From f72b65b2a54be664f4ce95e0a8bdc68d09562bf1 Mon Sep 17 00:00:00 2001
From: Claire Wolf <claire@symbioticeda.com>
Date: Tue, 17 Mar 2020 14:15:08 +0100
Subject: Using LFSR counter for ezSAT::manyhot()

The only user of this API right now is the puzzle3d benchmark and
it sees a slight reduction in CNF size from this, but the performance
difference is within the noise of measurement on my system.

Signed-off-by: Claire Wolf <claire@symbioticeda.com>
---
 libs/ezsat/ezsat.cc | 118 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)

diff --git a/libs/ezsat/ezsat.cc b/libs/ezsat/ezsat.cc
index 177bcd8a3..47fdb8efe 100644
--- a/libs/ezsat/ezsat.cc
+++ b/libs/ezsat/ezsat.cc
@@ -1389,6 +1389,7 @@ int ezSAT::onehot(const std::vector<int> &vec, bool max_only)
 	return expression(OpAnd, formula);
 }
 
+#if 0
 int ezSAT::manyhot(const std::vector<int> &vec, int min_hot, int max_hot)
 {
 	// many-hot encoding using a simple sorting network
@@ -1426,6 +1427,123 @@ int ezSAT::manyhot(const std::vector<int> &vec, int min_hot, int max_hot)
 
 	return expression(OpAnd, formula);
 }
+#else
+static std::vector<int> lfsr_sym(ezSAT *that, const std::vector<int> &vec, int poly)
+{
+	std::vector<int> out;
+
+	for (int i = 0; i < int(vec.size()); i++)
+		if ((poly & (1 << (i+1))) != 0) {
+			if (out.empty())
+				out.push_back(vec.at(i));
+			else
+				out.at(0) = that->XOR(out.at(0), vec.at(i));
+		}
+
+	for (int i = 0; i+1 < int(vec.size()); i++)
+		out.push_back(vec.at(i));
+
+	return out;
+}
+
+static int lfsr_num(int vec, int poly, int cnt = 1)
+{
+	int mask = poly >> 1;
+	mask |= mask >> 1;
+	mask |= mask >> 2;
+	mask |= mask >> 4;
+	mask |= mask >> 8;
+	mask |= mask >> 16;
+
+	while (cnt-- > 0) {
+		int bits = vec & (poly >> 1);
+		bits = ((bits & 0xAAAAAAAA) >>  1) ^ (bits & 0x55555555);
+		bits = ((bits & 0x44444444) >>  2) ^ (bits & 0x11111111);
+		bits = ((bits & 0x10101010) >>  4) ^ (bits & 0x01010101);
+		bits = ((bits & 0x01000100) >>  8) ^ (bits & 0x00010001);
+		bits = ((bits & 0x00010000) >> 16) ^ (bits & 0x00000001);
+		vec = ((vec << 1) | bits) & mask;
+	}
+
+	return vec;
+}
+
+int ezSAT::manyhot(const std::vector<int> &vec, int min_hot, int max_hot)
+{
+	// many-hot encoding using LFSR as counter
+
+	int poly = 0;
+	int nbits = 0;
+
+	if (vec.size() < 3) {
+		poly = (1 << 2) | (1 << 1) | 1;
+		nbits = 2;
+	} else
+	if (vec.size() < 7) {
+		poly = (1 << 3) | (1 << 2) | 1;
+		nbits = 3;
+	} else
+	if (vec.size() < 15) {
+		poly = (1 << 4) | (1 << 3) | 1;
+		nbits = 4;
+	} else
+	if (vec.size() < 31) {
+		poly = (1 << 5) | (1 << 3) | 1;
+		nbits = 5;
+	} else
+	if (vec.size() < 63) {
+		poly = (1 << 6) | (1 << 5) | 1;
+		nbits = 6;
+	} else
+	if (vec.size() < 127) {
+		poly = (1 << 7) | (1 << 6) | 1;
+		nbits = 7;
+	} else
+	// if (vec.size() < 255) {
+	//	poly = (1 << 8) | (1 << 6) | (1 << 5) | (1 << 4) | 1;
+	//	nbits = 8;
+	// } else
+	if (vec.size() < 511) {
+		poly = (1 << 9) | (1 << 5) | 1;
+		nbits = 9;
+	} else {
+		assert(0);
+	}
+
+	std::vector<int> min_val;
+	std::vector<int> max_val;
+
+	if (min_hot > 1)
+		min_val = vec_const_unsigned(lfsr_num(1, poly, min_hot), nbits);
+
+	if (max_hot >= 0)
+		max_val = vec_const_unsigned(lfsr_num(1, poly, max_hot+1), nbits);
+
+	std::vector<int> state = vec_const_unsigned(1, nbits);
+
+	std::vector<int> match_min;
+	std::vector<int> match_max;
+
+	if (min_hot == 1)
+		match_min = vec;
+
+	for (int i = 0; i < int(vec.size()); i++)
+	{
+		state = vec_ite(vec[i], lfsr_sym(this, state, poly), state);
+
+		if (!min_val.empty() && i+1 >= min_hot)
+			match_min.push_back(vec_eq(min_val, state));
+
+		if (!max_val.empty() && i >= max_hot)
+			match_max.push_back(vec_eq(max_val, state));
+	}
+
+	int min_matched = min_hot ? vec_reduce_or(match_min) : CONST_TRUE;
+	int max_matched = vec_reduce_or(match_max);
+
+	return AND(min_matched, NOT(max_matched));
+}
+#endif
 
 int ezSAT::ordered(const std::vector<int> &vec1, const std::vector<int> &vec2, bool allow_equal)
 {
-- 
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