From 869678953dfbe22f2b784e8ec927bfa394676671 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 23 Feb 2026 17:03:24 -0600
Subject: [PATCH] [core] Add pow10_int helper, replace powf in
 normalize_accuracy and sensor filters (#14114)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
---
 esphome/components/sensor/filter.cpp |  5 +++--
 esphome/core/helpers.cpp             | 11 +++++++++--
 esphome/core/helpers.h               | 15 +++++++++++++++
 3 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/esphome/components/sensor/filter.cpp b/esphome/components/sensor/filter.cpp
index cd4db98457..0fe1effe17 100644
--- a/esphome/components/sensor/filter.cpp
+++ b/esphome/components/sensor/filter.cpp
@@ -5,6 +5,7 @@
 #include <cmath>
 #include "esphome/core/application.h"
 #include "esphome/core/hal.h"
+#include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 #include "sensor.h"
 
@@ -240,7 +241,7 @@ ValueListFilter::ValueListFilter(std::initializer_list<TemplatableValue<float>>
 
 bool ValueListFilter::value_matches_any_(float sensor_value) {
   int8_t accuracy = this->parent_->get_accuracy_decimals();
-  float accuracy_mult = powf(10.0f, accuracy);
+  float accuracy_mult = pow10_int(accuracy);
   float rounded_sensor = roundf(accuracy_mult * sensor_value);
 
   for (auto &filter_value : this->values_) {
@@ -472,7 +473,7 @@ optional<float> ClampFilter::new_value(float value) {
 RoundFilter::RoundFilter(uint8_t precision) : precision_(precision) {}
 optional<float> RoundFilter::new_value(float value) {
   if (std::isfinite(value)) {
-    float accuracy_mult = powf(10.0f, this->precision_);
+    float accuracy_mult = pow10_int(this->precision_);
     return roundf(accuracy_mult * value) / accuracy_mult;
   }
   return value;
diff --git a/esphome/core/helpers.cpp b/esphome/core/helpers.cpp
index 9f850b5df8..6d801e7ebc 100644
--- a/esphome/core/helpers.cpp
+++ b/esphome/core/helpers.cpp
@@ -468,8 +468,15 @@ ParseOnOffState parse_on_off(const char *str, const char *on, const char *off) {
 
 static inline void normalize_accuracy_decimals(float &value, int8_t &accuracy_decimals) {
   if (accuracy_decimals < 0) {
-    auto multiplier = powf(10.0f, accuracy_decimals);
-    value = roundf(value * multiplier) / multiplier;
+    float divisor;
+    if (accuracy_decimals == -1) {
+      divisor = 10.0f;
+    } else if (accuracy_decimals == -2) {
+      divisor = 100.0f;
+    } else {
+      divisor = pow10_int(-accuracy_decimals);
+    }
+    value = roundf(value / divisor) * divisor;
     accuracy_decimals = 0;
   }
 }
diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index 298b93fbc4..b606e68df3 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -439,6 +439,21 @@ template<size_t STACK_SIZE, typename T = uint8_t> class SmallBufferWithHeapFallb
 /// @name Mathematics
 ///@{
 
+/// Compute 10^exp using iterative multiplication/division.
+/// Avoids pulling in powf/__ieee754_powf (~2.3KB flash) for small integer exponents.
+/// Matches powf(10, exp) for the int8_t exponent range used by sensor accuracy_decimals.
+inline float pow10_int(int8_t exp) {
+  float result = 1.0f;
+  if (exp >= 0) {
+    for (int8_t i = 0; i < exp; i++)
+      result *= 10.0f;
+  } else {
+    for (int8_t i = exp; i < 0; i++)
+      result /= 10.0f;
+  }
+  return result;
+}
+
 /// Remap \p value from the range (\p min, \p max) to (\p min_out, \p max_out).
 template<typename T, typename U> T remap(U value, U min, U max, T min_out, T max_out) {
   return (value - min) * (max_out - min_out) / (max - min) + min_out;