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fix conceptually broken cubic interpolator that failed to handle the i=0 case, and don't rely on inlining for speed there

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git-svn-id: svn://localhost/ardour2/branches/3.0@5792 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Paul Davis 2009-10-16 19:53:25 +00:00
parent 4650d86312
commit 69be1aa7bf
2 changed files with 64 additions and 24 deletions
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12
libs/ardour/ardour/interpolation.h
View file

@ -39,23 +39,11 @@ class Interpolation {
};
class LinearInterpolation : public Interpolation {
protected:
public:
nframes_t interpolate (int channel, nframes_t nframes, Sample* input, Sample* output);
};
class CubicInterpolation : public Interpolation {
protected:
// shamelessly ripped from Steve Harris' swh-plugins (ladspa-util.h)
static inline float cube_interp(const float fr, const float inm1, const float
in, const float inp1, const float inp2)
{
return in + 0.5f * fr * (inp1 - inm1 +
fr * (4.0f * inp1 + 2.0f * inm1 - 5.0f * in - inp2 +
fr * (3.0f * (in - inp1) - inm1 + inp2)));
}
public:
nframes_t interpolate (int channel, nframes_t nframes, Sample* input, Sample* output);
};

76
libs/ardour/interpolation.cc
View file

@ -61,19 +61,71 @@ CubicInterpolation::interpolate (int channel, nframes_t nframes, Sample *input,
}
distance = phase[channel];
for (nframes_t outsample = 0; outsample < nframes; ++outsample) {
i = floor(distance);
Sample fractional_phase_part = distance - i;
if (fractional_phase_part >= 1.0) {
fractional_phase_part -= 1.0;
i++;
}
if (input && output) {
// Cubically interpolate into the output buffer
output[outsample] = cube_interp(fractional_phase_part, input[i-1], input[i], input[i+1], input[i+2]);
}
distance += _speed + acceleration;
if (nframes < 3) {
/* no interpolation possible */
for (i = 0; i < nframes; ++i) {
output[i] = input[i];
}
return nframes;
}
/* keep this condition out of the inner loop */
if (input && output) {
Sample inm1;
if (floor (distance) == 0.0) {
/* best guess for the fake point we have to add to be able to interpolate at i == 0:
.... maintain slope of first actual segment ...
*/
inm1 = input[i] - (input[i+1] - input[i]);
} else {
inm1 = input[i-1];
}
for (nframes_t outsample = 0; outsample < nframes; ++outsample) {
float f = floor (distance);
float fractional_phase_part = distance - f;
/* get the index into the input we should start with */
i = lrintf (f);
/* fractional_phase_part only reaches 1.0 thanks to float imprecision. In theory
it should always be < 1.0. If it ever >= 1.0, then bump the index we use
and back it off. This is the point where we "skip" an entire sample in the
input, because the phase part has accumulated so much error that we should
really be closer to the next sample. or something like that ...
*/
if (fractional_phase_part >= 1.0) {
fractional_phase_part -= 1.0;
++i;
}
// Cubically interpolate into the output buffer: keep this inlined for speed and rely on compiler
// optimization to take care of the rest
// shamelessly ripped from Steve Harris' swh-plugins (ladspa-util.h)
output[outsample] = input[i] + 0.5f * fractional_phase_part * (input[i+1] - inm1 +
fractional_phase_part * (4.0f * input[i+1] + 2.0f * inm1 - 5.0f * input[i] - input[i+2] +
fractional_phase_part * (3.0f * (input[i] - input[i+1]) - inm1 + input[i+2])));
distance += _speed + acceleration;
}
} else {
/* not sure that this is ever utilized - it implies that one of the input/output buffers is missing */
for (nframes_t outsample = 0; outsample < nframes; ++outsample) {
distance += _speed + acceleration;
}
}
i = floor(distance);