solver: select skyline candidate policy

Make candidate ordering an explicit deterministic policy and benchmark ascending, descending, and exact-width-first choices. Keep ascending as the default because it produces the best measured time to first solution despite best-fit's slightly smaller tree.

Retain the benchmark v1 interface and document why randomized and duplicate-work portfolio policies are deferred.

Tests: Release and Debug CTest (10 passed each)

Refs: #12

benchmarks/benchmark.cc

@@ -27,7 +27,7 @@ namespace {
   };
 
   auto solve(std::uint64_t order, bool instrument,
-             CandidateOrder candidate_order, bool direct_search,
+             SearchPolicy policy, bool direct_search,
              SearchCounters &counters)
       -> TimedSolution {
     auto const predecessor_order =
@@ -36,8 +36,8 @@ namespace {
     auto predecessor =
         instrument
             ? search_solution_instrumented(predecessor_order, counters,
-                                           candidate_order)
-            : search_solution(predecessor_order, candidate_order);
+                                           policy)
+            : search_solution(predecessor_order, policy);
     auto const search_end = Clock::now();
 
     auto const construction_begin = Clock::now();
@@ -95,7 +95,7 @@ namespace {
 int main(int argc, char **argv) {
   if (argc < 3 || argc > 5) {
     std::cerr << "usage: partridge_benchmark ORDER counters|plain "
-                 "[ascending|descending] [public|direct]\n";
+                 "[ascending|descending|best-fit] [public|direct]\n";
     return 2;
   }
   auto const order = static_cast<std::uint64_t>(std::strtoull(argv[1], nullptr, 10));
@@ -104,13 +104,16 @@ int main(int argc, char **argv) {
     std::cerr << "counter mode must be counters or plain\n";
     return 2;
   }
-  auto const candidate_order =
+  auto const policy =
       argc < 4 || std::string_view(argv[3]) == "ascending"
-          ? CandidateOrder::ascending
-          : CandidateOrder::descending;
+          ? SearchPolicy::ascending
+          : std::string_view(argv[3]) == "descending"
+                ? SearchPolicy::descending
+                : SearchPolicy::best_fit;
   if (argc >= 4 && std::string_view(argv[3]) != "ascending" &&
-      std::string_view(argv[3]) != "descending") {
-    std::cerr << "candidate order must be ascending or descending\n";
+      std::string_view(argv[3]) != "descending" &&
+      std::string_view(argv[3]) != "best-fit") {
+    std::cerr << "search policy must be ascending, descending, or best-fit\n";
     return 2;
   }
   auto const direct_search =
@@ -122,8 +125,7 @@ int main(int argc, char **argv) {
   }
 
   SearchCounters counters;
-  auto timed =
-      solve(order, instrument, candidate_order, direct_search, counters);
+  auto timed = solve(order, instrument, policy, direct_search, counters);
 
   auto const validation_begin = Clock::now();
   auto const validation_ok = valid(order, timed.result);
@@ -142,8 +144,9 @@ int main(int argc, char **argv) {
       << ",\"order\":" << order
       << ",\"instrumented\":" << boolean(instrument)
       << ",\"candidate_order\":\""
-      << (candidate_order == CandidateOrder::ascending ? "ascending"
-                                                       : "descending")
+      << (policy == SearchPolicy::ascending
+              ? "ascending"
+              : policy == SearchPolicy::descending ? "descending" : "best-fit")
       << "\""
       << ",\"search_route\":\""
       << (direct_search ? "direct" : "public") << "\""

benchmarks/run.py

@@ -79,11 +79,11 @@ def environment(binary):
     }
 
 
-def run_once(binary, order, mode, candidate_order, search_route, timeout):
+def run_once(binary, order, mode, search_policy, search_route, timeout):
     started = time.monotonic()
     try:
         process = subprocess.run(
-            [str(binary), str(order), mode, candidate_order, search_route],
+            [str(binary), str(order), mode, search_policy, search_route],
             check=False,
             capture_output=True,
             text=True,
@@ -218,7 +218,8 @@ def main():
     parser.add_argument("--timeout", type=float, default=600.0)
     parser.add_argument(
         "--candidate-order",
-        choices=("ascending", "descending"),
+        dest="search_policy",
+        choices=("ascending", "descending", "best-fit"),
         default="ascending",
     )
     parser.add_argument("--direct-search", action="store_true")
@@ -251,7 +252,7 @@ def main():
                     args.binary,
                     order,
                     mode,
-                    args.candidate_order,
+                    args.search_policy,
                     "direct" if args.direct_search else "public",
                     args.timeout,
                 )
@@ -262,7 +263,7 @@ def main():
                         args.binary,
                         order,
                         mode,
-                        args.candidate_order,
+                        args.search_policy,
                         "direct" if args.direct_search else "public",
                         args.timeout,
                     )
@@ -290,7 +291,7 @@ def main():
             "warmup_runs": args.warmup,
             "measured_repetitions": args.repetitions,
             "per_run_timeout_seconds": args.timeout,
-            "candidate_order": args.candidate_order,
+            "candidate_order": args.search_policy,
             "search_route": "direct" if args.direct_search else "public",
             "stdout": "captured; rendered grid suppressed by probe",
         },