From 9c0e19a3be2288db79e2502e5fa450c3e20a668d Mon Sep 17 00:00:00 2001
From: Guenter  Geiger <ggeiger@users.sourceforge.net>
Date: Fri, 9 May 2003 16:04:00 +0000
Subject: This commit was generated by cvs2svn to compensate for changes in
 r610, which included commits to RCS files with non-trunk default branches.

svn path=/trunk/; revision=611
---
 pd/portaudio/pa_common/pa_dither.c | 91 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 pd/portaudio/pa_common/pa_dither.c

(limited to 'pd/portaudio/pa_common/pa_dither.c')

diff --git a/pd/portaudio/pa_common/pa_dither.c b/pd/portaudio/pa_common/pa_dither.c
new file mode 100644
index 00000000..10f43e69
--- /dev/null
+++ b/pd/portaudio/pa_common/pa_dither.c
@@ -0,0 +1,91 @@
+/*
+ * $Id: pa_dither.c,v 1.1.2.3 2002/06/16 13:11:02 rossbencina Exp $
+ * Portable Audio I/O Library triangular dither generator
+ *
+ * Based on the Open Source API proposed by Ross Bencina
+ * Copyright (c) 1999-2002 Phil Burk, Ross Bencina
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files
+ * (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * Any person wishing to distribute modifications to the Software is
+ * requested to send the modifications to the original developer so that
+ * they can be incorporated into the canonical version.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR
+ * ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
+ * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include "pa_dither.h"
+
+#define PA_DITHER_BITS_   (15)
+
+
+void PaUtil_InitializeTriangularDitherState( PaUtilTriangularDitherGenerator *state )
+{
+    state->previous = 0;
+    state->randSeed1 = 22222;
+    state->randSeed2 = 5555555;
+}
+
+
+signed long PaUtil_Generate16BitTriangularDither( PaUtilTriangularDitherGenerator *state )
+{
+    signed long current, highPass;
+
+    /* Generate two random numbers. */
+    state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
+    state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
+
+    /* Generate triangular distribution about 0.
+     * Shift before adding to prevent overflow which would skew the distribution.
+     * Also shift an extra bit for the high pass filter. 
+     */
+#define DITHER_SHIFT_  ((32 - PA_DITHER_BITS_) + 1)
+    current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
+              (((signed long)state->randSeed2)>>DITHER_SHIFT_);
+
+    /* High pass filter to reduce audibility. */
+    highPass = current - state->previous;
+    state->previous = current;
+    return highPass;
+}
+
+/* Multiply by PA_FLOAT_DITHER_SCALE_ to get a float between -2.0 and +1.99999 */
+#define PA_FLOAT_DITHER_SCALE_  (1.0f / ((1<<PA_DITHER_BITS_)-1))
+static const float const_float_dither_scale_ = PA_FLOAT_DITHER_SCALE_;
+
+float PaUtil_GenerateFloatTriangularDither( PaUtilTriangularDitherGenerator *state )
+{
+    signed long current, highPass;
+
+    /* Generate two random numbers. */
+    state->randSeed1 = (state->randSeed1 * 196314165) + 907633515;
+    state->randSeed2 = (state->randSeed2 * 196314165) + 907633515;
+
+    /* Generate triangular distribution about 0.
+     * Shift before adding to prevent overflow which would skew the distribution.
+     * Also shift an extra bit for the high pass filter. 
+     */
+#define DITHER_SHIFT_  ((32 - PA_DITHER_BITS_) + 1)
+    current = (((signed long)state->randSeed1)>>DITHER_SHIFT_) +
+              (((signed long)state->randSeed2)>>DITHER_SHIFT_);
+
+    /* High pass filter to reduce audibility. */
+    highPass = current - state->previous;
+    state->previous = current;
+    return ((float)highPass) * const_float_dither_scale_;
+}
-- 
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