2 files changed, 43 insertions, 47 deletions

diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index 0329a26db8..c587e9c254 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -64,6 +64,8 @@
 #include <string.h>
 #include <stdlib.h>
 
+#include <algorithm>
+
 #define IS_RAW_DATA(d) ((d)->flags() & QArrayData::RawDataType)
 
 QT_BEGIN_NAMESPACE
@@ -2743,56 +2745,44 @@ static constexpr inline bool isUpperCaseAscii(char c)
     return c >= 'A' && c <= 'Z';
 }
 
+/*
+    Returns true if \a c is an lowercase ASCII letter.
+ */
+static constexpr inline bool isLowerCaseAscii(char c)
+{
+    return c >= 'a' && c <= 'z';
+}
+
 /*!
-    Returns \c true if this byte array contains only ASCII uppercase letters,
-    otherwise returns \c false.
+    Returns \c true if this byte array is uppercase, that is, if
+    it's identical to its toUpper() folding.
+
+    Note that this does \e not mean that the byte array only contains
+    uppercase letters; only that it contains no ASCII lowercase letters.
+
     \since 5.12
 
     \sa isLower(), toUpper()
 */
 bool QByteArray::isUpper() const
 {
-    if (isEmpty())
-        return false;
-
-    const char *d = data();
-
-    for (qsizetype i = 0, max = size(); i < max; ++i) {
-        if (!isUpperCaseAscii(d[i]))
-            return false;
-    }
-
-    return true;
-}
-
-/*
-    Returns true if \a c is an lowercase ASCII letter.
- */
-static constexpr inline bool isLowerCaseAscii(char c)
-{
-    return c >= 'a' && c <= 'z';
+    return std::none_of(begin(), end(), isLowerCaseAscii);
 }
 
 /*!
-    Returns \c true if this byte array contains only lowercase ASCII letters,
-    otherwise returns \c false.
+    Returns \c true if this byte array is lowercase, that is, if
+    it's identical to its toLower() folding.
+
+    Note that this does \e not mean that the byte array only contains
+    lowercase letters; only that it contains no ASCII uppercase letters.
+
     \since 5.12
 
     \sa isUpper(), toLower()
  */
 bool QByteArray::isLower() const
 {
-    if (isEmpty())
-        return false;
-
-    const char *d = data();
-
-    for (qsizetype i = 0, max = size(); i < max; ++i) {
-        if (!isLowerCaseAscii(d[i]))
-            return false;
-    }
-
-    return true;
+    return std::none_of(begin(), end(), isUpperCaseAscii);
 }
 
 /*!
diff --git a/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp b/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp
index b0d9f39b3e..e2d2df70c1 100644
--- a/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp
+++ b/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp
@@ -2234,10 +2234,16 @@ void tst_QByteArray::toUpperLower()
     QFETCH(QByteArray, input);
     QFETCH(QByteArray, upper);
     QFETCH(QByteArray, lower);
+    QVERIFY(upper.isUpper());
+    QVERIFY(lower.isLower());
     QCOMPARE(lower.toLower(), lower);
+    QVERIFY(lower.toLower().isLower());
     QCOMPARE(upper.toUpper(), upper);
+    QVERIFY(upper.toUpper().isUpper());
     QCOMPARE(input.toUpper(), upper);
+    QVERIFY(input.toUpper().isUpper());
     QCOMPARE(input.toLower(), lower);
+    QVERIFY(input.toLower().isLower());
 
     QByteArray copy = input;
     QCOMPARE(std::move(copy).toUpper(), upper);
@@ -2266,12 +2272,12 @@ void tst_QByteArray::toUpperLower()
 
 void tst_QByteArray::isUpper()
 {
-    QVERIFY(!QByteArray().isUpper());
-    QVERIFY(!QByteArray("").isUpper());
+    QVERIFY(QByteArray().isUpper());
+    QVERIFY(QByteArray("").isUpper());
     QVERIFY(QByteArray("TEXT").isUpper());
-    QVERIFY(!QByteArray("\xD0\xDE").isUpper()); // non-ASCII is neither upper nor lower
-    QVERIFY(!QByteArray("\xD7").isUpper());
-    QVERIFY(!QByteArray("\xDF").isUpper());
+    QVERIFY(QByteArray("\xD0\xDE").isUpper());
+    QVERIFY(QByteArray("\xD7").isUpper());
+    QVERIFY(QByteArray("\xDF").isUpper());
     QVERIFY(!QByteArray("text").isUpper());
     QVERIFY(!QByteArray("Text").isUpper());
     QVERIFY(!QByteArray("tExt").isUpper());
@@ -2281,19 +2287,19 @@ void tst_QByteArray::isUpper()
     QVERIFY(!QByteArray("teXT").isUpper());
     QVERIFY(!QByteArray("tEXt").isUpper());
     QVERIFY(!QByteArray("tExT").isUpper());
-    QVERIFY(!QByteArray("@ABYZ[").isUpper());
+    QVERIFY(QByteArray("@ABYZ[").isUpper());
     QVERIFY(!QByteArray("@abyz[").isUpper());
-    QVERIFY(!QByteArray("`ABYZ{").isUpper());
+    QVERIFY(QByteArray("`ABYZ{").isUpper());
     QVERIFY(!QByteArray("`abyz{").isUpper());
 }
 
 void tst_QByteArray::isLower()
 {
-    QVERIFY(!QByteArray().isLower());
-    QVERIFY(!QByteArray("").isLower());
+    QVERIFY(QByteArray().isLower());
+    QVERIFY(QByteArray("").isLower());
     QVERIFY(QByteArray("text").isLower());
-    QVERIFY(!QByteArray("\xE0\xFF").isLower()); // non-ASCII is neither upper nor lower
-    QVERIFY(!QByteArray("\xF7").isLower());
+    QVERIFY(QByteArray("\xE0\xFF").isLower());
+    QVERIFY(QByteArray("\xF7").isLower());
     QVERIFY(!QByteArray("Text").isLower());
     QVERIFY(!QByteArray("tExt").isLower());
     QVERIFY(!QByteArray("teXt").isLower());
@@ -2304,9 +2310,9 @@ void tst_QByteArray::isLower()
     QVERIFY(!QByteArray("tExT").isLower());
     QVERIFY(!QByteArray("TEXT").isLower());
     QVERIFY(!QByteArray("@ABYZ[").isLower());
-    QVERIFY(!QByteArray("@abyz[").isLower());
+    QVERIFY(QByteArray("@abyz[").isLower());
     QVERIFY(!QByteArray("`ABYZ{").isLower());
-    QVERIFY(!QByteArray("`abyz{").isLower());
+    QVERIFY(QByteArray("`abyz{").isLower());
 }
 
 void tst_QByteArray::macTypes()