/*
 * 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 <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

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

/*********************************************************
 * NOTE TO STUDENTS: Before you do anything else, please
 * provide your team information in the following struct.
 ********************************************************/
team_t team = {
    /* Team name */
    "Saltedfish team",
    /* First member's full name */
    "Yue Pan",
    /* First member's email address */
    "zxc479773533@gmail.com",
    /* Second member's full name (leave blank if none) */
    "",
    /* Second member's email address (leave blank if none) */
    ""};

/* 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)))

/* basic contants and macros */
#define WSIZE 4  /* Word and header/footer size (bytes) */
#define DSIZE 8  /* Double word size (bytes) */
#define CHUNKSIZE (1 << 12)  /* Exrend heap by this amount (bytes) */

#define MAX(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 adress 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)))

/* Prologue block */
static char *heap_listp;

/* Function prototypes */
static void *extend_heap(size_t words);
static void *coalesce(void *bp);
static void *find_fit(size_t asize);
static void place(void *bp, size_t asize);

/*
 * extend_heap - extend heap and get a bp
 */
static void *extend_heap(size_t words) {
	char *bp;
	size_t size;

	size = (words % 2) ? (words + 1) * WSIZE : words * WSIZE;
	if ((long)(bp = mem_sbrk(size)) == -1)
		return NULL;

	PUT(HDRP(bp), PACK(size, 0));
	PUT(FTRP(bp), PACK(size, 0));
	PUT(HDRP(NEXT_BLKP(bp)), PACK(0, 1));

	return coalesce(bp);
}

/*
 * coalesce - coalesce the bps
 */
static void *coalesce(void *bp) {
	size_t prev_alloc = GET_ALLOC(FTRP(PREV_BLKP(bp)));
	size_t next_alloc = GET_ALLOC(HDRP(NEXT_BLKP(bp)));
  size_t size = GET_SIZE(HDRP(bp));

  /* Case 1: */
  if (prev_alloc && next_alloc) {
    return bp;
  }

  /* Case 2: */
  else if (prev_alloc && !next_alloc) {
    size += GET_SIZE(HDRP(NEXT_BLKP(bp)));
    PUT(HDRP(bp), PACK(size, 0));
    PUT(FTRP(bp), PACK(size, 0));
  }

  /* Case 3: */
  else if (!prev_alloc && next_alloc) {
    size += GET_SIZE(FTRP(PREV_BLKP(bp)));
    PUT(FTRP(bp), PACK(size, 0));
    PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
    bp = PREV_BLKP(bp);
  }

  /* Case 4: */
  else if (!prev_alloc && !prev_alloc) {
    size += GET_SIZE(HDRP(PREV_BLKP(bp))) + GET_SIZE(FTRP(NEXT_BLKP(bp)));
    PUT(HDRP(PREV_BLKP(bp)), PACK(size, 0));
    PUT(FTRP(NEXT_BLKP(bp)), PACK(size, 0));
    bp = PREV_BLKP(bp);
  }

  return bp;
}

/*
 * find_fit - find a fit chunk
 */
static void *find_fit(size_t asize) {
  char *bp = heap_listp;
  while (GET_SIZE(HDRP(bp)) > 0) {
    if (GET_ALLOC(HDRP(bp)) == 0 && GET_SIZE(HDRP(bp)) >= asize)
      return bp;
    bp = NEXT_BLKP(bp);
  }
  return NULL;
}

/*
 * place - set chunk
 */
static void place(void *bp, size_t asize) {
  size_t csize = GET_SIZE(HDRP(bp));

  if ((csize - asize) >= (2 * DSIZE)) {
    PUT(HDRP(bp), PACK(asize, 1));
    PUT(FTRP(bp), PACK(asize, 1));
    bp = NEXT_BLKP(bp);
    PUT(HDRP(bp), PACK(csize - asize, 0));
    PUT(FTRP(bp), PACK(csize - asize, 0));
  }
  else {
    PUT(HDRP(bp), PACK(csize, 1));
    PUT(FTRP(bp), PACK(csize, 1));
  }
}

/*
 * mm_init - initialize the malloc package.
 */
int mm_init(void) {
	if ((heap_listp = mem_sbrk(4 * WSIZE)) == (void*)(-1))
		return -1;

	PUT(heap_listp, 0);
	PUT(heap_listp + (1 * WSIZE), PACK(DSIZE, 1));
	PUT(heap_listp + (2 * WSIZE), PACK(DSIZE, 1));
	PUT(heap_listp + (3 * WSIZE), PACK(0, 1));
	heap_listp += 2 * WSIZE;

	if (extend_heap(CHUNKSIZE/WSIZE) == NULL)
    return -1;
	return 0;
}

/*
 * 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;
  size_t extendsize;
  char *bp;

  if (size == 0)
    return NULL;
  
  if (size <= DSIZE)
    asize = 2 * DSIZE;
  else
    asize = DSIZE * ((size + (DSIZE) + (DSIZE - 1)) / DSIZE);

  if ((bp = find_fit(asize)) != NULL) {
    place(bp, asize);
    return bp;
  }

  extendsize = MAX(asize, CHUNKSIZE);
  if ((bp = extend_heap(extendsize / WSIZE)) == NULL)
    return NULL;
  place(bp, asize);

  return bp;
}

/*
 * mm_free - Freeing a block does nothing.
 */
void mm_free(void *ptr) {
  size_t size = GET_SIZE(HDRP(ptr));

  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) {
  size_t ptr_size;
  char *bp;

  if (ptr == NULL)
    return mm_malloc(size);

  else if (size == 0) {
    mm_free(ptr);
    return 0;
  }

  else {
    if ((bp = mm_malloc(size)) == NULL)
      return 0;
    ptr_size = GET_SIZE(HDRP(ptr));
    if (ptr_size >= size)
      memcpy(bp, ptr, size);
    else
      memcpy(bp, ptr, ptr_size);
    mm_free(ptr);
    return bp;
  }
}
