filtering.c

   1 #include <stdlib.h>
   2 #include <hardware/sensors.h>
   3 #include <math.h>
   4 #include <pthread.h>
   5 #include <utils/Log.h>
   6 #include "common.h"
   7 #include "filtering.h"
   8
   9
  10 struct filter_median
  11 {
  12         float* buff;
  13         unsigned int idx;
  14         unsigned int count;
  15         unsigned int sample_size;
  16 };
  17
  18 static unsigned int partition(float* list, unsigned int left,
  19         unsigned int right, unsigned int pivot_index)
  20 {
  21         unsigned int i;
  22         unsigned int store_index = left;
  23         float aux;
  24         float pivot_value = list[pivot_index];
  25
  26         // swap list[pivotIndex] and list[right]
  27         aux = list[pivot_index];
  28         list[pivot_index] = list[right];
  29         list[right] = aux;
  30
  31         for (i = left; i < right; i++)
  32         {
  33                 if (list[i] < pivot_value)
  34                 {
  35                         // swap list[store_index] and list[i]
  36                         aux = list[store_index];
  37                         list[store_index] = list[i];
  38                         list[i] = aux;
  39                         store_index++;
  40                 }
  41         }
  42         //swap list[right] and list[store_index]
  43         aux = list[right];
  44         list[right] = list[store_index];
  45         list[store_index] = aux;
  46         return store_index;
  47 }
  48
  49 /* http://en.wikipedia.org/wiki/Quickselect */
  50 float median(float* queue, unsigned int size)
  51 {
  52         unsigned int left = 0;
  53         unsigned int right = size - 1;
  54         unsigned int pivot_index;
  55         unsigned int median_index = (right / 2);
  56         float temp[size];
  57
  58         memcpy(temp, queue, size * sizeof(float));
  59
  60         /* If the list has only one element return it */
  61         if (left == right)
  62                 return temp[left];
  63
  64         while (left < right) {
  65                 pivot_index = (left + right) / 2;
  66                 pivot_index = partition(temp, left, right, pivot_index);
  67                 if (pivot_index == median_index)
  68                         return temp[median_index];
  69                 else if (pivot_index > median_index)
  70                         right = pivot_index - 1;
  71                 else
  72                         left = pivot_index + 1;
  73         }
  74
  75         return temp[left];
  76 }
  77
  78 void denoise_median_init(int s, unsigned int num_fields,
  79         unsigned int max_samples)
  80 {
  81         struct filter_median* f_data = (struct filter_median*) calloc(1, sizeof(struct filter_median));
  82         f_data->buff = (float*)calloc(max_samples,
  83                 sizeof(float) * num_fields);
  84         f_data->sample_size = max_samples;
  85         f_data->count = 0;
  86         f_data->idx = 0;
  87         sensor_info[s].filter = f_data;
  88 }
  89
  90 void denoise_median_release(int s)
  91 {
  92         if (!sensor_info[s].filter)
  93                 return;
  94
  95         free(((struct filter_median*)sensor_info[s].filter)->buff);
  96         free(sensor_info[s].filter);
  97         sensor_info[s].filter = NULL;
  98 }
  99 void denoise_median(struct sensor_info_t* info, struct sensors_event_t* data,
 100                                         unsigned int num_fields)
 101 {
 102         float x, y, z;
 103         float scale;
 104         unsigned int field, offset;
 105
 106         struct filter_median* f_data = (struct filter_median*) info->filter;
 107         if (!f_data)
 108                 return;
 109
 110
 111         if (f_data->count < f_data->sample_size)
 112                 f_data->count++;
 113
 114         for (field = 0; field < num_fields; field++) {
 115                 offset = f_data->sample_size * field;
 116                 f_data->buff[offset + f_data->idx] = data->data[field];
 117
 118                 data->data[field] = median(f_data->buff + offset, f_data->count);
 119         }
 120
 121         f_data->idx = (f_data->idx + 1) % f_data->sample_size;
 122 }
 123