libs/ardour/interpolation.cc

   1 #include <stdint.h>
   2 #include <cstdio>
   3
   4 #include "ardour/interpolation.h"
   5
   6 using namespace ARDOUR;
   7
   8
   9 framecnt_t
  10 LinearInterpolation::interpolate (int channel, framecnt_t nframes, Sample *input, Sample *output)
  11 {
  12         // index in the input buffers
  13         framecnt_t i = 0;
  14
  15         double acceleration = 0;
  16
  17         if (_speed != _target_speed) {
  18                 acceleration = _target_speed - _speed;
  19         }
  20
  21         for (framecnt_t outsample = 0; outsample < nframes; ++outsample) {
  22                 double const d = phase[channel] + outsample * (_speed + acceleration);
  23                 i = floor(d);
  24                 Sample fractional_phase_part = d - i;
  25                 if (fractional_phase_part >= 1.0) {
  26                         fractional_phase_part -= 1.0;
  27                         i++;
  28                 }
  29
  30                 if (input && output) {
  31                 // Linearly interpolate into the output buffer
  32                         output[outsample] =
  33                                 input[i] * (1.0f - fractional_phase_part) +
  34                                 input[i+1] * fractional_phase_part;
  35                 }
  36         }
  37
  38         double const distance = phase[channel] + nframes * (_speed + acceleration);
  39         i = floor(distance);
  40         phase[channel] = distance - i;
  41         return i;
  42 }
  43
  44 framecnt_t
  45 CubicInterpolation::interpolate (int channel, framecnt_t nframes, Sample *input, Sample *output)
  46 {
  47     // index in the input buffers
  48     framecnt_t   i = 0;
  49
  50     double acceleration;
  51     double distance = 0.0;
  52
  53     if (_speed != _target_speed) {
  54         acceleration = _target_speed - _speed;
  55     } else {
  56             acceleration = 0.0;
  57     }
  58
  59     distance = phase[channel];
  60
  61     if (nframes < 3) {
  62             /* no interpolation possible */
  63
  64             for (i = 0; i < nframes; ++i) {
  65                     output[i] = input[i];
  66             }
  67
  68             return nframes;
  69     }
  70
  71     /* keep this condition out of the inner loop */
  72
  73     if (input && output) {
  74
  75             Sample inm1;
  76
  77             if (floor (distance) == 0.0) {
  78                     /* best guess for the fake point we have to add to be able to interpolate at i == 0:
  79                        .... maintain slope of first actual segment ...
  80                     */
  81                     inm1 = input[i] - (input[i+1] - input[i]);
  82             } else {
  83                     inm1 = input[i-1];
  84             }
  85
  86             for (framecnt_t outsample = 0; outsample < nframes; ++outsample) {
  87
  88                     float f = floor (distance);
  89                     float fractional_phase_part = distance - f;
  90
  91                     /* get the index into the input we should start with */
  92
  93                     i = lrintf (f);
  94
  95                     /* fractional_phase_part only reaches 1.0 thanks to float imprecision. In theory
  96                        it should always be < 1.0. If it ever >= 1.0, then bump the index we use
  97                        and back it off. This is the point where we "skip" an entire sample in the
  98                        input, because the phase part has accumulated so much error that we should
  99                        really be closer to the next sample. or something like that ...
 100                     */
 101
 102                     if (fractional_phase_part >= 1.0) {
 103                             fractional_phase_part -= 1.0;
 104                             ++i;
 105                     }
 106
 107                     // Cubically interpolate into the output buffer: keep this inlined for speed and rely on compiler
 108                     // optimization to take care of the rest
 109                     // shamelessly ripped from Steve Harris' swh-plugins (ladspa-util.h)
 110
 111                     output[outsample] = input[i] + 0.5f * fractional_phase_part * (input[i+1] - inm1 +
 112                                                           fractional_phase_part * (4.0f * input[i+1] + 2.0f * inm1 - 5.0f * input[i] - input[i+2] +
 113                                                                 fractional_phase_part * (3.0f * (input[i] - input[i+1]) - inm1 + input[i+2])));
 114
 115                     distance += _speed + acceleration;
 116                     inm1 = input[i];
 117             }
 118
 119     } else {
 120
 121             /* not sure that this is ever utilized - it implies that one of the input/output buffers is missing */
 122
 123             for (framecnt_t outsample = 0; outsample < nframes; ++outsample) {
 124                     distance += _speed + acceleration;
 125             }
 126     }
 127
 128     i = floor(distance);
 129     phase[channel] = distance - floor(distance);
 130
 131     return i;
 132 }