/*
   * A fast, small, non-recursive O(nlog n) sort for the Linux kernel
   *
   * Jan 23 2005  Matt Mackall <mpm@selenic.com>
   */

  #include <linux/types.h>
  #include <linux/export.h>

  #include <linux/sort.h>

  static int alignment_ok(const void *base, int align)
  {
  	return IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) ||
  		((unsigned long)base & (align - 1)) == 0;
  }

  static void u32_swap(void *a, void *b, int size)

  {
  	u32 t = *(u32 *)a;
  	*(u32 *)a = *(u32 *)b;
  	*(u32 *)b = t;
  }

  static void u64_swap(void *a, void *b, int size)
  {
  	u64 t = *(u64 *)a;
  	*(u64 *)a = *(u64 *)b;
  	*(u64 *)b = t;
  }

  static void generic_swap(void *a, void *b, int size)

  {
  	char t;
  
  	do {
  		t = *(char *)a;
  		*(char *)a++ = *(char *)b;
  		*(char *)b++ = t;
  	} while (--size > 0);
  }

  /**

   * sort - sort an array of elements
   * @base: pointer to data to sort
   * @num: number of elements
   * @size: size of each element

   * @cmp_func: pointer to comparison function
   * @swap_func: pointer to swap function or NULL

   *
   * This function does a heapsort on the given array. You may provide a

   * swap_func function optimized to your element type.

   *
   * Sorting time is O(n log n) both on average and worst-case. While
   * qsort is about 20% faster on average, it suffers from exploitable
   * O(n*n) worst-case behavior and extra memory requirements that make
   * it less suitable for kernel use.
   */
  
  void sort(void *base, size_t num, size_t size,

  	  int (*cmp_func)(const void *, const void *),
  	  void (*swap_func)(void *, void *, int size))

  {
  	/* pre-scale counters for performance */

  	int i = (num/2 - 1) * size, n = num * size, c, r;

  	if (!swap_func) {
  		if (size == 4 && alignment_ok(base, 4))
  			swap_func = u32_swap;
  		else if (size == 8 && alignment_ok(base, 8))
  			swap_func = u64_swap;
  		else
  			swap_func = generic_swap;
  	}

  
  	/* heapify */
  	for ( ; i >= 0; i -= size) {

  		for (r = i; r * 2 + size < n; r  = c) {
  			c = r * 2 + size;

  			if (c < n - size &&
  					cmp_func(base + c, base + c + size) < 0)

  				c += size;

  			if (cmp_func(base + r, base + c) >= 0)

  				break;

  			swap_func(base + r, base + c, size);

  		}
  	}
  
  	/* sort */

  	for (i = n - size; i > 0; i -= size) {

  		swap_func(base, base + i, size);

  		for (r = 0; r * 2 + size < i; r = c) {
  			c = r * 2 + size;

  			if (c < i - size &&
  					cmp_func(base + c, base + c + size) < 0)

  				c += size;

  			if (cmp_func(base + r, base + c) >= 0)

  				break;

  			swap_func(base + r, base + c, size);

  		}
  	}
  }
  
  EXPORT_SYMBOL(sort);
  
  #if 0

  #include <linux/slab.h>

  /* a simple boot-time regression test */
  
  int cmpint(const void *a, const void *b)
  {
  	return *(int *)a - *(int *)b;
  }
  
  static int sort_test(void)
  {

  	int *a, i, r = 1;

  
  	a = kmalloc(1000 * sizeof(int), GFP_KERNEL);
  	BUG_ON(!a);
  
  	printk("testing sort()
  ");
  
  	for (i = 0; i < 1000; i++) {
  		r = (r * 725861) % 6599;
  		a[i] = r;
  	}
  
  	sort(a, 1000, sizeof(int), cmpint, NULL);
  
  	for (i = 0; i < 999; i++)
  		if (a[i] > a[i+1]) {
  			printk("sort() failed!
  ");
  			break;
  		}
  
  	kfree(a);
  
  	return 0;
  }
  
  module_init(sort_test);
  #endif