malloc-lab/mm.c

/*
 * mm-naive.c - The fastest, least memory-efficient malloc package.
 *
 * In this naive approach, a block is allocated by simply incrementing
 * the brk pointer.  A block is pure payload. There are no headers or
 * footers.  Blocks are never coalesced or reused. Realloc is
 * implemented directly using mm_malloc and mm_free.
 *
 * NOTE TO STUDENTS: Replace this header comment with your own header
 * comment that gives a high level description of your solution.
 */
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <unistd.h>
#include <string.h>

#include "mm.h"
#include "memlib.h"

/*********************************************************
 * NOTE TO STUDENTS: Before you do anything else, please
 * provide your team information in the following struct.
 ********************************************************/
team_t team = {
  /* Team name */
  "anna.schlittenhardt@stud.uni-due.de+tuan-dat.tran@stud.uni-due.de",
  /* First member's full name */
  "Anna Schlittenhardt",
  /* First member's email address */
  "anna.schlittenhardt@stud.uni-due.de",
  /* Second member's full name (leave blank if none) */
  "Tuan-Dat Tran",
  /* Second member's email address (leave blank if none) */
  "tuan-dat.tran@stud.uni-due.de"
};

////////////////////////////////////////////////////////////////////////////////
/////////////////////////////////// STRUCTURE //////////////////////////////////
////////////////////////////////////////////////////////////////////////////////

// Filled Blk
//              31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// HEADER      | SIZE                                                                                       | A|
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// BP->        | ALLOCED MEMORY                                                                                |
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// FOOTER      | SIZE                                                                                       | A|
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// 
// Empty Blk
//              31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// HEADER      | SIZE                                                                                       | A|
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// BP->        | PTR TO PREV FREE BLK                                                                          |
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//             | PTR TO NEXT FREE BLK                                                                          |
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
//             | UNALLOC MEMORY                                                                                |
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
// FOOTER      | SIZE                                                                                       | A|
//             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

////////////////////////////////////////////////////////////////////////////////
//////////////////////////////////// DEFINES ///////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
/* single word (4) or double word (8) alignment */
#define ALIGNMENT 8

/* rounds up to the nearest multiple of ALIGNMENT */
#define ALIGN(size) (((size) + (ALIGNMENT-1)) & ~0x7)

#define SIZE_T_SIZE (ALIGN(sizeof(size_t)))

/* Page 830, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/* Basic constants and macros */
#define WSIZE 4 /* Word and header/footer size (bytes) */
#define DSIZE 8 /* Double word size (bytes) */
#define CHUNKSIZE (1<<12) /* Extend heap by this amount (bytes) */

#define MAX(x, y) ((x) > (y)? (x) : (y))
#define MIN(x, y) ((x) < (y)? (x) : (y))

/* Pack a size and allocated bit into a word */
#define PACK(size, alloc) ((size) | (alloc))

/* Read and write a word at address p */
#define GET(p) (*(unsigned int *)(p))
#define PUT(p, val) (*(unsigned int *)(p) = (val))

/* Read the size and allocated fields from address p */
#define GET_SIZE(p) (GET(p) & ~0x7)
#define GET_ALLOC(p) (GET(p) & 0x1)

/* Given block ptr bp, compute address of its header and footer */
#define HDRP(bp) ((char *)(bp) - WSIZE)
#define FTRP(bp) ((char *)(bp) + GET_SIZE(HDRP(bp)) - DSIZE)

/* Given block ptr bp, compute address of next and previous blocks */
#define NEXT_BLKP(bp) ((char *)(bp) + GET_SIZE(((char *)(bp) - WSIZE)))
#define PREV_BLKP(bp) ((char *)(bp) - GET_SIZE(((char *)(bp) - DSIZE)))

#define PUT_PTR(p, ptr) (*(unsigned int *)(p) = (unsigned int)(ptr))

#define PRV_PTR(ptr) ((char *)(ptr))
#define NXT_PTR(ptr) ((char *)(ptr) + WSIZE)

#define PRV_BLK(ptr) (*(char **)(ptr))
#define NXT_BLK(ptr) (*(char **)(NXT_PTR(ptr)))

////////////////////////////////////////////////////////////////////////////////
////////////////////////////////// GLOBAL VARS /////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
#define LISTSIZE 20
static char* heap_listp;
char* seg_list[LISTSIZE];

////////////////////////////////////////////////////////////////////////////////
///////////////////////////////// HELPER PREDEF //////////////////////////////// 
////////////////////////////////////////////////////////////////////////////////
static void *extend_heap(size_t size);
static void add_free(void *ptr, size_t size);
static void remove_free(void *ptr);
static void *coalesce(void *ptr);
static void *place(void *ptr, size_t asize);
static int getSzClass(size_t asize);

////////////////////////////////////////////////////////////////////////////////
/////////////////////////////// HELPER FUNCTIONS /////////////////////////////// 
////////////////////////////////////////////////////////////////////////////////
static int getSzClass(size_t asize) {
  for (size_t i = 0; i < LISTSIZE; ++i) {
    if (asize == (1 << i)) {
      return i;
    }
  }
  return LISTSIZE-1;
}

static void *extend_heap(size_t size)
{
  size_t asize;
  asize = ALIGN(size);
  void *ptr;                   
    
  if ((ptr = mem_sbrk(asize)) == (void *)-1)
    return NULL;
    
  /* Set Header and Footer*/
  PUT(HDRP(ptr), PACK(asize, 0));  
  PUT(FTRP(ptr), PACK(asize, 0));   
  PUT(HDRP(NEXT_BLKP(ptr)), PACK(0, 1)); 

  add_free(ptr, asize);

  return coalesce(ptr);
}

static void add_free(void *ptr, size_t size) {
  int szClass = getSzClass(size);
  void* class_ptr = seg_list[szClass];
  void *pre_ptr = NULL;

  while ((class_ptr != NULL) && (size > GET_SIZE(HDRP(class_ptr)))) {
    pre_ptr = class_ptr;
    class_ptr = PRV_BLK(class_ptr);
  }
    
  if (class_ptr != NULL && pre_ptr != NULL) {
    PUT_PTR(NXT_PTR(class_ptr), ptr);
    PUT_PTR(NXT_PTR(ptr), pre_ptr);
    PUT_PTR(PRV_PTR(ptr), class_ptr);
    PUT_PTR(PRV_PTR(pre_ptr), ptr);
  } 
  else if (class_ptr != NULL && pre_ptr == NULL) {
    PUT_PTR(PRV_PTR(ptr), class_ptr);
    PUT_PTR(NXT_PTR(class_ptr), ptr);
    PUT_PTR(NXT_PTR(ptr), NULL);
    seg_list[szClass] = ptr;
  } 
  else if(class_ptr == NULL && pre_ptr != NULL) {
    PUT_PTR(NXT_PTR(ptr), pre_ptr);
    PUT_PTR(PRV_PTR(ptr), NULL);
    PUT_PTR(PRV_PTR(pre_ptr), ptr);
  } 
  else {
    PUT_PTR(NXT_PTR(ptr), NULL);
    PUT_PTR(PRV_PTR(ptr), NULL);
    seg_list[szClass] = ptr;
  }
    
  return;
}


static void remove_free(void *ptr) {
  size_t size = GET_SIZE(HDRP(ptr));
  int szClass = getSzClass(size);
    
  if (PRV_BLK(ptr) != NULL && NXT_BLK(ptr) != NULL) {
    PUT_PTR(NXT_PTR(PRV_BLK(ptr)), NXT_BLK(ptr));
    PUT_PTR(PRV_PTR(NXT_BLK(ptr)), PRV_BLK(ptr));
  } else if(PRV_BLK(ptr) != NULL && NXT_BLK(ptr) == NULL) {
    PUT_PTR(NXT_PTR(PRV_BLK(ptr)), NULL);
    seg_list[szClass] = PRV_BLK(ptr);
  } 
  else if(PRV_BLK(ptr) == NULL && NXT_BLK(ptr) != NULL) {
    PUT_PTR(PRV_PTR(NXT_BLK(ptr)), NULL);
  } else {
    seg_list[szClass] = NULL;
  }  
  return;
}


static void *coalesce(void *ptr) {
  size_t prev_alloc = GET_ALLOC(HDRP(PREV_BLKP(ptr)));
  size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(ptr)));
  size_t size = GET_SIZE(HDRP(ptr));
    
  if (prev_alloc && next_alloc) {                         // Case 1
    return ptr;
  }
  else if (prev_alloc && !next_alloc) {                   // Case 2
    remove_free(ptr);
    remove_free(NEXT_BLKP(ptr));
    size += GET_SIZE(HDRP(NEXT_BLKP(ptr)));
    PUT(HDRP(ptr), PACK(size, 0));
    PUT(FTRP(ptr), PACK(size, 0));
  } else if (!prev_alloc && next_alloc) {                 // Case 3 
    remove_free(ptr);
    remove_free(PREV_BLKP(ptr));
    size += GET_SIZE(HDRP(PREV_BLKP(ptr)));
    PUT(FTRP(ptr), PACK(size, 0));
    PUT(HDRP(PREV_BLKP(ptr)), PACK(size, 0));
    ptr = PREV_BLKP(ptr);
  } else {                                                // Case 4
    remove_free(ptr);
    remove_free(PREV_BLKP(ptr));
    remove_free(NEXT_BLKP(ptr));
    size += GET_SIZE(HDRP(PREV_BLKP(ptr))) + GET_SIZE(HDRP(NEXT_BLKP(ptr)));
    PUT(HDRP(PREV_BLKP(ptr)), PACK(size, 0));
    PUT(FTRP(NEXT_BLKP(ptr)), PACK(size, 0));
    ptr = PREV_BLKP(ptr);
  }
    
  add_free(ptr, size);
    
  return ptr;
}

static void *place(void *ptr, size_t asize) {
  size_t ptr_size = GET_SIZE(HDRP(ptr));
  size_t remainder = ptr_size - asize;
    
  remove_free(ptr);
    
  if (remainder <= DSIZE * 2) {
    PUT(HDRP(ptr), PACK(ptr_size, 1)); 
    PUT(FTRP(ptr), PACK(ptr_size, 1)); 
  }
  else if (asize >= 100) {
    PUT(HDRP(ptr), PACK(remainder, 0));
    PUT(FTRP(ptr), PACK(remainder, 0));
    PUT(HDRP(NEXT_BLKP(ptr)), PACK(asize, 1));
    PUT(FTRP(NEXT_BLKP(ptr)), PACK(asize, 1));
    add_free(ptr, remainder);
    return NEXT_BLKP(ptr);
  } else {
    PUT(HDRP(ptr), PACK(asize, 1)); 
    PUT(FTRP(ptr), PACK(asize, 1)); 
    PUT(HDRP(NEXT_BLKP(ptr)), PACK(remainder, 0)); 
    PUT(FTRP(NEXT_BLKP(ptr)), PACK(remainder, 0)); 
    add_free(NEXT_BLKP(ptr), remainder);
  }
  return ptr;
}

////////////////////////////////////////////////////////////////////////////////
////////////////////////////// MAIN FUNCTIONALITY //////////////////////////////
////////////////////////////////////////////////////////////////////////////////
/* Page 831, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/*
 * mm_init - initialize the malloc package.
 */
int mm_init(void)
{
  // Init seg_list
  for (size_t i = 0; i < LISTSIZE; ++i) {
    seg_list[i] = NULL;
  }

  /* Create the initial empty heap */
  if ((heap_listp = mem_sbrk(4*WSIZE)) == (void *)-1)
    return -1;
  PUT(heap_listp, 0); /* Alignment padding */
  PUT(heap_listp + (1*WSIZE), PACK(DSIZE, 1)); /* Prologue header */
  PUT(heap_listp + (2*WSIZE), PACK(DSIZE, 1)); /* Prologue footer */
  PUT(heap_listp + (3*WSIZE), PACK(0, 1));   /* Epilogue header */
  heap_listp += (2*WSIZE);

  /* Extend the empty heap with a free block of CHUNKSIZE bytes */
  if (extend_heap(CHUNKSIZE/WSIZE) == NULL)
    return -1;
  return 0;
}

/* Page 834, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/*
 * mm_malloc - Allocate a block by incrementing the brk pointer.
 *     Always allocate a block whose size is a multiple of the alignment.
 */
void *mm_malloc(size_t size)
{
  size_t asize;      /* Adjusted block size */
  size_t extendsize; /* Amount to extend heap if no fit */
  void *ptr;  /* Pointer */
    
  if (size == 0)
    return NULL;
    
  if (size <= DSIZE) {
    asize = 2 * DSIZE;
  } else {
    asize = ALIGN(size+DSIZE);
  }
    
  size_t sz = asize;
  for (int i = 0;i < LISTSIZE; ++i) {
    if ((i == LISTSIZE-1) || ((sz < 2) && (seg_list[i] != NULL))) {
      ptr = seg_list[i];
      while ((ptr != NULL) && (asize > GET_SIZE(HDRP(ptr))))
        {
          ptr = PRV_BLK(ptr);
        }
      if (ptr != NULL)
        break;
    }
    sz >>= 1;
  }
    
  if (ptr == NULL) {
    extendsize = MAX(asize, CHUNKSIZE);
        
    if ((ptr = extend_heap(extendsize)) == NULL)
      return NULL;
  }
    
  return place(ptr, asize);
}

/* Page 833, Pearson R. Bryant – D. O’Hallaron. Computer Systems: A Programmer’s Perspective.3rd Edition, Pearson, 2003. */
/*
 * mm_free - Freeing a block does nothing.
 */
void mm_free(void *ptr)
{
  size_t size = GET_SIZE(HDRP(ptr));
  add_free(ptr, size);
  PUT(HDRP(ptr), PACK(size, 0));
  PUT(FTRP(ptr), PACK(size, 0));

  coalesce(ptr);
}

/*
 * mm_realloc - Implemented simply in terms of mm_malloc and mm_free
 */
void *mm_realloc(void *ptr, size_t size)
{
  /*
   * ATTENTION: You do not need to implement realloc for this assignment
   */
  void *oldptr = ptr;
  void *newptr;
  size_t copySize;

  newptr = mm_malloc(size);
  if (newptr == NULL)
    return NULL;
  copySize = *(size_t *)((char *)oldptr - SIZE_T_SIZE);
  if (size < copySize)
    copySize = size;
  memcpy(newptr, oldptr, copySize);
  mm_free(oldptr);
  return newptr;
}