Optimize CatalogItemsComparator for common case

Prepare cache for faster comparison. ICU uses UTF-16 internally, we can significantly speed up
comparisons by doing string conversion in advance, in O(n) time and space, if the platform's
native representation is UTF-32 or -8 (which it is on non-Windows).

Moreover, the additional processing of removing accelerators is also done only once on all
platforms, resulting in massive speedups on Windows too.

These two optimizations combined result in 10-20x speedup depending on platform.

src/cat_sorting.cpp

@@ -94,6 +94,29 @@ CatalogItemsComparator::CatalogItemsComparator(const Catalog& catalog, const Sor
             m_collator.reset(new unicode::Collator(catalog.GetSourceLanguage(), unicode::Collator::case_insensitive));
             break;
     }
+
+    // Prepare cache for faster comparison. ICU uses UTF-16 internally, we can significantly
+    // speed up comparisons by doing string conversion in advance, in O(n) time and space, if
+    // the platform's native representation is UTF-32 or -8 (which it is on non-Windows).
+    // Moreover, the additional processing of removing accelerators is also done only once
+    // on all platforms, resulting in massive speedups on Windows too.
+    switch (m_order.by)
+    {
+        case SortOrder::By_Source:
+            m_sortKeys.reserve(m_catalog.GetCount());
+            for (auto& i: m_catalog.items())
+                m_sortKeys.push_back(ConvertToSortKey(i->GetString()));
+            break;
+
+        case SortOrder::By_Translation:
+            m_sortKeys.reserve(m_catalog.GetCount());
+            for (auto& i: m_catalog.items())
+                m_sortKeys.push_back(ConvertToSortKey(i->GetTranslation()));
+            break;
+
+        case SortOrder::By_FileOrder:
+            break;
+    }
 }
 
 
@@ -156,16 +179,9 @@ bool CatalogItemsComparator::operator()(int i, int j) const
         }
 
         case SortOrder::By_Source:
-        {
-            auto r = CompareTranslationStrings(a.GetString(), b.GetString());
-            if ( r != 0 )
-                return r < 0;
-            break;
-        }
-
         case SortOrder::By_Translation:
         {
-            auto r = CompareTranslationStrings(a.GetTranslation(), b.GetTranslation());
+            auto r = m_collator->compare(m_sortKeys[i], m_sortKeys[j]);
             if ( r != 0 )
                 return r < 0;
             break;

src/cat_sorting.h

@@ -62,6 +62,7 @@ struct SortOrder
     bool errorsFirst;
 };
 
+
 /**
     Comparator for sorting catalog items by different criteria.
  */
@@ -81,21 +82,35 @@ class CatalogItemsComparator
 protected:
     const CatalogItem& Item(int i) const { return *m_catalog[i]; }
 
-    unicode::Collator::result_type CompareTranslationStrings(wxString a, wxString b) const
+    // Pre-process given string and return it in a form efficient for comparing
+    // with ICU collator. This does two things:
+    //  1. Converts to UTF-16 (matters on non-Windows platforms where wchar_t is UTF-32)
+    //  2. Perform substitution of accelerator characters in the string
+    static str::UCharBuffer ConvertToSortKey(const wxString& a)
     {
-        a.Replace("&", "");
-        a.Replace("_", "");
-
-        b.Replace("&", "");
-        b.Replace("_", "");
-
-        return m_collator->compare(a, b);
+        if (a.find_first_of(L"&_") == wxString::npos)
+        {
+            return str::to_icu(a);
+        }
+        else
+        {
+            wxString a_(a);
+            a_.Replace("&", "");
+            a_.Replace("_", "");
+
+            auto buf = str::to_icu(a_);
+            // on Windows to_icu() returns shallow view of the string, we need to make
+            // a deep copy because a_ is a local temporary variable:
+            buf.ensure_owned();
+            return buf;
+        }
     }
 
 private:
     const Catalog& m_catalog;
     SortOrder m_order;
     std::unique_ptr<unicode::Collator> m_collator;
+    std::vector<str::UCharBuffer> m_sortKeys;
 };
 
 

src/catalog.h

@@ -144,7 +144,8 @@ class CatalogItem
         unsigned GetPluralFormsCount() const;
 
         /// Returns the nth-translation.
-        wxString GetTranslation(unsigned n = 0) const;
+        wxString GetTranslation(unsigned n) const;
+        const wxString& GetTranslation() const { return m_translations[0]; }
 
         /// Returns all translations.
         const wxArrayString& GetTranslations() const { return m_translations; }

src/str_helpers.h

@@ -194,9 +194,22 @@ class UCharBuffer
     operator const UChar*() const { return m_data; }
     UChar* data() { return const_cast<UChar*>(m_data); }
 
-    // available buffer size, only for owned versions, returns 0 for read-only non-owned
+    /// Available buffer size, only for owned versions, returns 0 for read-only non-owned
     int32_t capacity() { return m_capacity; }
 
+    /// Ensure the buffer has a deep copy of the data, if it's not already owned
+    void ensure_owned()
+    {
+        if (m_owned)
+			return;
+        if (m_capacity == -1)
+            m_capacity = u_strlen(m_data) + 1;
+        auto copy = new UChar[m_capacity];
+        memcpy(copy, m_data, m_capacity * sizeof(UChar));
+        m_data = copy;
+        m_owned = true;
+	}
+
 private:
     UCharBuffer(bool owned, const UChar *data, int32_t capacity) : m_owned(owned), m_data(data), m_capacity(capacity) {}
 

src/unicode_helpers.h

@@ -87,6 +87,11 @@ class Collator
         return ucol_strcoll(m_coll, str::to_icu(a), -1, str::to_icu(b), -1);
     }
 
+    result_type compare(const UChar *a, const UChar *b) const
+    {
+        return ucol_strcoll(m_coll, a, -1, b, -1);
+    }
+
     template<typename T>
     bool operator()(const T& a, const T& b) const
     {