Implement UTF-16 to UTF-8 case-insensitive compare and make public

Change-Id: Ied637aece2a7427b8a2dfffd16116cf3645c6359
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

4 files changed, 57 insertions, 3 deletions

diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index 82cdeec1a3..f068c5e94a 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -1,7 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2020 The Qt Company Ltd.
-** Copyright (C) 2018 Intel Corporation.
+** Copyright (C) 2020 Intel Corporation.
 ** Copyright (C) 2019 Mail.ru Group.
 ** Contact: https://www.qt.io/licensing/
 **
@@ -871,6 +871,35 @@ static int ucstricmp(const QChar *a, const QChar *ae, const char *b, const char
     return 1;
 }
 
+// Case-insensitive comparison between a Unicode string and a UTF-8 string
+static int ucstricmp8(const char *utf8, const char *utf8end, const QChar *utf16, const QChar *utf16end)
+{
+    auto src1 = reinterpret_cast<const uchar *>(utf8);
+    auto end1 = reinterpret_cast<const uchar *>(utf8end);
+    QStringIterator src2(utf16, utf16end);
+
+    while (src1 < end1 && src2.hasNext()) {
+        uint uc1;
+        uint *output = &uc1;
+        uchar b = *src1++;
+        int res = QUtf8Functions::fromUtf8<QUtf8BaseTraits>(b, output, src1, end1);
+        if (res < 0) {
+            // decoding error
+            uc1 = QChar::ReplacementCharacter;
+        } else {
+            uc1 = QChar::toCaseFolded(uc1);
+        }
+
+        uint uc2 = QChar::toCaseFolded(src2.next());
+        int diff = uc1 - uc2;   // can't underflow
+        if (diff)
+            return diff;
+    }
+
+    // the shorter string sorts first
+    return (end1 > src1) - int(src2.hasNext());
+}
+
 #if defined(__mips_dsp)
 // From qstring_mips_dsp_asm.S
 extern "C" int qt_ucstrncmp_mips_dsp_asm(const char16_t *a,
@@ -1334,6 +1363,30 @@ int QtPrivate::compareStrings(QLatin1String lhs, QLatin1String rhs, Qt::CaseSens
     return qt_compare_strings(lhs, rhs, cs);
 }
 
+/*!
+    \relates QStringView
+    \internal
+    \since 6.0
+    \overload
+
+    Returns an integer that compares to 0 as \a lhs compares to \a rhs.
+
+    If \a cs is Qt::CaseSensitive (the default), the comparison is case-sensitive;
+    otherwise the comparison is case-insensitive.
+
+    Case-sensitive comparison is based exclusively on the numeric values of the
+    decoded Unicode code points and is very fast, but is not what a human would
+    expect. Consider sorting user-visible strings with
+    QString::localeAwareCompare().
+*/
+int QtPrivate::compareStringsUtf8(const char *u8str, qsizetype u8len, QStringView rhs, Qt::CaseSensitivity cs) noexcept
+{
+    if (cs == Qt::CaseSensitive)
+        return QUtf8::compareUtf8(u8str, u8len, rhs.data(), rhs.size());
+    else
+        return ucstricmp8(u8str, u8str + u8len, rhs.begin(), rhs.end());
+}
+
 #define REHASH(a) \
     if (sl_minus_1 < sizeof(std::size_t) * CHAR_BIT)  \
         hashHaystack -= std::size_t(a) << sl_minus_1; \
diff --git a/src/corelib/text/qstringalgorithms.h b/src/corelib/text/qstringalgorithms.h
index 4a0f7dce9a..c407c54268 100644
--- a/src/corelib/text/qstringalgorithms.h
+++ b/src/corelib/text/qstringalgorithms.h
@@ -62,6 +62,7 @@ Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QStringV
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QStringView   lhs, QLatin1String rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QLatin1String lhs, QStringView   rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStrings(QLatin1String lhs, QLatin1String rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
+Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION int compareStringsUtf8(const char *, qsizetype, QStringView rhs, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
 
 
 Q_REQUIRED_RESULT Q_CORE_EXPORT Q_DECL_PURE_FUNCTION bool startsWith(QStringView   haystack, QStringView   needle, Qt::CaseSensitivity cs = Qt::CaseSensitive) noexcept;
diff --git a/src/corelib/text/qstringconverter.cpp b/src/corelib/text/qstringconverter.cpp
index 8e314ffd34..2111d22b2f 100644
--- a/src/corelib/text/qstringconverter.cpp
+++ b/src/corelib/text/qstringconverter.cpp
@@ -713,7 +713,7 @@ QUtf8::ValidUtf8Result QUtf8::isValidUtf8(const char *chars, qsizetype len)
     return { true, isValidAscii };
 }
 
-int QUtf8::compareUtf8(const char *utf8, qsizetype u8len, const QChar *utf16, qsizetype u16len)
+int QUtf8::compareUtf8(const char *utf8, qsizetype u8len, const QChar *utf16, qsizetype u16len) noexcept
 {
     uint uc1, uc2;
     auto src1 = reinterpret_cast<const uchar *>(utf8);
diff --git a/src/corelib/text/qstringconverter_p.h b/src/corelib/text/qstringconverter_p.h
index 4e1efd3731..3a99a4191a 100644
--- a/src/corelib/text/qstringconverter_p.h
+++ b/src/corelib/text/qstringconverter_p.h
@@ -338,7 +338,7 @@ struct QUtf8
         bool isValidAscii;
     };
     static ValidUtf8Result isValidUtf8(const char *, qsizetype);
-    static int compareUtf8(const char *, qsizetype, const QChar *, qsizetype);
+    static int compareUtf8(const char *, qsizetype, const QChar *, qsizetype) noexcept;
     static int compareUtf8(const char *, qsizetype, QLatin1String s);
 };