1 files changed, 93 insertions, 0 deletions
diff --git a/plugins/sid/sidplay-libs/resid/extfilt.cpp b/plugins/sid/sidplay-libs/resid/extfilt.cpp
new file mode 100644
index 00000000..461cdaf7
--- /dev/null
+++ b/plugins/sid/sidplay-libs/resid/extfilt.cpp
@@ -0,0 +1,93 @@
+//  ---------------------------------------------------------------------------
+//  This file is part of reSID, a MOS6581 SID emulator engine.
+//  Copyright (C) 2002  Dag Lem <resid@nimrod.no>
+//
+//  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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+//  ---------------------------------------------------------------------------
+
+#define __EXTFILT_CC__
+#include "extfilt.h"
+
+RESID_NAMESPACE_START
+
+// ----------------------------------------------------------------------------
+// Constructor.
+// ----------------------------------------------------------------------------
+ExternalFilter::ExternalFilter()
+{
+  reset();
+  enable_filter(true);
+  set_sampling_parameter(15915.6);
+  set_chip_model(MOS6581);
+}
+
+
+// ----------------------------------------------------------------------------
+// Enable filter.
+// ----------------------------------------------------------------------------
+void ExternalFilter::enable_filter(bool enable)
+{
+  enabled = enable;
+}
+
+
+// ----------------------------------------------------------------------------
+// Setup of the external filter sampling parameters.
+// ----------------------------------------------------------------------------
+void ExternalFilter::set_sampling_parameter(double pass_freq)
+{
+  static const double pi = 3.1415926535897932385;
+
+  // Low-pass:  R = 10kOhm, C = 1000pF; w0l = 1/RC = 1/(1e4*1e-9) = 100000
+  // High-pass: R =  1kOhm, C =   10uF; w0h = 1/RC = 1/(1e3*1e-5) =    100
+  // Multiply with 1.048576 to facilitate division by 1 000 000 by right-
+  // shifting 20 times (2 ^ 20 = 1048576).
+
+  //w0lp = 104858;
+  w0hp = 105;
+  w0lp = (sound_sample) (pass_freq * (2.0 * pi * 1.048576));
+}
+
+
+// ----------------------------------------------------------------------------
+// Set chip model.
+// ----------------------------------------------------------------------------
+void ExternalFilter::set_chip_model(chip_model model)
+{
+  if (model == MOS6581) {
+    // Maximum mixer DC output level; to be removed if the external
+    // filter is turned off: ((wave DC + voice DC)*voices + mixer DC)*volume
+    // See voice.cc and filter.cc for an explanation of the values.
+    mixer_DC = ((((0x800 - 0x380) + 0x800)*0xff*3 - 0xfff*0xff/18) >> 7)*0x0f;
+  }
+  else {
+    // No DC offsets in the MOS8580.
+    mixer_DC = 0;
+  }
+}
+
+
+// ----------------------------------------------------------------------------
+// SID reset.
+// ----------------------------------------------------------------------------
+void ExternalFilter::reset()
+{
+  // State of filter.
+  Vlp = 0;
+  Vhp = 0;
+  Vo = 0;
+}
+
+RESID_NAMESPACE_STOP