X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=blobdiff_plain;f=src%2Fcore%2Fao_viterbi.c;h=bb93bc83b798540782e928a8c5ac4e0bf448c0fb;hp=17464cd1df3fd94cbf3a80638e2d17890a9cd901;hb=b292c14790fc225029cba3f80ce8ad6c5652bc4e;hpb=74f6a1a8c8fa9d5bb8d74c99782310b431dd4727

diff --git a/src/core/ao_viterbi.c b/src/core/ao_viterbi.c
index 17464cd1..bb93bc83 100644
--- a/src/core/ao_viterbi.c
+++ b/src/core/ao_viterbi.c
@@ -18,6 +18,35 @@
 #include <ao_fec.h>
 #include <stdio.h>
 
+/* 
+ * byte order repeats through 3 2 1 0
+ * 	
+ * bit-pair order repeats through
+ *
+ *  1/0 3/2 5/4 7/6
+ *
+ * So, the over all order is:
+ *
+ *	3,1/0 	2,1/0	1,1/0	0,1/0
+ *	3,3/2 	2,3/2	1,3/2	0,3/2
+ *	3,5/4	2,5/4	1,5/4	0,5/4
+ *	3,7/6	2,7/6	1,7/6	0,7/6
+ *
+ * The raw bit order is thus
+ *
+ *	1e/1f   16/17   0e/0f   06/07
+ *	1c/1d	14/15	0c/0d	04/05
+ *	1a/1b	12/13	0a/0b	02/03
+ *	18/19	10/11	08/09	00/01
+ */
+
+static inline uint16_t ao_interleave_index(uint16_t i) {
+	uint8_t		l = i & 0x1e;
+	uint16_t	h = i & ~0x1e;
+	uint8_t		o = 0x1e ^ (((l >> 2) & 0x6) | ((l << 2) & 0x18));
+	return h | o;
+}
+
 struct ao_soft_sym {
 	uint8_t	a, b;
 };
@@ -70,6 +99,9 @@ ao_fec_decode(uint8_t *in, uint16_t len, uint8_t *out)
 	uint8_t		n;				/* next cost/bits index */
 	uint8_t		state;				/* state index */
 	uint8_t		bit;				/* original encoded bit index */
+	const uint8_t	*whiten = ao_fec_whiten_table;
+	uint16_t	interleave;			/* input byte array index */
+	struct ao_soft_sym	s;			/* input symbol pair */
 
 	p = 0;
 	for (state = 0; state < NUM_STATE; state++) {
@@ -82,7 +114,13 @@ ao_fec_decode(uint8_t *in, uint16_t len, uint8_t *out)
 	for (i = 0; i < len; i += 2) {
 		b = i/2;
 		n = p ^ 1;
-		struct ao_soft_sym s = { .a = in[i], .b = in[i+1] };
+
+		/* Fetch one pair of input bytes, de-interleaving
+		 * the input.
+		 */
+		interleave = ao_interleave_index(i);
+		s.a = in[interleave];
+		s.b = in[interleave+1];
 
 		/* Reset next costs to 'impossibly high' values so that
 		 * the first path through this state is cheaper than this
@@ -159,10 +197,10 @@ ao_fec_decode(uint8_t *in, uint16_t len, uint8_t *out)
 			}
 
 #if 0
-			printf ("\tbit %3d min_cost %5d old bit %3d old_state %x bits %02x\n",
-				i/2, min_cost, o + 8, min_state, (bits[p][min_state] >> dist) & 0xff);
+			printf ("\tbit %3d min_cost %5d old bit %3d old_state %x bits %02x whiten %0x\n",
+				i/2, min_cost, o + 8, min_state, (bits[p][min_state] >> dist) & 0xff, *whiten);
 #endif
-			out[o >> 3] = bits[p][min_state] >> dist;
+			*out++ = (bits[p][min_state] >> dist) ^ *whiten++;
 			o += 8;
 		}
 	}