Merge branch 'dfsg-orig'

[debian/gnuradio] / gr-atsc / src / lib / atsci_sliding_correlator.cc

diff --git a/gr-atsc/src/lib/atsci_sliding_correlator.cc b/gr-atsc/src/lib/atsci_sliding_correlator.cc
new file mode 100644 (file)
index 0000000..bde8022
--- /dev/null
+++ b/gr-atsc/src/lib/atsci_sliding_correlator.cc
@@ -0,0 +1,90 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2002,2006 Free Software Foundation, Inc.
+ * 
+ * This file is part of GNU Radio
+ * 
+ * GNU Radio 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 3, or (at your option)
+ * any later version.
+ * 
+ * GNU Radio 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 GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include <atsci_sliding_correlator.h>
+#include <atsci_pnXXX.h>
+
+// #define TRY_BACKWARDS
+
+/*
+ * Return the number of 1's in v.
+ * This magic code is explained wonderfully in the AMD Athlon
+ * optimization guide, pg 136.
+ */
+static inline int popcount32 (unsigned long v)
+{
+  unsigned long w = v - ((v >> 1) & 0x55555555);
+  unsigned long x = (w & 0x33333333) + ((w >> 2) & 0x33333333);
+  unsigned long y = (x + (x >> 4)) & 0x0f0f0f0f;
+  unsigned long z = (y * 0x01010101) >> 24;
+
+  return z;
+}
+
+atsci_sliding_correlator::atsci_sliding_correlator ()
+{
+#if defined(TRY_BACKWARDS)
+  for (int i = 511 - 1; i >= 0; i--)
+    mask.shift_in (atsc_pn511[i]);
+#else
+  for (unsigned i = 0; i < 511; i++)
+    mask.shift_in (atsc_pn511[i]);
+#endif
+
+  and_mask.shift_in (0);
+  for (int i = 0; i < 511; i++)
+    and_mask.shift_in (1);
+}
+
+/*
+ * we shift in from the top of the register towards the bottom
+ *
+ * +-- bits enter here...
+ * |
+ * v
+ * block 0 | block 1 | block 2 ... | block N-1
+ *                                          |
+ *                                          +--> ... and drop out here
+ *
+ */
+inline void
+atsci_sliding_correlator::shift_reg::shift_in (int bit)
+{
+  for (int i = NSRBLOCKS - 1; i > 0; i--)
+    d[i] = ((d[i-1] & 0x1) << (srblock_bitsize - 1)) | (d[i] >> 1);
+
+  d[0] = (((srblock) bit) << (srblock_bitsize - 1)) | (d[0] >> 1);
+}
+
+int
+atsci_sliding_correlator::input_bit (int bit)
+{
+  input.shift_in (bit);
+
+  // can probably get a win by unrolling the loop, if we need to.
+  int  count = 0;
+  for (int i = 0; i < NSRBLOCKS; i++)
+    count += popcount32 ((input.d[i] ^ mask.d[i]) & and_mask.d[i]);
+
+  return count;
+}
+