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+# 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 HalveStrategy class."""
+
+
+from dataclasses import dataclass
+from typing import Optional, Tuple
+
+from ..discrete_interval import DiscreteInterval
+from ..discrete_load import DiscreteLoad
+from ..discrete_width import DiscreteWidth
+from ..relevant_bounds import RelevantBounds
+from .base import StrategyBase
+
+
+@dataclass
+class HalveStrategy(StrategyBase):
+ """First strategy to apply for a new current target.
+
+ Pick a load between initial lower bound and initial upper bound,
+ nominate it if it is (still) worth it.
+
+ In a sense, this can be viewed as an extension of preceding target's
+ bisect strategy. But as the current target may require a different
+ trial duration, it is better to do it for the new target.
+
+ Alternatively, this is a way to save one application
+ of subsequent refine strategy, thus avoiding reducing risk of triggering
+ an external search (slight time saver for highly unstable SUTs).
+ Either way, minor time save is achieved by preceding target
+ only needing to reach double of current target width.
+
+ If the distance between initial bounds is already at or below
+ current target width, the middle point is not nominated.
+ The reasoning is that in this case external search is likely
+ to get triggered by the subsequent refine strategies,
+ so attaining a relevant bound here is not as likely to help.
+ """
+
+ def nominate(
+ self, bounds: RelevantBounds
+ ) -> Tuple[Optional[DiscreteLoad], Optional[DiscreteWidth]]:
+ """Nominate the middle between initial lower and upper bound.
+
+ The returned width is the target width, even if initial bounds
+ happened to be closer together.
+
+ :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 not self.initial_lower_load or not self.initial_upper_load:
+ return None, None
+ interval = DiscreteInterval(
+ lower_bound=self.initial_lower_load,
+ upper_bound=self.initial_upper_load,
+ )
+ wig = interval.width_in_goals(self.target.discrete_width)
+ if wig > 2.0:
+ # Can happen for initial target.
+ return None, None
+ if wig <= 1.0:
+ # Already was narrow enough, refinements shall be sufficient.
+ return None, None
+ load = interval.middle(self.target.discrete_width)
+ if self.not_worth(bounds, load):
+ return None, None
+ self.debug(f"Halving available: {load}")
+ # TODO: Report possibly smaller width?
+ self.expander.limit(self.target.discrete_width)
+ return load, self.target.discrete_width