I have implemented a Moving Median Filter and I would like a review.

Header

/**
* Moving Median Filter.
*
* This algorithm is iterative. Each call will compute the next point.
* In the example below, the kernel has a size of 3. Notice that the
* values in the kernel are alway sorted. The left value is therefore
* the minimum in the kernel, the center value is the median and the
* right value is the maximum value.
*
* Input data:         0 1 2 5 4 8 3
* Kernel:      |0 0 0|            .   (min=0, med=0, max=0)
*                |0 0 0|          .   (min=0, med=0, max=0)
*                  |0 0 1|        .   (min=0, med=0, max=1)
*                    |0 1 2|      .   (min=0, med=1, max=2)
*                      |1 2 5|    .   (min=1, med=2, max=5)
*                        |2 4 5|  .   (min=2, med=4, max=5)
*                          |4 5 8|.   (min=4, med=5, max=8)
*                            |3 4 8|  (min=3, med=4, max=8)
*/
#pragma once
#include <stdlib.h>

typedef struct MedfiltNode {
    float value;
    size_t index; // Node index in the sorted table
    struct MedfiltNode* parent;
    struct MedfiltNode* sorted;
} MedfiltNode;

typedef struct MedfiltData {
    MedfiltNode *kernel; // Working filter memory
    MedfiltNode *oldest; // Reference to the oldest value in the kernel
    size_t length; // Number of nodes
} MedfiltData;

void median_init(MedfiltData *data, MedfiltNode *nodes, size_t length);
void median(float input, MedfiltData *data, float *median, float *min, float *max);

Source Code

/**
 * Moving Median Filter.
 * @author CHEVALLIER Yves <[email protected]>
 */
#include <stdint.h>
#include <stdlib.h>
#include "medfilt.h"

static void swap(MedfiltNode **a, MedfiltNode **b)
{
    // Swap two node references in the sorted table.
    MedfiltNode *temp = *a;
    *a = *b;
    *b = temp;

    // Preserve index. Used to retrive the node position in the sorted table.
    size_t index = (*a)->index;
    (*a)->index = (*b)->index;
    (*b)->index = index;
}

void median(float input, MedfiltData *data, float *median, float *min, float *max)
{
    // New value replaces the oldest
    MedfiltNode *n = data->kernel;
    MedfiltNode *node = data->oldest;
    node->value = input;
    data->oldest = node->parent;

    // Sort the kernel
    #define VAL(x) (n[x].sorted->value)
    for (size_t i = node->index; i < data->length - 1 && VAL(i) > VAL(i + 1); i++) {
        swap(&n[i].sorted, &n[i + 1].sorted);
    }

    for (size_t i = node->index; i > 0 && VAL(i) < VAL(i - 1); i++) {
        swap(&n[i].sorted, &n[i - 1].sorted);
    }

    // Get kernel information from sorted entries
    *min = n[0].sorted->value;
    *max = n[data->length - 1].sorted->value;
    *median = n[data->length / 2].sorted->value;
}

void median_init(MedfiltData *data, MedfiltNode *nodes, size_t length)
{
    data->kernel = nodes;
    data->length = length;

    // Linked list initialization
    data->oldest = &data->kernel[length - 1];
    for (size_t i = 0; i < length; data->oldest = &data->kernel[i], i++) {
        data->kernel[i] = (MedfiltNode) {
            .value = 0,
            .parent = data->oldest,
            .index = i,
            .sorted = &data->kernel[i]
        };
    }
}