X-Git-Url: https://git.carlh.net/gitweb/?a=blobdiff_plain;f=libs%2Fardour%2Finterpolation.cc;h=bccaa45553484bb0eceb9e82eeb6b578a3b174a4;hb=06cc5e5240cc2bfeb4e22c742a5705566bd11dbe;hp=7dcc1b7ccbfab551c28c8c3197b09ec3464b9c6c;hpb=62e730b57ab30bb8642c5682b53b7c534d923a24;p=ardour.git

diff --git a/libs/ardour/interpolation.cc b/libs/ardour/interpolation.cc
index 7dcc1b7ccb..bccaa45553 100644
--- a/libs/ardour/interpolation.cc
+++ b/libs/ardour/interpolation.cc
@@ -1,3 +1,22 @@
+/*
+    Copyright (C) 2012 Paul Davis 
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
 #include <stdint.h>
 #include <cstdio>
 
@@ -10,21 +29,18 @@ framecnt_t
 LinearInterpolation::interpolate (int channel, framecnt_t nframes, Sample *input, Sample *output)
 {
 	// index in the input buffers
-	framecnt_t   i = 0;
+	framecnt_t i = 0;
 
-	double acceleration;
-	double distance = 0.0;
+	double acceleration = 0;
 
 	if (_speed != _target_speed) {
 		acceleration = _target_speed - _speed;
-	} else {
-		acceleration = 0.0;
 	}
 
-	distance = phase[channel];
 	for (framecnt_t outsample = 0; outsample < nframes; ++outsample) {
-		i = floor(distance);
-		Sample fractional_phase_part = distance - i;
+		double const d = phase[channel] + outsample * (_speed + acceleration);
+		i = floor(d);
+		Sample fractional_phase_part = d - i;
 		if (fractional_phase_part >= 1.0) {
 			fractional_phase_part -= 1.0;
 			i++;
@@ -36,12 +52,11 @@ LinearInterpolation::interpolate (int channel, framecnt_t nframes, Sample *input
 				input[i] * (1.0f - fractional_phase_part) +
 				input[i+1] * fractional_phase_part;
 		}
-		distance += _speed + acceleration;
 	}
 
+	double const distance = phase[channel] + nframes * (_speed + acceleration);
 	i = floor(distance);
-	phase[channel] = distance - floor(distance);
-
+	phase[channel] = distance - i;
 	return i;
 }
 
@@ -73,13 +88,13 @@ CubicInterpolation::interpolate (int channel, framecnt_t nframes, Sample *input,
     }
 
     /* 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: 
+		    /* 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]);
@@ -106,7 +121,7 @@ CubicInterpolation::interpolate (int channel, framecnt_t nframes, Sample *input,
 		    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
@@ -120,17 +135,18 @@ CubicInterpolation::interpolate (int channel, framecnt_t nframes, Sample *input,
 		    inm1 = input[i];
 	    }
 
-    } else {
-
-	    /* not sure that this is ever utilized - it implies that one of the input/output buffers is missing */
+	    i = floor(distance);
+	    phase[channel] = distance - floor(distance);
 
+    } else {
+	    /* used to calculate play-distance with acceleration (silent roll)
+	     * (use same algorithm as real playback for identical rounding/floor'ing)
+	     */
 	    for (framecnt_t outsample = 0; outsample < nframes; ++outsample) {
 		    distance += _speed + acceleration;
 	    }
+	    i = floor(distance);
     }
 
-    i = floor(distance);
-    phase[channel] = distance - floor(distance);
-
     return i;
 }