refactor(math-kern): call hb_bsearch_impl instead of raw binary search

src/hb-ot-math-table.hh

@@ -347,22 +347,17 @@ struct MathKern
     /* According to OpenType spec (v1.9), except for the boundary cases, the index
      * chosen for kern value should be i such that
      *    correctionHeight[i-1] <= correction_height < correctionHeight[i]
-     * We can just use the binary search algorithm of std::upper_bound(), which
-     * matches the spec, including for the boundary cases.
+     * We can use the binary search algorithm of std::upper_bound(). Or, we can
+     * use the internal hb_bsearch_impl.
      */
-    unsigned int i = 0;
-    unsigned int count = heightCount;
-    while (count > 0)
-    {
-      unsigned int half = count / 2;
-      hb_position_t height = correctionHeight[i + half].get_y_value (font, this);
-      if (sign * height <= sign * correction_height)
-      {
-	i += half + 1;
-	count -= half + 1;
-      } else
-	count = half;
-    }
+    unsigned int pos;
+    auto cmp = +[](const void* key, const void* p,
+                   int sign, hb_font_t* font, const MathKern* mathKern) -> int {
+      return sign * *(hb_position_t*)key - sign * ((MathValueRecord*)p)->get_y_value(font, mathKern);
+    };
+    unsigned int i = hb_bsearch_impl(&pos, correction_height, correctionHeight,
+                                     heightCount, MathValueRecord::static_size,
+                                     cmp, sign, font, this) ? pos + 1 : pos;
     return kernValue[i].get_x_value (font, this);
   }