Improve the QueryEnhancer by doing a single lookup

meilisearch-core/src/automaton/query_enhancer.rs

@@ -147,35 +147,37 @@ impl<S: AsRef<str>> QueryEnhancerBuilder<'_, S> {
     }
 
     pub fn build(self) -> QueryEnhancer {
-        QueryEnhancer {
-            origins: self.origins,
-            real_to_origin: FakeIntervalTree::new(self.real_to_origin),
+        let interval_tree = FakeIntervalTree::new(self.real_to_origin);
+        let mut table = Vec::new();
+
+        for real in 0.. {
+            match replacement(&self.origins, &interval_tree, real) {
+                Some(range) => table.push(range),
+                None => break,
             }
         }
+
+        QueryEnhancer { table }
+    }
 }
 
-#[derive(Debug)]
-pub struct QueryEnhancer {
-    origins: Vec<usize>,
-    real_to_origin: FakeIntervalTree,
-}
-
-impl QueryEnhancer {
-    /// Returns the query indices that represent this real query index.
-    pub fn replacement(&self, real: u32) -> Range<u32> {
+/// Returns the query indices that represent this real query index.
+fn replacement(
+    origins: &[usize],
+    real_to_origin: &FakeIntervalTree,
+    real: u32,
+) -> Option<Range<u32>>
+{
     let real = real as usize;
 
     // query the fake interval tree with the real query index
-        let (range, (origin, real_length)) = self
-            .real_to_origin
-            .query(real)
-            .expect("real has never been declared");
+    let (range, (origin, real_length)) = real_to_origin.query(real)?;
 
     // if `real` is the end bound of the range
     if (range.start + real_length - 1) == real {
         let mut count = range.len();
         let mut new_origin = origin;
-            for (i, slice) in self.origins[new_origin..].windows(2).enumerate() {
+        for (i, slice) in origins[new_origin..].windows(2).enumerate() {
             let len = slice[1] - slice[0];
             count = count.saturating_sub(len);
             if count == 0 {
@@ -185,25 +187,36 @@ impl QueryEnhancer {
         }
 
         let n = real - range.start;
-            let start = self.origins[origin];
-            let end = self.origins[new_origin + 1];
+        let start = origins[origin];
+        let end = origins[new_origin + 1];
         let remaining = (end - start) - n;
 
-            Range {
+        Some(Range {
             start: (start + n) as u32,
             end: (start + n + remaining) as u32,
-            }
+        })
     } else {
         // just return the origin along with
         // the real position of the word
         let n = real as usize - range.start;
-            let origin = self.origins[origin];
+        let origin = origins[origin];
 
-            Range {
+        Some(Range {
             start: (origin + n) as u32,
             end: (origin + n + 1) as u32,
+        })
     }
-        }
+}
+
+#[derive(Debug)]
+pub struct QueryEnhancer {
+    table: Vec<Range<u32>>,
+}
+
+impl QueryEnhancer {
+    /// Returns the query indices that represent this real query index.
+    pub fn replacement(&self, real: u32) -> Range<u32> {
+        self.table[real as usize].clone()
     }
 }