QUuid: add fromString(QStringView/QLatin1String)

As for the formatting code, de-duplicate the parsing code by only
parsing char*s, converting QChars to Latin-1 first in a small buffer.

The QUuid(const char*) ctor performed no length checking, relying
instead on the checks performed within _q_uuidFromHex(), which
includes an implicit check for premature end (because NUL is not
a valid token for the parser).

The (QString) and (QByteArray) ctors did perform length checking.
To the extent possible, this is removed, since it is handled by
_q_uuidFromHex(). Failure cases need not be optimized. Only the
QLatin1String overload needs to do some checking, because views in
general are not NUL-terminated. The QStringView overload can just
append a NUL when it converts to Latin-1.

The only check I added to _q_uuidFromHex() is that for src ==
nullptr. It would otherwise be duplicated in several callers.

While touching the internal functions, port to passing and returning
by value.

Saves 1.6KiB in text size on optimized GCC 6.1 Linux AMD64 builds,
even though we added new API.

Port some users to the new functions. Expand fromString() test.

[ChangeLog][QtCore][QUuid] Added fromString(QStringView/QLatin1String).

Change-Id: I519339419129550c86e0ea80514865cd6a768f5d
Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

2 files changed, 96 insertions, 62 deletions

diff --git a/src/corelib/plugin/quuid.cpp b/src/corelib/plugin/quuid.cpp
index 3b010b3ae1..c9644c73d3 100644
--- a/src/corelib/plugin/quuid.cpp
+++ b/src/corelib/plugin/quuid.cpp
@@ -67,8 +67,8 @@ void _q_toHex(char *&dst, Integral value)
     }
 }
 
-template <class Char, class Integral>
-bool _q_fromHex(const Char *&src, Integral &value)
+template <class Integral>
+bool _q_fromHex(const char *&src, Integral &value)
 {
     value = 0;
 
@@ -102,30 +102,46 @@ static char *_q_uuidToHex(const QUuid &uuid, char *dst)
     return dst;
 }
 
-template <class Char>
-bool _q_uuidFromHex(const Char *&src, uint &d1, ushort &d2, ushort &d3, uchar (&d4)[8])
+/*!
+    \internal
+
+    Parses the string representation of a UUID (with optional surrounding "{}")
+    by reading at most MaxStringUuidLength (38) characters from \a src, which
+    may be \c nullptr. Stops at the first invalid character (which includes a
+    premature NUL).
+
+    Returns the successfully parsed QUuid, or a null QUuid in case of failure.
+*/
+Q_NEVER_INLINE
+static QUuid _q_uuidFromHex(const char *src)
 {
-    if (*src == Char('{'))
-        src++;
-    if (!_q_fromHex(src, d1)
-            || *src++ != Char('-')
-            || !_q_fromHex(src, d2)
-            || *src++ != Char('-')
-            || !_q_fromHex(src, d3)
-            || *src++ != Char('-')
-            || !_q_fromHex(src, d4[0])
-            || !_q_fromHex(src, d4[1])
-            || *src++ != Char('-')
-            || !_q_fromHex(src, d4[2])
-            || !_q_fromHex(src, d4[3])
-            || !_q_fromHex(src, d4[4])
-            || !_q_fromHex(src, d4[5])
-            || !_q_fromHex(src, d4[6])
-            || !_q_fromHex(src, d4[7])) {
-        return false;
+    uint d1;
+    ushort d2, d3;
+    uchar d4[8];
+
+    if (src) {
+        if (*src == '{')
+            src++;
+        if (Q_LIKELY(   _q_fromHex(src, d1)
+                     && *src++ == '-'
+                     && _q_fromHex(src, d2)
+                     && *src++ == '-'
+                     && _q_fromHex(src, d3)
+                     && *src++ == '-'
+                     && _q_fromHex(src, d4[0])
+                     && _q_fromHex(src, d4[1])
+                     && *src++ == '-'
+                     && _q_fromHex(src, d4[2])
+                     && _q_fromHex(src, d4[3])
+                     && _q_fromHex(src, d4[4])
+                     && _q_fromHex(src, d4[5])
+                     && _q_fromHex(src, d4[6])
+                     && _q_fromHex(src, d4[7]))) {
+            return QUuid(d1, d2, d3, d4[0], d4[1], d4[2], d4[3], d4[4], d4[5], d4[6], d4[7]);
+        }
     }
 
-    return true;
+    return QUuid();
 }
 
 #ifndef QT_BOOTSTRAPPED
@@ -336,7 +352,7 @@ static QUuid createFromName(const QUuid &ns, const QByteArray &baseData, QCrypto
 /*!
   Creates a QUuid object from the string \a text, which must be
   formatted as five hex fields separated by '-', e.g.,
-  "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where 'x' is a hex
+  "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where each 'x' is a hex
   digit. The curly braces shown here are optional, but it is normal to
   include them. If the conversion fails, a null UUID is created.  See
   toString() for an explanation of how the five hex fields map to the
@@ -345,45 +361,76 @@ static QUuid createFromName(const QUuid &ns, const QByteArray &baseData, QCrypto
     \sa toString(), QUuid()
 */
 QUuid::QUuid(const QString &text)
+    : QUuid(fromString(text))
 {
-    if (text.length() < 36) {
-        *this = QUuid();
-        return;
-    }
+}
+
+/*!
+    \since 5.10
 
-    const ushort *data = reinterpret_cast<const ushort *>(text.unicode());
+    Creates a QUuid object from the string \a text, which must be
+    formatted as five hex fields separated by '-', e.g.,
+    "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where each 'x' is a hex
+    digit. The curly braces shown here are optional, but it is normal to
+    include them. If the conversion fails, a null UUID is returned.  See
+    toString() for an explanation of how the five hex fields map to the
+    public data members in QUuid.
 
-    if (*data == '{' && text.length() < 37) {
-        *this = QUuid();
-        return;
-    }
+    \sa toString(), QUuid()
+*/
+QUuid QUuid::fromString(QStringView text) Q_DECL_NOTHROW
+{
+    if (text.size() > MaxStringUuidLength)
+        text = text.left(MaxStringUuidLength); // text.truncate(MaxStringUuidLength);
 
-    if (!_q_uuidFromHex(data, data1, data2, data3, data4)) {
-        *this = QUuid();
-        return;
+    char latin1[MaxStringUuidLength + 1];
+    char *dst = latin1;
+
+    for (QChar ch : text)
+        *dst++ = ch.toLatin1();
+
+    *dst++ = '\0'; // don't read garbage as potentially valid data
+
+    return _q_uuidFromHex(latin1);
+}
+
+/*!
+    \since 5.10
+    \overload
+
+    Creates a QUuid object from the string \a text, which must be
+    formatted as five hex fields separated by '-', e.g.,
+    "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where each 'x' is a hex
+    digit. The curly braces shown here are optional, but it is normal to
+    include them. If the conversion fails, a null UUID is returned.  See
+    toString() for an explanation of how the five hex fields map to the
+    public data members in QUuid.
+
+    \sa toString(), QUuid()
+*/
+QUuid QUuid::fromString(QLatin1String text) Q_DECL_NOTHROW
+{
+    if (Q_UNLIKELY(text.size() < MaxStringUuidLength - 2
+                   || (text.front() == QLatin1Char('{') && text.size() < MaxStringUuidLength - 1))) {
+        // Too short. Don't call _q_uuidFromHex(); QL1Ss need not be NUL-terminated,
+        // and we don't want to read trailing garbage as potentially valid data.
+        text = QLatin1String();
     }
+    return _q_uuidFromHex(text.data());
 }
 
 /*!
     \internal
 */
 QUuid::QUuid(const char *text)
+    : QUuid(_q_uuidFromHex(text))
 {
-    if (!text) {
-        *this = QUuid();
-        return;
-    }
-
-    if (!_q_uuidFromHex(text, data1, data2, data3, data4)) {
-        *this = QUuid();
-        return;
-    }
 }
 
 /*!
   Creates a QUuid object from the QByteArray \a text, which must be
   formatted as five hex fields separated by '-', e.g.,
-  "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where 'x' is a hex
+  "{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}" where each 'x' is a hex
   digit. The curly braces shown here are optional, but it is normal to
   include them. If the conversion fails, a null UUID is created.  See
   toByteArray() for an explanation of how the five hex fields map to the
@@ -394,23 +441,8 @@ QUuid::QUuid(const char *text)
     \sa toByteArray(), QUuid()
 */
 QUuid::QUuid(const QByteArray &text)
+    : QUuid(fromString(QLatin1String(text.data(), text.size())))
 {
-    if (text.length() < 36) {
-        *this = QUuid();
-        return;
-    }
-
-    const char *data = text.constData();
-
-    if (*data == '{' && text.length() < 37) {
-        *this = QUuid();
-        return;
-    }
-
-    if (!_q_uuidFromHex(data, data1, data2, data3, data4)) {
-        *this = QUuid();
-        return;
-    }
 }
 
 /*!
diff --git a/src/corelib/plugin/quuid.h b/src/corelib/plugin/quuid.h
index 264f572993..d975528dcf 100644
--- a/src/corelib/plugin/quuid.h
+++ b/src/corelib/plugin/quuid.h
@@ -116,6 +116,8 @@ public:
 #endif
 
     QUuid(const QString &);
+    static QUuid fromString(QStringView string) Q_DECL_NOTHROW;
+    static QUuid fromString(QLatin1String string) Q_DECL_NOTHROW;
     QUuid(const char *);
     QString toString() const;
     QUuid(const QByteArray &);