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+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2021  Symbiflow Authors
+ *
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+#ifndef LOOKAHEAD_H
+#define LOOKAHEAD_H
+
+#include <algorithm>
+#include <vector>
+
+#include "cost_map.h"
+#include "deterministic_rng.h"
+#include "hash_table.h"
+#include "lookahead.capnp.h"
+#include "nextpnr_namespaces.h"
+#include "type_wire.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+// Lookahead is a routing graph generic lookahead builder and evaluator.
+//
+// The lookahead data model is structured into 3 parts:
+//  - Output site wires to routing network cost
+//  - Routing network point to point cost
+//  - Routing network cost to input site wires
+//
+//  If the lookahead is invoked from a routing wire to a routing wire, only
+//  the point to point cost is used.
+//
+//  If the lookahead is invoked from an output site wire to a routing wire,
+//  the point to point cost is computed using the cheapest output routing wire
+//  from the current site wire and then returned cost is the sum of the output
+//  cost plus the point to point routing network cost.
+//
+//  If the lookahead is invoked from a routing wire to an input site wire,
+//  then the cost is the point to point routing cost to the cheapest input
+//  routing wire plus the input routing cost.
+//
+//  If the lookahead is invoked from an output site wire to an input site wire,
+//  then cost is the sum of each of the 3 parts.
+struct Lookahead
+{
+    void init(const Context *, DeterministicRNG *rng);
+    void build_lookahead(const Context *, DeterministicRNG *rng);
+
+    bool read_lookahead(const std::string &chipdb_hash, const std::string &file);
+    void write_lookahead(const std::string &chipdb_hash, const std::string &file) const;
+    bool from_reader(const std::string &chipdb_hash, lookahead_storage::Lookahead::Reader reader);
+    void to_builder(const std::string &chipdb_hash, lookahead_storage::Lookahead::Builder builder) const;
+
+    delay_t estimateDelay(const Context *, WireId src, WireId dst) const;
+
+    struct InputSiteWireCost
+    {
+        // This wire is the cheapest non-site wire that leads to this site
+        // wire.
+        TypeWireId route_to;
+
+        // This is the cost from the cheapest_route_to wire to the site wire in
+        // question.
+        delay_t cost;
+    };
+
+    struct OutputSiteWireCost
+    {
+        // This wire is the cheapest non-site wire that is reachable from
+        // this site wire.
+        TypeWireId cheapest_route_from;
+
+        // This is the cost from the site wire in question to
+        // cheapest_route_from wire.
+        delay_t cost;
+    };
+
+    HashTables::HashMap<TypeWireId, std::vector<InputSiteWireCost>> input_site_wires;
+    HashTables::HashMap<TypeWireId, OutputSiteWireCost> output_site_wires;
+    HashTables::HashMap<TypeWirePair, delay_t> site_to_site_cost;
+    CostMap cost_map;
+};
+
+NEXTPNR_NAMESPACE_END
+
+#endif /* LOOKAHEAD_H */