update miss penalty to use less flawed algo

src/osu_2019/pp.rs

@@ -357,7 +357,10 @@ impl<'m> OsuPP<'m> {
 
         // Penalize misses
         if effective_miss_count > 0.0 {
-            let miss_penalty = self.calculate_miss_penalty(effective_miss_count);
+            let miss_penalty = self.calculate_miss_penalty(
+                effective_miss_count,
+                attributes.aim_difficult_strain_count,
+            );
             aim_value *= miss_penalty;
         }
 
@@ -426,7 +429,10 @@ impl<'m> OsuPP<'m> {
 
         // Penalize misses
         if effective_miss_count > 0.0 {
-            let miss_penalty = self.calculate_miss_penalty(effective_miss_count);
+            let miss_penalty = self.calculate_miss_penalty(
+                effective_miss_count,
+                attributes.speed_difficult_strain_count,
+            );
             speed_value *= miss_penalty;
         }
 
@@ -504,11 +510,12 @@ impl<'m> OsuPP<'m> {
     }
 
     #[inline]
-    fn calculate_miss_penalty(&self, effective_miss_count: f32) -> f32 {
-        let total_hits = self.total_hits() as f32;
-
-        0.97 * (1.0 - (effective_miss_count / total_hits).powf(0.5))
-            .powf(1.0 + (effective_miss_count / 1.5))
+    fn calculate_miss_penalty(
+        &self,
+        effective_miss_count: f32,
+        difficult_strain_count: f32,
+    ) -> f32 {
+        0.94 / ((effective_miss_count / (2.0 * difficult_strain_count.sqrt())) + 1.0)
     }
 
     #[inline]

src/osu_2019/skill.rs

@@ -72,16 +72,13 @@ impl Skill {
         difficulty
     }
 
-    pub(crate) fn count_difficult_strains(&mut self) -> f64 {
-        let top_strain = self
-            .object_strains
-            .iter()
-            .fold(f64::NEG_INFINITY, |prev, curr| prev.max(*curr as f64));
+    pub(crate) fn count_difficult_strains(&mut self) -> f32 {
+        let single_strain = self.difficulty_value() / 10.0;
 
         self.object_strains
             .iter()
-            .map(|strain| (strain / top_strain as f32).powi(4))
-            .sum::<f32>() as f64
+            .map(|strain| 1.1 / (1.0 + (-10.0 * (strain / single_strain - 0.88)).exp()))
+            .sum::<f32>()
     }
 
     #[inline]

src/osu_2019/stars.rs

@@ -155,8 +155,8 @@ pub struct OsuDifficultyAttributes {
     pub n_spinners: usize,
     pub stars: f64,
     pub max_combo: usize,
-    pub aim_difficult_strain_count: f64,
-    pub speed_difficult_strain_count: f64,
+    pub aim_difficult_strain_count: f32,
+    pub speed_difficult_strain_count: f32,
 }
 
 #[derive(Clone, Debug)]