1 files changed, 105 insertions, 0 deletions
diff --git a/gr-vocoder/lib/codec2/pack.c b/gr-vocoder/lib/codec2/pack.c
new file mode 100644
index 000000000..31551dfc4
--- /dev/null
+++ b/gr-vocoder/lib/codec2/pack.c
@@ -0,0 +1,105 @@
+/*
+  Copyright (C) 2010 Perens LLC <bruce@perens.com>
+
+  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 3 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, see <http://www.gnu.org/licenses/>.
+
+ */
+#include "defines.h"
+#include "quantise.h"
+#include <stdio.h>
+
+/* Compile-time constants */
+/* Size of unsigned char in bits. Assumes 8 bits-per-char. */
+static const unsigned int	WordSize = 8;
+
+/* Mask to pick the bit component out of bitIndex. */
+static const unsigned int	IndexMask = 0x7;
+
+/* Used to pick the word component out of bitIndex. */
+static const unsigned int	ShiftRight = 3;
+
+/** Pack a bit field into a bit string, encoding the field in Gray code.
+ *
+ * The output is an array of unsigned char data. The fields are efficiently
+ * packed into the bit string. The Gray coding is a naive attempt to reduce
+ * the effect of single-bit errors, we expect to do a better job as the
+ * codec develops.
+ *
+ * This code would be simpler if it just set one bit at a time in the string,
+ * but would hit the same cache line more often. I'm not sure the complexity
+ * gains us anything here.
+ *
+ * Although field is currently of int type rather than unsigned for
+ * compatibility with the rest of the code, indices are always expected to
+ * be >= 0.
+ */
+void
+pack(
+ unsigned char *	bitArray, /* The output bit string. */
+ unsigned int *		bitIndex, /* Index into the string in BITS, not bytes.*/
+ int			field,	  /* The bit field to be packed. */
+ unsigned int		fieldWidth/* Width of the field in BITS, not bytes. */
+ )
+{
+  /* Convert the field to Gray code */
+  field = (field >> 1) ^ field;
+
+  do {
+    unsigned int  	bI = *bitIndex;
+    unsigned int	bitsLeft = WordSize - (bI & IndexMask);
+    unsigned int	sliceWidth =
+			 bitsLeft < fieldWidth ? bitsLeft : fieldWidth;
+    unsigned int	wordIndex = bI >> ShiftRight;
+
+    bitArray[wordIndex] |=
+     ((unsigned char)((field >> (fieldWidth - sliceWidth))
+     << (bitsLeft - sliceWidth)));
+    
+    *bitIndex = bI + sliceWidth;
+    fieldWidth -= sliceWidth;
+  } while ( fieldWidth != 0 );
+}
+
+/** Unpack a field from a bit string, converting from Gray code to binary.
+ *
+ */
+int
+unpack(
+ const unsigned char *	bitArray, /* The input bit string. */
+ unsigned int *		bitIndex, /* Index into the string in BITS, not bytes.*/
+ unsigned int		fieldWidth/* Width of the field in BITS, not bytes. */
+ )
+{
+  unsigned int	field = 0;
+  unsigned int	t;
+
+  do {
+    unsigned int  	bI = *bitIndex;
+    unsigned int	bitsLeft = WordSize - (bI & IndexMask);
+    unsigned int	sliceWidth =
+			 bitsLeft < fieldWidth ? bitsLeft : fieldWidth;
+
+    field |= (((bitArray[bI >> ShiftRight] >> (bitsLeft - sliceWidth)) & ((1 << sliceWidth) - 1)) << (fieldWidth - sliceWidth));
+    
+    *bitIndex = bI + sliceWidth;
+    fieldWidth -= sliceWidth;
+  } while ( fieldWidth != 0 );
+
+  /* Convert from Gray code to binary. Works for maximum 8-bit fields. */
+  t = field ^ (field >> 8);
+  t ^= (t >> 4);
+  t ^= (t >> 2);
+  t ^= (t >> 1);
+  return t;
+}