tools/time_smoother.c

   1
   2 // After looking at how pulseaudio is doing things,
   3 // i have came to the conclusion, that forgetting
   4 // about statistics is a bad idea ;)
   5 //
   6 // i am loosely basing this on pulsecore/time-smoother.c
   7
   8 #include "time_smoother.h"
   9 #include <stdlib.h>
  10 #include <assert.h>
  11
  12 time_smoother *time_smoother_new( int history_size )
  13 {
  14         time_smoother *retval = malloc( sizeof( time_smoother ) );
  15         if( !retval )
  16                 return NULL;
  17
  18         retval->x = malloc( sizeof(jack_nframes_t) * history_size );
  19
  20         if( !retval->x ) {
  21                 free( retval );
  22                 return NULL;
  23         }
  24
  25         retval->y = malloc( sizeof(jack_nframes_t) * history_size );
  26         if( !retval->y ) {
  27                 free( retval->x );
  28                 free( retval );
  29                 return NULL;
  30         }
  31
  32         retval->history_size = history_size;
  33         retval->num_valid = 0;
  34         return retval;
  35 }
  36
  37 void time_smoother_free( time_smoother *ts )
  38 {
  39         free( ts->x );
  40         free( ts->y );
  41         free( ts );
  42 }
  43
  44 // put a time measurement into the smoother.
  45 // assume monotonically increasing x.
  46
  47 void time_smoother_put ( time_smoother *ts, jack_nframes_t x, jack_nframes_t y )
  48 {
  49         int i;
  50         int oldest_index;
  51         jack_nframes_t oldest_diff;
  52
  53         if( ts->num_valid < ts->history_size ) {
  54                 ts->x[ts->num_valid] = x;
  55                 ts->y[ts->num_valid] = y;
  56                 ts->num_valid += 1;
  57                 return;
  58         }
  59
  60         // Its full. find oldest value and replace.
  61         oldest_index = -1;
  62         oldest_diff  = 0;
  63         for( i=0; i<ts->history_size; i++ ) {
  64                 if( (x - ts->x[i]) > oldest_diff ) {
  65                         oldest_diff  = (x - ts->x[i]);
  66                         oldest_index = i;
  67                 }
  68         }
  69         assert( oldest_index != -1 );
  70
  71         ts->x[oldest_index] = x;
  72         ts->y[oldest_index] = y;
  73 }
  74
  75 // return a and b for the linear regression line,
  76 // such that y=a+bx;
  77 void time_smoother_get_linear_params( time_smoother *ts,
  78                                       jack_nframes_t now_x,
  79                                       jack_nframes_t now_y,
  80                                       jack_nframes_t history,
  81                                       double *a, double *b    )
  82 {
  83         int i;
  84         jack_nframes_t sum_x = 0;
  85         jack_nframes_t sum_y = 0;
  86         int num_values = 0;
  87         double mean_x, mean_y;
  88         double sxx = 0.0;
  89         double sxy = 0.0;
  90         double val_a, val_b;
  91
  92         for( i=0; i<ts->num_valid; i++ ) {
  93                 if( (now_x - ts->x[i]) < history ) {
  94                         sum_x += (now_x - ts->x[i]);
  95                         sum_y += (now_y - ts->y[i]);
  96                         num_values += 1;
  97                 }
  98         }
  99
 100         // Give some valid values if we dont have
 101         // enough data;
 102         if( num_values < 10 ) {
 103                 if( a ) *a = 0.0;
 104                 if( b ) *b = 1.0;
 105
 106                 return;
 107         }
 108
 109         mean_x = (double) sum_x / (double) num_values;
 110         mean_y = (double) sum_y / (double) num_values;
 111         //printf( "mean: %f %f\n", (float) mean_x, (float) mean_y );
 112
 113         for( i=0; i<ts->num_valid; i++ ) {
 114                 if( (now_x - ts->x[i]) < history ) {
 115                         sxx += ((double)(now_x-ts->x[i])-mean_x) * ((double)(now_x-ts->x[i])-mean_x);
 116                         sxy += ((double)(now_x-ts->x[i])-mean_x) * ((double)(now_y-ts->y[i])-mean_y);
 117                 }
 118         }
 119
 120         val_b = sxy/sxx;
 121         val_a = mean_y - val_b*mean_x;
 122
 123         if( a )
 124                 *a = val_a;
 125
 126         if( b )
 127                 *b = val_b;
 128 }