[Commit-gnuradio] r9557 - gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general

[jcorgan]

Author: jcorgan
Date: 2008-09-11 19:09:42 -0600 (Thu, 11 Sep 2008)
New Revision: 9557

Modified:
   
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/gri_lfsr.h
   
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.cc
   
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.h
Log:
Added scrambler and descrambler operations to gri_lfsr

Modified: 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/gri_lfsr.h
===================================================================
--- 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/gri_lfsr.h
   2008-09-11 20:00:47 UTC (rev 9556)
+++ 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/gri_lfsr.h
   2008-09-12 01:09:42 UTC (rev 9557)
@@ -58,15 +58,29 @@
  *
  *
  *
- *  next_bit() - performs once cycle of the lfsr,
- *               generating the new high order bit from the mask
- *               and returning the low order bit which has been
- *               shifted out of the register.
+ *  next_bit() - Standard LFSR operation
+ * 
+ *      Perform one cycle of the LFSR.  The output bit is taken from
+ *      the shift register LSB.  The shift register MSB is assigned from
+ *      the modulo 2 sum of the masked shift register.
+ *             
+ *  next_bit_scramble(unsigned char input) - Scramble an input stream
+ * 
+ *      Perform one cycle of the LFSR.  The output bit is taken from
+ *      the shift register LSB.  The shift register MSB is assigned from
+ *      the modulo 2 sum of the masked shift register and the input LSB.
  *
+ *  next_bit_descramble(unsigned char input) - Descramble an input stream
  *
+ *      Perform one cycle of the LFSR.  The output bit is taken from 
+ *      the modulo-2 sum of the masked shift register and the input LSB.
+ *      The shift register MSB is assigned from the LSB of the input.
+ *
+ * See http://en.wikipedia.org/wiki/Scrambler for operation of these
+ * last two functions (see multiplicative scrambler.)
+ *
  */
 
-
 class gri_lfsr
 {
  private:
@@ -92,12 +106,29 @@
   }
 
   unsigned char next_bit() {
-    unsigned char bit = d_shift_register & 1;
+    unsigned char output = d_shift_register & 1;
     unsigned char newbit = popCount( d_shift_register & d_mask )%2;
     d_shift_register = ((d_shift_register>>1) | 
(newbit<<d_shift_register_length));
-    return bit;
+    return output;
   }
 
+  unsigned char next_bit_scramble(unsigned char input) {
+    unsigned char output = d_shift_register & 1;
+    unsigned char newbit = (popCount( d_shift_register & d_mask )%2)^(input & 
1);
+    //printf("reg=%08X in=%1d out=%1d new=%1d ", d_shift_register, input, 
output, newbit);
+    d_shift_register = ((d_shift_register>>1) | 
(newbit<<d_shift_register_length));
+    //printf("reg=%08X\n", d_shift_register);
+    return output;
+  }
+
+  unsigned char next_bit_descramble(unsigned char input) {
+    unsigned char output = (popCount( d_shift_register & d_mask )%2)^(input & 
1);
+    unsigned char newbit = input & 1;
+    d_shift_register = ((d_shift_register>>1) | 
(newbit<<d_shift_register_length));
+    return output;
+  }
+
+
   /*!
    * Rotate the register through x number of bits
    * where we are just throwing away the results to get queued up correctly

Modified: 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.cc
===================================================================
--- 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.cc
       2008-09-11 20:00:47 UTC (rev 9556)
+++ 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.cc
       2008-09-12 01:09:42 UTC (rev 9557)
@@ -54,3 +54,87 @@
   CPPUNIT_ASSERT_THROW(gri_lfsr(mask, seed, 32), std::invalid_argument);
 }
 
+void
+qa_gri_lfsr::test_scrambler()
+{
+  // CCSDS 7-bit scrambler
+  int mask = 0x8A; // 1+x^4+X^6 
+  int seed = 0x7F;
+  int length = 7;
+
+  gri_lfsr scrambler(mask, seed, length);
+
+  // Impulse (1 and 126 more zeroes)
+  unsigned char src[] = 
+    { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0 }; // flush bits
+  
+  // Impulse response (including leading bits)
+  unsigned char expected[] =
+    { 1, 1, 1, 1, 1, 1, 1, 
+      0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0, 
+      0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 
+      0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 
+      0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 
+      1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 
+      0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 
+      1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 
+      1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, };
+
+  int len = sizeof(src);
+  unsigned char actual[len];
+
+  for (int i = 0; i < len; i++)
+    actual[i] = scrambler.next_bit_scramble(src[i]);
+
+  CPPUNIT_ASSERT(memcmp(expected, actual, len) == 0);
+}
+
+void
+qa_gri_lfsr::test_descrambler()
+{
+  // CCSDS 7-bit scrambler
+  int mask = 0x8A; // 1+x^4+X^6 
+  int seed = 0x7F;
+  int length = 7;
+
+  gri_lfsr descrambler(mask, seed, length);
+
+  // Scrambled sequence (impulse response)
+  unsigned char src[] =
+    { 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0, 
+      0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 
+      0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 
+      0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 
+      1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 
+      0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 
+      1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 
+      1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0 }; 
+
+  // Original (garbage while synchronizing, them impulse)
+  unsigned char expected[] = 
+    { 0, 1, 0, 0, 1, 0,
+      1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+      0, 0, 0, 0, 0, 0, 0, 0, 0 };
+  
+  int len = sizeof(src);
+  unsigned char actual[len];
+
+  for (int i = 0; i < len; i++)
+    actual[i] = descrambler.next_bit_descramble(src[i]);
+
+  CPPUNIT_ASSERT(memcmp(expected, actual, len) == 0);
+}

Modified: 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.h
===================================================================
--- 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.h
        2008-09-11 20:00:47 UTC (rev 9556)
+++ 
gnuradio/branches/developers/jcorgan/scr/gnuradio-core/src/lib/general/qa_gri_lfsr.h
        2008-09-12 01:09:42 UTC (rev 9557)
@@ -29,10 +29,14 @@
 
   CPPUNIT_TEST_SUITE(qa_gri_lfsr);
   CPPUNIT_TEST(test_lfsr);
+  CPPUNIT_TEST(test_scrambler);
+  CPPUNIT_TEST(test_descrambler);
   CPPUNIT_TEST_SUITE_END();
 
  private:
   void test_lfsr();
+  void test_scrambler();
+  void test_descrambler();
 };
 
 #endif /* _QA_GRI_LFSR_H_ */