Long live Q_(U)INT128_MIN/MAX!

Since compilers don't provide such macros, do it ourselves.

In order to test these macros, add ad-hoc specializations of
QTest::toString() for qint128 and quint128 locally to the test. Turns
out it's not too hard to write them, so we might move them to a public
header, yet.

Pick-to: 6.6
Change-Id: I1483f3af2ccec6038e1c780649f9ffe413bb59ef
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qtypes.cpp

@@ -152,7 +152,7 @@ QT_BEGIN_NAMESPACE
     Typedef for \c{__int128} on platforms that support it (Qt defines the macro
     \l QT_SUPPORTS_INT128 if this is the case).
 
-    \sa quint128, QT_SUPPORTS_INT128
+    \sa Q_INT128_MIN, Q_INT128_MAX, quint128, QT_SUPPORTS_INT128
 */
 
 /*!
@@ -163,7 +163,7 @@ QT_BEGIN_NAMESPACE
     Typedef for \c{unsigned __int128} on platforms that support it (Qt defines
     the macro \l QT_SUPPORTS_INT128 if this is the case).
 
-    \sa qint128, QT_SUPPORTS_INT128
+    \sa Q_UINT128_MAX, qint128, QT_SUPPORTS_INT128
 */
 
 /*!
@@ -174,7 +174,7 @@ QT_BEGIN_NAMESPACE
     Qt defines this macro as well as the \l qint128 and \l quint128 types if
     the platform has support for 128-bit integer types.
 
-    \sa qint128, quint128
+    \sa qint128, quint128, Q_INT128_MIN, Q_INT128_MAX, Q_UINT128_MAX
 */
 
 /*!
@@ -376,6 +376,48 @@ QT_BEGIN_NAMESPACE
     \sa quint64, Q_INT64_C()
 */
 
+/*!
+    \macro Q_UINT128_MAX
+    \relates <QtTypes>
+    \since 6.6
+
+    This macro expands to a compile-time constant representing the
+    maximum value representable in a \l quint128.
+
+    This macro is available in both C++ and C modes.
+
+    The minimum of \l quint128 is 0 (zero), so a \c{Q_UINT128_MIN} is neither
+    needed nor provided.
+
+    \sa Q_INT128_MAX, quint128, QT_SUPPORTS_INT128
+*/
+
+/*!
+    \macro Q_INT128_MIN
+    \relates <QtTypes>
+    \since 6.6
+
+    This macro expands to a compile-time constant representing the
+    minimum value representable in a \l qint128.
+
+    This macro is available in both C++ and C modes.
+
+    \sa Q_INT128_MAX, qint128, QT_SUPPORTS_INT128
+*/
+
+/*!
+    \macro Q_INT128_MAX
+    \relates <QtTypes>
+    \since 6.6
+
+    This macro expands to a compile-time constant representing the
+    maximum value representable in a \l qint128.
+
+    This macro is available in both C++ and C modes.
+
+    \sa Q_INT128_MIN, Q_UINT128_MAX, qint128, QT_SUPPORTS_INT128
+*/
+
 // Statically check assumptions about the environment we're running
 // in. The idea here is to error or warn if otherwise implicit Qt
 // assumptions are not fulfilled on new hardware or compilers
@@ -439,9 +481,10 @@ static_assert(sizeof(qint128) == 16, "Internal error, qint128 is misdefined");
 #ifdef QT_SUPPORTS_INT128
 // check that numeric_limits works:
 // This fails here for GCC 9, but succeeds on Clang and GCC >= 11
+// However, all tests in tst_qglobal::int128Literals() pass for GCC 9, too,
 // so just suppress the check for older GCC:
 #  if !defined(Q_CC_GNU_ONLY) || Q_CC_GNU >= 1100
-static_assert(std::numeric_limits<quint128>::max() == qint128(-1));
+static_assert(std::numeric_limits<quint128>::max() == Q_UINT128_MAX);
 #  endif
 #endif
 

src/corelib/global/qtypes.h

@@ -67,7 +67,20 @@ typedef quint64 qulonglong;
 #if defined(QT_SUPPORTS_INT128)
 __extension__ typedef __int128_t qint128;
 __extension__ typedef __uint128_t quint128;
-#endif
+
+// limits:
+#  ifdef __cplusplus /* need to avoid c-style-casts in C++ mode */
+#    define QT_C_STYLE_CAST(type, x) static_cast<type>(x)
+#  else /* but C doesn't have constructor-style casts */
+#    define QT_C_STYLE_CAST(type, x) ((type)x)
+#  endif
+#  ifndef Q_UINT128_MAX /* allow qcompilerdetection.h/user override */
+#    define Q_UINT128_MAX QT_C_STYLE_CAST(quint128, -1)
+#  endif
+#  define Q_INT128_MAX QT_C_STYLE_CAST(qint128, (Q_UINT128_MAX / 2))
+#  define Q_INT128_MIN (-Q_INT128_MAX - 1)
+
+#endif // QT_SUPPORTS_INT128
 
 #ifndef __cplusplus
 // In C++ mode, we define below using QIntegerForSize template

tests/auto/corelib/global/qglobal/qglobal.c

@@ -59,6 +59,12 @@ void tst_GlobalTypes()
 #endif /* QT_SUPPORTS_INT128 */
 }
 
+#if QT_SUPPORTS_INT128
+qint128 tst_qint128_min() { return Q_INT128_MIN + 0; }
+qint128 tst_qint128_max() { return 0 + Q_INT128_MAX; }
+quint128 tst_quint128_max() { return Q_UINT128_MAX - 1 + 1; }
+#endif
+
 /* Qt version */
 int tst_QtVersion()
 {

tests/auto/corelib/global/qglobal/tst_qglobal.cpp

@@ -12,8 +12,49 @@
 #include <QString>
 #include <QtVersion>
 
+#include <array>
 #include <cmath>
 
+QT_BEGIN_NAMESPACE
+namespace QTest {
+#ifdef QT_SUPPORTS_INT128
+namespace detail {
+    char *i128ToStringHelper(std::array<char, 64> &buffer, quint128 n)
+    {
+        auto dst = buffer.data() + buffer.size();
+        *--dst = '\0'; // NUL-terminate
+        if (n == 0) {
+            *--dst = '0'; // and done
+        } else {
+            while (n != 0) {
+                *--dst = "0123456789"[n % 10];
+                n /= 10;
+            }
+        }
+        return dst;
+    }
+}
+template <>
+char *toString(const qint128 &i)
+{
+    if (i == std::numeric_limits<qint128>::min()) // -i is not representable, hardcode:
+        return qstrdup("-170141183460469231731687303715884105728");
+    std::array<char, 64> buffer;
+    auto dst = detail::i128ToStringHelper(buffer, i < 0 ? -i : i);
+    if (i < 0)
+        *--dst = '-';
+    return qstrdup(dst);
+}
+template <>
+char *toString(const quint128 &i)
+{
+    std::array<char, 64> buffer;
+    return qstrdup(detail::i128ToStringHelper(buffer, i));
+}
+#endif // QT_SUPPORTS_INT128
+} // namespace QTest
+QT_END_NAMESPACE
+
 class tst_QGlobal: public QObject
 {
     Q_OBJECT
@@ -30,6 +71,7 @@ private slots:
     void qCoreAppStartupFunction();
     void qCoreAppStartupFunctionRestart();
     void integerForSize();
+    void int128Literals();
     void buildAbiEndianness();
     void testqOverload();
     void testqMinMax();
@@ -46,6 +88,12 @@ extern "C" {        // functions in qglobal.c
 void tst_GlobalTypes();
 int tst_QtVersion();
 const char *tst_qVersion();
+#if QT_SUPPORTS_INT128
+qint128 tst_qint128_min();
+qint128 tst_qint128_max();
+quint128 tst_quint128_max();
+#endif
+
 }
 
 void tst_QGlobal::cMode()
@@ -437,6 +485,26 @@ void tst_QGlobal::integerForSize()
 #endif
 }
 
+void tst_QGlobal::int128Literals()
+{
+#ifdef QT_SUPPORTS_INT128
+#define COMPARE_EQ(lhs, rhs, Expected128) do { \
+        constexpr auto lhs_ = lhs; \
+        static_assert(std::is_same_v<std::remove_cv_t<decltype(lhs_)>, Expected128>); \
+        QCOMPARE_EQ(lhs_, rhs); \
+    } while (0)
+    COMPARE_EQ(Q_INT128_MIN, std::numeric_limits<qint128>::min(), qint128);
+    COMPARE_EQ(Q_INT128_MAX, std::numeric_limits<qint128>::max(), qint128);
+    COMPARE_EQ(Q_UINT128_MAX, std::numeric_limits<quint128>::max(), quint128);
+    QCOMPARE_EQ(tst_qint128_min(), Q_INT128_MIN);
+    QCOMPARE_EQ(tst_qint128_max(), Q_INT128_MAX);
+    QCOMPARE_EQ(tst_quint128_max(), Q_UINT128_MAX);
+#undef COMPARE_EQ
+#else
+    QSKIP("This test requires 128-bit integer support enabled in the compiler.");
+#endif
+}
+
 typedef QPair<const char *, const char *> stringpair;
 Q_DECLARE_METATYPE(stringpair)