From f10202d9addddca60505019d32abefbec22359b7 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Fri, 27 Mar 2026 13:32:20 -1000
Subject: [PATCH] [sensor] Use std::array in CalibrateLinearFilter

---
 esphome/components/sensor/__init__.py |  4 +++-
 esphome/components/sensor/filter.cpp  | 11 ++++-------
 esphome/components/sensor/filter.h    | 22 ++++++++++++++++++----
 3 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/esphome/components/sensor/__init__.py b/esphome/components/sensor/__init__.py
index 9f3c1484b0..f7b6b963ba 100644
--- a/esphome/components/sensor/__init__.py
+++ b/esphome/components/sensor/__init__.py
@@ -784,7 +784,9 @@ async def calibrate_linear_filter_to_code(config, filter_id):
         linear_functions = [[k, b, float("NaN")]]
     elif config[CONF_METHOD] == "exact":
         linear_functions = map_linear(x, y)
-    return cg.new_Pvariable(filter_id, linear_functions)
+    return cg.new_Pvariable(
+        filter_id, cg.TemplateArguments(len(linear_functions)), linear_functions
+    )
 
 
 CONF_DEGREE = "degree"
diff --git a/esphome/components/sensor/filter.cpp b/esphome/components/sensor/filter.cpp
index d995ee4111..56f8879628 100644
--- a/esphome/components/sensor/filter.cpp
+++ b/esphome/components/sensor/filter.cpp
@@ -413,13 +413,10 @@ void HeartbeatFilter::setup() {
 
 float HeartbeatFilter::get_setup_priority() const { return setup_priority::HARDWARE; }
 
-CalibrateLinearFilter::CalibrateLinearFilter(std::initializer_list<std::array<float, 3>> linear_functions)
-    : linear_functions_(linear_functions) {}
-
-optional<float> CalibrateLinearFilter::new_value(float value) {
-  for (const auto &f : this->linear_functions_) {
-    if (!std::isfinite(f[2]) || value < f[2])
-      return (value * f[0]) + f[1];
+optional<float> calibrate_linear_compute(const std::array<float, 3> *functions, size_t count, float value) {
+  for (size_t i = 0; i < count; i++) {
+    if (!std::isfinite(functions[i][2]) || value < functions[i][2])
+      return (value * functions[i][0]) + functions[i][1];
   }
   return NAN;
 }
diff --git a/esphome/components/sensor/filter.h b/esphome/components/sensor/filter.h
index 6a76bd373e..606c820f26 100644
--- a/esphome/components/sensor/filter.h
+++ b/esphome/components/sensor/filter.h
@@ -3,6 +3,7 @@
 #include "esphome/core/defines.h"
 #ifdef USE_SENSOR_FILTER
 
+#include <array>
 #include <utility>
 #include <vector>
 #include "esphome/core/automation.h"
@@ -489,13 +490,26 @@ class OrFilter : public Filter {
   bool has_value_{false};
 };
 
-class CalibrateLinearFilter : public Filter {
+/// Non-template helper for linear calibration (implementation in filter.cpp)
+optional<float> calibrate_linear_compute(const std::array<float, 3> *functions, size_t count, float value);
+
+/// N is set by code generation to match the exact number of calibration segments.
+template<size_t N> class CalibrateLinearFilter : public Filter {
  public:
-  explicit CalibrateLinearFilter(std::initializer_list<std::array<float, 3>> linear_functions);
-  optional<float> new_value(float value) override;
+  explicit CalibrateLinearFilter(std::initializer_list<std::array<float, 3>> linear_functions) {
+    size_t i = 0;
+    for (const auto &f : linear_functions) {
+      if (i >= N)
+        break;
+      this->linear_functions_[i++] = f;
+    }
+  }
+  optional<float> new_value(float value) override {
+    return calibrate_linear_compute(this->linear_functions_.data(), N, value);
+  }
 
  protected:
-  FixedVector<std::array<float, 3>> linear_functions_;
+  std::array<std::array<float, 3>, N> linear_functions_{};
 };
 
 class CalibratePolynomialFilter : public Filter {