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

#include <xen/types.h>

static void u32_swap(void *a, void *b, int size)
{
    u32 t = *(u32 *)a;
    *(u32 *)a = *(u32 *)b;
    *(u32 *)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: pointer to comparison function
 * @swap: pointer to swap function or NULL
 *
 * This function does a heapsort on the given array. You may provide a
 * swap 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)(const void *, const void *),
          void (*swap)(void *, void *, int size))
{
    /* pre-scale counters for performance */
    int i = (num/2) * size, n = num * size, c, r;

    if (!swap)
        swap = (size == 4 ? u32_swap : generic_swap);

    /* heapify */
    for ( ; i >= 0; i -= size )
    {
        for ( r = i; r * 2 < n; r  = c )
        {
            c = r * 2;
            if ( (c < n - size) && (cmp(base + c, base + c + size) < 0) )
                c += size;
            if ( cmp(base + r, base + c) >= 0 )
                break;
            swap(base + r, base + c, size);
        }
    }

    /* sort */
    for ( i = n - size; i >= 0; i -= size )
    {
        swap(base, base + i, size);
        for ( r = 0; r * 2 < i; r = c )
        {
            c = r * 2;
            if ( (c < i - size) && (cmp(base + c, base + c + size) < 0) )
                c += size;
            if ( cmp(base + r, base + c) >= 0 )
                break;
            swap(base + r, base + c, size);
        }
    }
}
