X-Git-Url: https://main.carlh.net/gitweb/?a=blobdiff_plain;f=libs%2Fardour%2Finterpolation.cc;h=bccaa45553484bb0eceb9e82eeb6b578a3b174a4;hb=be6d6231fbe56875815c81999e1fc41db0e21a23;hp=20ab584885e7f19dd6bd348c2648b5d429c08c1b;hpb=a473d630eb165272992e90f8d854b1d66ec0be63;p=ardour.git

diff --git a/libs/ardour/interpolation.cc b/libs/ardour/interpolation.cc
index 20ab584885..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;
 }
 
@@ -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;
 }