[core] Add step_to_accuracy_decimals benchmarks (#18826)

tests/benchmarks/core/bench_helpers.cpp

@@ -363,4 +363,47 @@ static void Snprintf_Uint32_Large(benchmark::State &state) {
 }
 BENCHMARK(Snprintf_Uint32_Large);
 
+// --- step_to_accuracy_decimals() ---
+// Called from climate traits and web_server for every number/climate step.
+
+static void StepToAccuracyDecimals_Tenth(benchmark::State &state) {
+  for (auto _ : state) {
+    int result = 0;
+    for (int i = 0; i < kInnerIterations; i++) {
+      result += step_to_accuracy_decimals(0.1f);
+    }
+    benchmark::DoNotOptimize(result);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(StepToAccuracyDecimals_Tenth);
+
+static void StepToAccuracyDecimals_Whole(benchmark::State &state) {
+  for (auto _ : state) {
+    int result = 0;
+    for (int i = 0; i < kInnerIterations; i++) {
+      result += step_to_accuracy_decimals(1.0f);
+    }
+    benchmark::DoNotOptimize(result);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(StepToAccuracyDecimals_Whole);
+
+static void StepToAccuracyDecimals_Mixed(benchmark::State &state) {
+  static constexpr float steps[] = {
+      0.001f, 0.01f, 0.05f, 0.1f, 0.25f, 0.5f, 1.0f, 2.5f, 5.0f, 10.0f,
+  };
+  static constexpr int num_steps = sizeof(steps) / sizeof(steps[0]);
+  for (auto _ : state) {
+    int result = 0;
+    for (int i = 0; i < kInnerIterations; i++) {
+      result += step_to_accuracy_decimals(steps[i % num_steps]);
+    }
+    benchmark::DoNotOptimize(result);
+  }
+  state.SetItemsProcessed(state.iterations() * kInnerIterations);
+}
+BENCHMARK(StepToAccuracyDecimals_Mixed);
+
 }  // namespace esphome::benchmarks

tests/components/core/test_helpers.cpp

@@ -1,4 +1,5 @@
 #include <gtest/gtest.h>
+#include <cmath>
 #include <cstring>
 
 #include "esphome/core/alloc_helpers.h"
@@ -280,4 +281,71 @@ TEST(Base64, Rfc4648Vectors) {
   }
 }
 
+// --- step_to_accuracy_decimals() ---
+
+TEST(StepToAccuracyDecimals, TypicalSteps) {
+  EXPECT_EQ(step_to_accuracy_decimals(0.001f), 3);
+  EXPECT_EQ(step_to_accuracy_decimals(0.005f), 3);
+  EXPECT_EQ(step_to_accuracy_decimals(0.01f), 2);
+  EXPECT_EQ(step_to_accuracy_decimals(0.025f), 3);
+  EXPECT_EQ(step_to_accuracy_decimals(0.05f), 2);
+  EXPECT_EQ(step_to_accuracy_decimals(0.1f), 1);
+  EXPECT_EQ(step_to_accuracy_decimals(0.25f), 2);
+  EXPECT_EQ(step_to_accuracy_decimals(0.5f), 1);
+  EXPECT_EQ(step_to_accuracy_decimals(1.5f), 1);
+  EXPECT_EQ(step_to_accuracy_decimals(2.5f), 1);
+}
+
+TEST(StepToAccuracyDecimals, WholeSteps) {
+  EXPECT_EQ(step_to_accuracy_decimals(1.0f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(2.0f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(5.0f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(10.0f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(100.0f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(1000.0f), 0);
+}
+
+TEST(StepToAccuracyDecimals, FiveSignificantDigits) {
+  EXPECT_EQ(step_to_accuracy_decimals(1.23456f), 4);
+  EXPECT_EQ(step_to_accuracy_decimals(12.345f), 3);
+  EXPECT_EQ(step_to_accuracy_decimals(123.45f), 2);
+  EXPECT_EQ(step_to_accuracy_decimals(1234.5f), 1);
+  EXPECT_EQ(step_to_accuracy_decimals(12345.0f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(0.33333f), 5);
+  EXPECT_EQ(step_to_accuracy_decimals(0.0001f), 4);
+}
+
+TEST(StepToAccuracyDecimals, TrailingZerosDropped) {
+  EXPECT_EQ(step_to_accuracy_decimals(0.3f), 1);
+  EXPECT_EQ(step_to_accuracy_decimals(0.7f), 1);
+  EXPECT_EQ(step_to_accuracy_decimals(0.125f), 3);
+  EXPECT_EQ(step_to_accuracy_decimals(0.0625f), 4);
+}
+
+TEST(StepToAccuracyDecimals, RoundsUpToWholeNumber) {
+  // Rounds to five significant digits first, so this becomes 10 with no decimals.
+  EXPECT_EQ(step_to_accuracy_decimals(9.999999f), 0);
+}
+
+TEST(StepToAccuracyDecimals, OutsideFixedNotationRange) {
+  // %.5g prints these in exponent form, so the count comes from parsing "1e-05" or "1.2346e+05".
+  EXPECT_EQ(step_to_accuracy_decimals(0.00001f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(0.000125f), 6);
+  EXPECT_EQ(step_to_accuracy_decimals(123456.0f), 8);
+  EXPECT_EQ(step_to_accuracy_decimals(1000000.0f), 0);
+}
+
+TEST(StepToAccuracyDecimals, SignIgnored) {
+  EXPECT_EQ(step_to_accuracy_decimals(-0.1f), 1);
+  EXPECT_EQ(step_to_accuracy_decimals(-0.25f), 2);
+  EXPECT_EQ(step_to_accuracy_decimals(-1.0f), 0);
+}
+
+TEST(StepToAccuracyDecimals, NonFiniteAndZero) {
+  EXPECT_EQ(step_to_accuracy_decimals(0.0f), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(NAN), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(INFINITY), 0);
+  EXPECT_EQ(step_to_accuracy_decimals(-INFINITY), 0);
+}
+
 }  // namespace esphome::core::testing