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/* ************************************************************************** */
/* */
/* ::: :::::::: */
/* ft_mergesort.c :+: :+: :+: */
/* +:+ +:+ +:+ */
/* By: cacharle <marvin@42.fr> +#+ +:+ +#+ */
/* +#+#+#+#+#+ +#+ */
/* Created: 2020/02/10 02:26:41 by cacharle #+# #+# */
/* Updated: 2020/04/04 22:40:55 by charles ### ########.fr */
/* */
/* ************************************************************************** */
#include "libft_algo.h"
/*
** \brief Helper function to return in case of error
** \param left Left subarray
** \param right Right subarray
** \return -1 to indicate error
*/
static int st_mergesort_error(void *left, void *right)
{
free(left);
free(right);
return (-1);
}
/*
** \brief Merge 2 sorted arrays
** \param arrays Struct containing the arrays (base, left, right)
** \param nel Number of element in base
** \param compar Comparison function
*/
static void st_merge_sorted(struct s_merge_sorted_arrays *arrays, size_t nel,
size_t width, int (*compar)(const void *, const void *))
{
size_t bi;
size_t li;
size_t ri;
size_t mid;
mid = nel / 2;
bi = 0;
li = 0;
ri = 0;
while (li < mid && ri < nel - mid)
{
if (compar(arrays->left + li * width, arrays->right + ri * width) < 0)
ft_memcpy(arrays->base + bi * width,
arrays->left + li++ * width, width);
else
ft_memcpy(arrays->base + bi * width,
arrays->right + ri++ * width, width);
bi++;
}
while (li < mid)
ft_memcpy(arrays->base + bi++ * width,
arrays->left + li++ * width, width);
while (ri < nel - mid)
ft_memcpy(arrays->base + bi++ * width,
arrays->right + ri++ * width, width);
}
/*
** \brief Sort an array using the merge sort algorithm
** \param base Array to sort
** \param nel Number of element in the array
** \param width Size of each element
** \return 0 on success, -1 on error
*/
int ft_mergesort(void *base, size_t nel, size_t width,
int (*compar)(const void *, const void *))
{
size_t mid;
struct s_merge_sorted_arrays arrays;
if (nel < 2)
return (0);
mid = nel / 2;
if ((arrays.left = malloc(mid * width)) == NULL)
return (-1);
if ((arrays.right = malloc((nel - mid) * width)) == NULL)
return (st_mergesort_error(arrays.left, NULL));
ft_memcpy(arrays.left, base, mid * width);
ft_memcpy(arrays.right, base + mid * width, (nel - mid) * width);
if (ft_mergesort(arrays.left, mid, width, compar) == -1)
return (st_mergesort_error(arrays.left, arrays.right));
if (ft_mergesort(arrays.right, nel - mid, width, compar) == -1)
return (st_mergesort_error(arrays.left, arrays.right));
arrays.base = base;
st_merge_sorted(&arrays, nel, width, compar);
free(arrays.left);
free(arrays.right);
return (0);
}
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