTR; /* pointer with margin */

void* MEM_CALLOC (size_t size)
{
  void *chunk;

  if (!(chunk = malloc (size))) return NULL;

  memset (chunk, 0, size);

  return chunk;
}

void MEM_Init (MEM *pool, size_t chunksize, size_t chunksinblock)
{
  /* set chunksize not less than 'unsigned long' size
   * as wee plan to use chunks as items of 'deadchunks' list */
  pool->chunksize = (chunksize > sizeof(PTR) ? chunksize : sizeof(PTR));
  pool->chunksinblock = chunksinblock;
  pool->blocks = NULL;
  pool->freechunk = NULL;
  pool->lastchunk = NULL;
  pool->deadchunks = NULL;
}

void* MEM_Alloc (MEM *pool)
{
  void *chunk, *block;

  if (pool->deadchunks)
  { /* if there are deallocated chunks, get one */

    chunk = pool->deadchunks;
    pool->deadchunks = ((PTR*)pool->deadchunks)->p;
    memset (chunk, 0, pool->chunksize);
    return chunk;
  }
  else if (pool->freechunk == pool->lastchunk)
  { /* else if we need to allocate a new block ... */

    /* allocate a block of memory */
    block = malloc (pool->chunksize * pool->chunksinblock + sizeof(PTR));
    if (!block) return NULL; /* do not exit() here */
    memset (block, 0, pool->chunksize * pool->chunksinblock + sizeof(PTR));

    /* insert allocated block into the list */
    ((PTR*)block)->p = pool->blocks;
    pool->blocks = block;
    /* set free and last chunk */
    pool->freechunk = (char*)block + sizeof(PTR);
    pool->lastchunk = pool->freechunk + pool->chunksize * pool->chunksinblock;
  }

  chunk = pool->freechunk;
  pool->freechunk += pool->chunksize;
  return chunk;
}

void MEM_Free (MEM *pool, void *chunk)
{
  /* insert chunk into dead chunks list */
  ((PTR*)chunk)->p = pool->deadchunks;
  pool->deadchunks = chunk;
}

size_t MEM_Size (MEM *pool)
{
  size_t size = 0, chunk = pool->chunksize *
    pool->chunksinblock + sizeof(PTR);

  void *block = pool->blocks;

  /* loop over all blocks */  
  while (block)
  {
    block = ((PTR*)block)->p;
    size += chunk;
  }

  return size;
}

void MEM_Release (MEM *pool)
{
  void *block = pool->blocks;
  size_t next;

  /* traverse and free all blocks of memory */
  while (block)
  {
    next = *((size_t*)block);
    free (block);
    block = (void*)next;
  }

  pool->blocks = NULL;
  pool->freechunk = NULL;
  pool->lastchunk = NULL;
  pool->deadchunks = NULL;
}