Q{Any,}StringView: optimize lengthHelperContainer for the runtime

Deduplicate it in the process by moving to qstringalgorithms.h.

In non-constexpr contexts, both GCC and Clang were giving up in
pre-calculating the length if the UTF-16 string literal was too big. For
the old code, that was 14 and 16 characters respectively. That number
can be raised by adding some Q_ALWAYS_INLINE and (for GCC's case),
replacing std::char_traits::find() with std::find(). If that limit is
exceeded, we call the newly introduced qustrnlen() function.

qustrnlen() is just qustrchr(), like qstrnlen() is just memchr(). But it
is introduced as a separate function so we could change implementation
if we ever wished to, plus QStringView is only forward-declared at this
point.

Change-Id: Ieab617d69f3b4b54ab30fffd175c560d926db1c3
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 2 insertions, 16 deletions

diff --git a/src/corelib/text/qstringview.h b/src/corelib/text/qstringview.h
index e4c0c4dd8d..a6f217d2a5 100644
--- a/src/corelib/text/qstringview.h
+++ b/src/corelib/text/qstringview.h
@@ -116,20 +116,6 @@ private:
         return QtPrivate::qustrlen(reinterpret_cast<const char16_t *>(str));
     }
 
-    template <typename Container>
-    static constexpr qsizetype lengthHelperContainer(const Container &c) noexcept
-    {
-        return qsizetype(std::size(c));
-    }
-
-    template <typename Char, size_t N>
-    static constexpr qsizetype lengthHelperContainer(const Char (&str)[N]) noexcept
-    {
-        const auto it = std::char_traits<Char>::find(str, N, Char(0));
-        const auto end = it ? it : std::end(str);
-        return qsizetype(std::distance(str, end));
-    }
-
     template <typename Char>
     static const storage_type *castHelper(const Char *str) noexcept
     { return reinterpret_cast<const storage_type*>(str); }
@@ -178,8 +164,8 @@ public:
 #endif
 
     template <typename Container, if_compatible_container<Container> = true>
-    constexpr QStringView(const Container &c) noexcept
-        : QStringView(std::data(c), lengthHelperContainer(c)) {}
+    constexpr Q_ALWAYS_INLINE QStringView(const Container &c) noexcept
+        : QStringView(std::data(c), QtPrivate::lengthHelperContainer(c)) {}
 
     template <typename Char, size_t Size, if_compatible_char<Char> = true>
     [[nodiscard]] constexpr static QStringView fromArray(const Char (&string)[Size]) noexcept