fix: unbounded_percentage always rounded down

For example if lower / upper = 0.019 (1.9%), it would return 1% instead
of 2%

Fixes #2399

CHANGELOG.md

@@ -109,6 +109,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([`#2292`](https://github.com/polybar/polybar/issues/2292))
 - Parser error if click command contained `}`
   ([`#2040`](https://github.com/polybar/polybar/issues/2040))
+- Slight imprecision when calculating percentages. This caused the volume
+  reported by alsa to be off by one.
+  ([`#2399`](https://github.com/polybar/polybar/issues/2399))
 - `internal/backlight`: With amdgpu backlights, the brightness indicator was slightly behind.
   ([`#2367](https://github.com/polybar/polybar/issues/2367))
 

include/utils/math.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <algorithm>
+#include <cmath>
 
 #include "common.hpp"
 
@@ -37,15 +38,17 @@ namespace math_util {
    * Calculate the percentage for a value
    * between min_value and max_value
    */
-  template<typename ValueType, typename ReturnType = int>
-  ReturnType unbounded_percentage(ValueType value, ValueType min_value, ValueType max_value){
+  template <typename ValueType, typename ReturnType = int>
+  ReturnType unbounded_percentage(ValueType value, ValueType min_value, ValueType max_value) {
     auto upper = (max_value - min_value);
     auto lower = static_cast<float>(value - min_value);
-    ValueType percentage = (lower / upper) * 100.0f;
-    if (std::is_integral<ReturnType>())
-      percentage += 0.5f;
+    float percentage = (lower / upper) * 100.0f;
+    if (std::is_integral<ReturnType>()) {
+      return static_cast<ReturnType>(std::round(percentage));
+    } else {
       return percentage;
     }
+  }
 
   /**
    * Calculates percentage for a value and
@@ -113,6 +116,6 @@ namespace math_util {
   inline int ceil(double value, int step = 1) {
     return static_cast<int>((value * 10 + step * 10 - 1) / (step * 10)) * step;
   }
-}
+}  // namespace math_util
 
 POLYBAR_NS_END

tests/unit_tests/utils/math.cpp

@@ -1,6 +1,7 @@
-#include "common/test.hpp"
 #include "utils/math.hpp"
 
+#include "common/test.hpp"
+
 using namespace polybar;
 
 TEST(Math, min) {
@@ -38,7 +39,7 @@ TEST(Math, percentage) {
   EXPECT_EQ(55.0f, (math_util::percentage<float, float>(5.5f, 0.0f, 10.0f)));
   EXPECT_EQ(56, (math_util::percentage<float, int>(5.55f, 0.0f, 10.0f)));
   EXPECT_EQ(43.75f, (math_util::percentage<float, float>(5.25f, 0.0f, 12.0f)));
-  EXPECT_EQ(41, (math_util::percentage<int, int>(5, 0, 12)));
+  EXPECT_EQ(42, (math_util::percentage<int, int>(5, 0, 12)));
   EXPECT_EQ(20.5f, (math_util::percentage<float, float>(20.5f, 0.0f, 100.0f)));
   EXPECT_EQ(70.0f, (math_util::percentage<float, float>(4.5f, 1.0f, 6.0f)));
   EXPECT_EQ(21, (math_util::percentage<float, int>(20.5f, 0.0f, 100.0f)));