Replace Python numerical kernels with native C execution

app/simulation/sampling.py

@@ -0,0 +1,101 @@
+"""Validate the requested output time grid before starting the C worker."""
+from __future__ import annotations
+from math import floor, isfinite
+from sys import maxsize
+from app.simulation.config import SolveIVPConfig
+
+class SimulationSampleTimeError(ValueError):
+    """Stable failure contract for an unsafe or unrepresentable sample grid."""
+
+    def __init__(self, code: str, message: str) -> None:
+        super().__init__(message)
+        self.code = code
+
+def simulation_sample_times(
+    config: SolveIVPConfig,
+    step: float,
+) -> list[float]:
+    t_start = float(config.t_start)
+    t_stop = float(config.t_stop)
+    if not isfinite(t_start) or not isfinite(t_stop):
+        raise SimulationSampleTimeError(
+            "SIMULATION_VALUE_NOT_FINITE",
+            "Simulation start and stop times must be finite.",
+        )
+    if step <= 0.0 or not isfinite(step):
+        raise SimulationSampleTimeError(
+            "SIMULATION_SAMPLE_STEP_INVALID",
+            "Simulation sample step must be finite and greater than zero.",
+        )
+    duration = t_stop - t_start
+    if not isfinite(duration):
+        raise SimulationSampleTimeError(
+            "SIMULATION_TIME_SPAN_NOT_FINITE",
+            "Simulation time span must be finite.",
+        )
+    if duration <= 0.0:
+        raise SimulationSampleTimeError(
+            "SIMULATION_TIME_RANGE_INVALID",
+            "Simulation stop time must be greater than start time.",
+        )
+
+    ratio = duration / step
+    if not isfinite(ratio):
+        raise SimulationSampleTimeError(
+            "SIMULATION_SAMPLE_COUNT_UNREPRESENTABLE",
+            "Simulation sample count cannot be represented by this runtime; "
+            "increase sampleStep.",
+        )
+    interval_count = floor(ratio)
+    # There is no product-level point cap. Still reject a collection that the
+    # Python runtime cannot index before multiplying by the potentially huge
+    # interval count or allocating the output grid.
+    if interval_count > maxsize - 2:
+        raise SimulationSampleTimeError(
+            "SIMULATION_SAMPLE_COUNT_UNREPRESENTABLE",
+            "Simulation sample count cannot be represented by this runtime; "
+            "increase sampleStep.",
+        )
+    last_regular_time = t_start + interval_count * step
+    append_stop = last_regular_time < t_stop
+    requested_point_count = interval_count + 1 + int(append_stop)
+    if requested_point_count > maxsize:
+        raise SimulationSampleTimeError(
+            "SIMULATION_SAMPLE_COUNT_UNREPRESENTABLE",
+            "Simulation sample count cannot be represented by this runtime; "
+            "increase sampleStep.",
+        )
+
+    times = [t_start]
+    for index in range(1, interval_count + 1):
+        candidate = t_start + index * step
+        if not isfinite(candidate):
+            raise SimulationSampleTimeError(
+                "SIMULATION_SAMPLE_TIME_UNREPRESENTABLE",
+                "Simulation sampleStep cannot be represented over the requested "
+                "absolute time range.",
+            )
+        if candidate >= t_stop:
+            candidate = t_stop
+        if candidate <= times[-1]:
+            raise SimulationSampleTimeError(
+                "SIMULATION_SAMPLE_TIME_UNREPRESENTABLE",
+                "Simulation sampleStep is too small to advance floating-point "
+                "time over the requested absolute time range.",
+            )
+        times.append(candidate)
+        if candidate == t_stop:
+            break
+    if times[-1] < t_stop:
+        times.append(t_stop)
+
+    if len(times) < 2 or any(
+        current >= following
+        for current, following in zip(times, times[1:])
+    ):
+        raise SimulationSampleTimeError(
+            "SIMULATION_SAMPLE_TIME_UNREPRESENTABLE",
+            "Simulation sample times must contain at least two strictly "
+            "increasing values.",
+        )
+    return times