do multi-round using a smaller list size

pac_encoder.hh

@@ -22,7 +22,7 @@ class PACEncoder
 		bool b4 = (*state >> 4) & 1;
 		bool b6 = (*state >> 6) & 1;
 		bool output = input ^ b1 ^ b3 ^ b4 ^ b6;
-		*state = ((*state & 126) << 1) | (input ? 2 : 0) | (output ? 1 : 0);
+		*state = ((*state & 62) << 1) | (input ? 2 : 0) | (output ? 1 : 0);
 		return output;
 	}
 public:
@@ -31,11 +31,22 @@ public:
 		int length = 1 << level;
 		int state = 0;
 		int frozen = length - mesg_bits;
-		for (int i = 0; i < length; i += 2) {
-			TYPE msg0 = rank_map[i] < frozen ? PH::one() : *message++;
-			TYPE msg1 = rank_map[i+1] < frozen ? PH::one() : *message++;
-			msg0 = 1 - 2 * conv(&state, msg0 < 0);
-			msg1 = 1 - 2 * conv(&state, msg1 < 0);
+		for (int i = 0, j = 0; i < length; i += 2) {
+			TYPE msg0 = rank_map[i] < frozen ? PH::one() : message[j++];
+			if (j)
+				conv(&state, msg0 < 0);
+			TYPE msg1 = rank_map[i+1] < frozen ? PH::one() : message[j++];
+			if (j)
+				conv(&state, msg1 < 0);
+		}
+		state |= (state & 126) << 7;
+		for (int i = 0, j = 0; i < length; i += 2) {
+			TYPE msg0 = rank_map[i] < frozen ? PH::one() : message[j++];
+			if (j)
+				msg0 = 1 - 2 * conv(&state, msg0 < 0);
+			TYPE msg1 = rank_map[i+1] < frozen ? PH::one() : message[j++];
+			if (j)
+				msg1 = 1 - 2 * conv(&state, msg1 < 0);
 			codeword[i] = PH::qmul(msg0, msg1);
 			codeword[i+1] = msg1;
 		}

pac_list_decoder.hh

@@ -46,19 +46,23 @@ struct PACListTree<TYPE, 1>
 		bool b4 = (*state >> 4) & 1;
 		bool b6 = (*state >> 6) & 1;
 		bool output = input ^ b1 ^ b3 ^ b4 ^ b6;
-		*state = ((*state & 126) << 1) | (input ? 2 : 0) | (output ? 1 : 0);
+		*state = ((*state & 62) << 1) | (input ? 2 : 0) | (output ? 1 : 0);
 		return output;
 	}
-	static MAP rate0(PATH *metric, int *state, TYPE *hard, TYPE *soft)
+	static MAP rate0(PATH *metric, int *count, int *state, TYPE *hard, TYPE *soft)
 	{
 		TYPE sft = soft[1];
-		for (int k = 0; k < TYPE::SIZE; ++k)
-			if (conv(state+k, 0) != (sft.v[k] < 0))
-				metric[k] += std::abs(sft.v[k]);
-		TYPE hrd;
-		for (int k = 0; k < TYPE::SIZE; ++k)
-			hrd.v[k] = 1 - 2 * (state[k] & 1);
-		*hard = hrd;
+		if (*count) {
+			for (int k = 0; k < TYPE::SIZE; ++k)
+				if (conv(state+k, 0) != (sft.v[k] < 0))
+					metric[k] += std::abs(sft.v[k]);
+			TYPE hrd;
+			for (int k = 0; k < TYPE::SIZE; ++k)
+				hrd.v[k] = 1 - 2 * (state[k] & 1);
+			*hard = hrd;
+		} else {
+			*hard = PH::one();
+		}
 		MAP map;
 		for (int k = 0; k < TYPE::SIZE; ++k)
 			map.v[k] = k;
@@ -102,12 +106,12 @@ struct PACListTree<TYPE, 1>
 		soft[1] = PH::prod(soft[2], soft[3]);
 		MAP lmap, rmap;
 		if (rank[0] < frozen)
-			lmap = rate0(metric, state, hard, soft);
+			lmap = rate0(metric, count, state, hard, soft);
 		else
 			lmap = rate1(metric, message, maps, count, state, hard, soft);
 		soft[1] = PH::madd(hard[0], vshuf(soft[2], lmap), vshuf(soft[3], lmap));
 		if (rank[1] < frozen)
-			rmap = rate0(metric, state, hard+1, soft);
+			rmap = rate0(metric, count, state, hard+1, soft);
 		else
 			rmap = rate1(metric, message, maps, count, state, hard+1, soft);
 		hard[0] = PH::qmul(vshuf(hard[0], rmap), hard[1]);
@@ -132,17 +136,49 @@ public:
 	{
 		assert(level <= MAX_M);
 		PATH metric[TYPE::SIZE];
-		int count = 0;
+		int state[TYPE::SIZE];
+		int count;
+		int length = 1 << level;
+		int frozen = length - mesg_bits;
+		int best_metric = 1000000;
+		int best_round = 0;
+
+		for (int round = 0; round < 64; ++round) {
+			count = 0;
+			metric[0] = 0;
+			for (int k = 1; k < TYPE::SIZE; ++k)
+				metric[k] = 1000000;
+			for (int i = 0; i < length; ++i)
+				soft[length+i] = vdup<TYPE>(codeword[i]);
+			state[0] = round << 1;
+			for (int i = 1; i < TYPE::SIZE; ++i)
+				state[i] = 0;
+
+			switch (level) {
+			case 5: PACListTree<TYPE, 5>::decode(metric, message, maps, &count, state, hard, soft, rank_map, frozen); break;
+			case 6: PACListTree<TYPE, 6>::decode(metric, message, maps, &count, state, hard, soft, rank_map, frozen); break;
+			case 7: PACListTree<TYPE, 7>::decode(metric, message, maps, &count, state, hard, soft, rank_map, frozen); break;
+			case 8: PACListTree<TYPE, 8>::decode(metric, message, maps, &count, state, hard, soft, rank_map, frozen); break;
+			default: assert(false);
+			}
+
+			for (int i = 0; i < TYPE::SIZE; ++i) {
+				if (round == ((state[i] & 126) >> 1) && metric[i] < best_metric) {
+					best_metric = metric[i];
+					best_round = round;
+				}
+			}
+		}
+
+		count = 0;
 		metric[0] = 0;
 		for (int k = 1; k < TYPE::SIZE; ++k)
 			metric[k] = 1000000;
-		int length = 1 << level;
 		for (int i = 0; i < length; ++i)
 			soft[length+i] = vdup<TYPE>(codeword[i]);
-		int state[TYPE::SIZE];
-		for (int i = 0; i < TYPE::SIZE; ++i)
+		state[0] = best_round << 1;
+		for (int i = 1; i < TYPE::SIZE; ++i)
 			state[i] = 0;
-		int frozen = length - mesg_bits;
 
 		switch (level) {
 		case 5: PACListTree<TYPE, 5>::decode(metric, message, maps, &count, state, hard, soft, rank_map, frozen); break;
@@ -151,13 +187,21 @@ public:
 		case 8: PACListTree<TYPE, 8>::decode(metric, message, maps, &count, state, hard, soft, rank_map, frozen); break;
 		default: assert(false);
 		}
-
+		for (int i = 0; i < TYPE::SIZE; ++i)
+			if (best_round != ((state[i] & 126) >> 1))
+				metric[i] = 1000000;
+		int perm[TYPE::SIZE];
+		CODE::insertion_sort(perm, metric, TYPE::SIZE);
 		for (int i = 0, r = 0; rank != nullptr && i < TYPE::SIZE; ++i) {
 			if (i > 0 && metric[i-1] != metric[i])
 				++r;
 			rank[i] = r;
 		}
-		MAP acc = maps[count-1];
+		MAP acc;
+		for (int k = 0; k < TYPE::SIZE; ++k)
+			acc.v[k] = perm[k];
+		message[count-1] = vshuf(message[count-1], acc);
+		acc = vshuf(maps[count-1], acc);
 		for (int i = count-2; i >= 0; --i) {
 			message[i] = vshuf(message[i], acc);
 			acc = vshuf(maps[i], acc);

tests/pac_list_regression_test.cc

@@ -30,10 +30,10 @@ int main()
 	const int C = 16;
 	int K = R * N + crc_aided * C;
 #if 1
-	const int L = 64;
+	const int L = 16;
 	typedef int8_t code_type;
 #else
-	const int L = 16;
+	const int L = 4;
 	typedef float code_type;
 #endif