1 files changed, 35 insertions, 0 deletions
diff --git a/src/corelib/global/qnumeric_p.h b/src/corelib/global/qnumeric_p.h
index 7c65b67b7a..f5beb4d38d 100644
--- a/src/corelib/global/qnumeric_p.h
+++ b/src/corelib/global/qnumeric_p.h
@@ -314,6 +314,41 @@ template <auto V2, typename T> bool mul_overflow(T v1, T *r)
 }
 #endif // Q_CLANG_QDOC
 
+/*
+    Safely narrows \a x to \c{To}. Let \c L be
+    \c{std::numeric_limit<To>::min()} and \c H be \c{std::numeric_limit<To>::max()}.
+
+    If \a x is less than L, returns L. If \a x is greater than H,
+    returns H. Otherwise, returns \c{To(x)}.
+*/
+template <typename To, typename From>
+static constexpr auto qt_saturate(From x)
+{
+    static_assert(std::is_integral_v<To>);
+    static_assert(std::is_integral_v<From>);
+
+    [[maybe_unused]]
+    constexpr auto Lo = (std::numeric_limits<To>::min)();
+    constexpr auto Hi = (std::numeric_limits<To>::max)();
+
+    if constexpr (std::is_signed_v<From> == std::is_signed_v<To>) {
+        // same signedness, we can accept regular integer conversion rules
+        return x < Lo  ? Lo :
+               x > Hi  ? Hi :
+               /*else*/  To(x);
+    } else {
+        if constexpr (std::is_signed_v<From>) { // ie. !is_signed_v<To>
+            if (x < From{0})
+                return To{0};
+        }
+
+        // from here on, x >= 0
+        using FromU = std::make_unsigned_t<From>;
+        using ToU = std::make_unsigned_t<To>;
+        return FromU(x) > ToU(Hi) ? Hi : To(x); // assumes Hi >= 0
+    }
+}
+
 QT_END_NAMESPACE
 
 #endif // QNUMERIC_P_H