1 files changed, 76 insertions, 0 deletions
diff --git a/resources/libraries/python/MLRsearch/strategy/extend_lo.py b/resources/libraries/python/MLRsearch/strategy/extend_lo.py
new file mode 100644
index 0000000000..68d20b6a6a
--- /dev/null
+++ b/resources/libraries/python/MLRsearch/strategy/extend_lo.py
@@ -0,0 +1,76 @@
+# Copyright (c) 2023 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining ExtendLoStrategy class."""
+
+
+from dataclasses import dataclass
+from typing import Optional, Tuple
+
+from ..discrete_load import DiscreteLoad
+from ..discrete_width import DiscreteWidth
+from ..relevant_bounds import RelevantBounds
+from .base import StrategyBase
+
+
+@dataclass
+class ExtendLoStrategy(StrategyBase):
+    """This strategy is applied when there is no relevant lower bound.
+
+    Typically this is needed after RefineLoStrategy turned initial lower bound
+    into a current relevant upper bound.
+    """
+
+    def nominate(
+        self, bounds: RelevantBounds
+    ) -> Tuple[Optional[DiscreteLoad], Optional[DiscreteWidth]]:
+        """Nominate current relevant upper bound minus expander width.
+
+        This performs external search in downwards direction,
+        until a valid lower bound for the current target is found,
+        or until min load is hit.
+        Limit handling is used to avoid nominating too close
+        (or below) the min rate.
+
+        Width expansion is only applied if the candidate becomes an upper bound,
+        so that is detected in done method.
+
+        :param bounds: Freshly updated bounds relevant for current target.
+        :type bounds: RelevantBounds
+        :returns: Two nones or candidate intended load and duration.
+        :rtype: Tuple[Optional[DiscreteLoad], Optional[DiscreteWidth]]
+        """
+        if bounds.clo or not bounds.chi or bounds.chi <= self.handler.min_load:
+            return None, None
+        width = self.expander.get_width()
+        load = self.handler.handle(
+            load=bounds.chi - width,
+            width=self.target.discrete_width,
+            clo=bounds.clo,
+            chi=bounds.chi,
+        )
+        if self.not_worth(bounds=bounds, load=load):
+            return None, None
+        self.debug(f"No clo, extending down: {load}")
+        return load, width
+
+    def won(self, bounds: RelevantBounds, load: DiscreteLoad) -> None:
+        """Expand width if the load became new upper bound.
+
+        :param bounds: Freshly updated bounds relevant for current target.
+        :param load: The current load, so strategy does not need to remember.
+        :type bounds: RelevantBounds
+        :type load: DiscreteLoad
+        """
+        if load == bounds.chi:
+            self.expander.expand()