Long live Q_(U)INT128_C()!

Compilers that support 128-bit integer types usually don't have
support for 128-bit literals, so provide Q_(U)INT128_C macros and back
them with UDLs. This, of course, only works in C++, so until compilers
provide built-in literals that support C, too, that's all we get.

[ChangeLog][QtCore] Added Q_INT128_C() and Q_UINT128_C() macros to
create qint128 and quint128 literals in a platform-independent way.

Fixes: QTBUG-116822
Change-Id: I4be645baf2e007ee1aa1a27f9b5166671806dc49
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 16433a4a6ed22750adfdb9633149c3bd485c4656)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 321dcd1d1d0fdd627160e882c471529baa6cafa7)

3 files changed, 243 insertions, 8 deletions

diff --git a/src/corelib/global/qtypes.cpp b/src/corelib/global/qtypes.cpp
index 507fd6bbde..19a7541ed1 100644
--- a/src/corelib/global/qtypes.cpp
+++ b/src/corelib/global/qtypes.cpp
@@ -152,7 +152,9 @@ 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 Q_INT128_MIN, Q_INT128_MAX, quint128, QT_SUPPORTS_INT128
+    Literals of this type can be created using the Q_INT128_C() macro.
+
+    \sa Q_INT128_C(), Q_INT128_MIN, Q_INT128_MAX, quint128, QT_SUPPORTS_INT128
 */
 
 /*!
@@ -163,7 +165,9 @@ 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 Q_UINT128_MAX, qint128, QT_SUPPORTS_INT128
+    Literals of this type can be created using the Q_UINT128_C() macro.
+
+    \sa Q_UINT128_C(), Q_UINT128_MAX, qint128, QT_SUPPORTS_INT128
 */
 
 /*!
@@ -174,7 +178,7 @@ 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, Q_INT128_MIN, Q_INT128_MAX, Q_UINT128_MAX
+    \sa qint128, quint128, Q_INT128_C(), Q_UINT128_C(), Q_INT128_MIN, Q_INT128_MAX, Q_UINT128_MAX
 */
 
 /*!
@@ -360,7 +364,7 @@ QT_BEGIN_NAMESPACE
 
     \snippet code/src_corelib_global_qglobal.cpp 8
 
-    \sa qint64, Q_UINT64_C()
+    \sa qint64, Q_UINT64_C(), Q_INT128_C()
 */
 
 /*! \macro quint64 Q_UINT64_C(literal)
@@ -373,7 +377,37 @@ QT_BEGIN_NAMESPACE
 
     \snippet code/src_corelib_global_qglobal.cpp 9
 
-    \sa quint64, Q_INT64_C()
+    \sa quint64, Q_INT64_C(), Q_UINT128_C()
+*/
+
+/*!
+    \macro qint128 Q_INT128_C(literal)
+    \relates <QtTypes>
+    \since 6.6
+
+    Wraps the signed 128-bit integer \a literal in a
+    platform-independent way.
+
+    \note Unlike Q_INT64_C(), this macro is only available in C++, not in C.
+    This is because compilers do not provide these literals as built-ins and C
+    does not have support for user-defined literals.
+
+    \sa qint128, Q_UINT128_C(), Q_INT128_MIN, Q_INT128_MAX, Q_INT64_C(), QT_SUPPORTS_INT128
+*/
+
+/*!
+    \macro quint128 Q_UINT128_C(literal)
+    \relates <QtTypes>
+    \since 6.6
+
+    Wraps the unsigned 128-bit integer \a literal in a
+    platform-independent way.
+
+    \note Unlike Q_UINT64_C(), this macro is only available in C++, not in C.
+    This is because compilers do not provide these literals as built-ins and C
+    does not have support for user-defined literals.
+
+    \sa quint128, Q_INT128_C(), Q_UINT128_MAX, Q_UINT64_C(), QT_SUPPORTS_INT128
 */
 
 /*!
@@ -389,7 +423,7 @@ QT_BEGIN_NAMESPACE
     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
+    \sa Q_INT128_MAX, quint128, Q_UINT128_C, QT_SUPPORTS_INT128
 */
 
 /*!
@@ -402,7 +436,7 @@ QT_BEGIN_NAMESPACE
 
     This macro is available in both C++ and C modes.
 
-    \sa Q_INT128_MAX, qint128, QT_SUPPORTS_INT128
+    \sa Q_INT128_MAX, qint128, Q_INT128_C, QT_SUPPORTS_INT128
 */
 
 /*!
@@ -415,7 +449,7 @@ QT_BEGIN_NAMESPACE
 
     This macro is available in both C++ and C modes.
 
-    \sa Q_INT128_MIN, Q_UINT128_MAX, qint128, QT_SUPPORTS_INT128
+    \sa Q_INT128_MIN, Q_UINT128_MAX, qint128, Q_INT128_C, QT_SUPPORTS_INT128
 */
 
 // Statically check assumptions about the environment we're running
diff --git a/src/corelib/global/qtypes.h b/src/corelib/global/qtypes.h
index cca2263901..41e6025735 100644
--- a/src/corelib/global/qtypes.h
+++ b/src/corelib/global/qtypes.h
@@ -7,6 +7,7 @@
 
 #include <QtCore/qprocessordetection.h>
 #include <QtCore/qtconfigmacros.h>
+#include <QtCore/qassert.h>
 
 #ifdef __cplusplus
 #  include <cstddef>
@@ -80,6 +81,77 @@ __extension__ typedef __uint128_t quint128;
 #  define Q_INT128_MAX QT_C_STYLE_CAST(qint128, (Q_UINT128_MAX / 2))
 #  define Q_INT128_MIN (-Q_INT128_MAX - 1)
 
+#  ifdef __cplusplus
+    namespace QtPrivate::NumberLiterals {
+    namespace detail {
+        template <quint128 accu, int base>
+        constexpr quint128 construct() { return accu; }
+
+        template <quint128 accu, int base, char C, char...Cs>
+        constexpr quint128 construct()
+        {
+            if constexpr (C != '\'') { // ignore digit separators
+                const int digitValue = '0' <= C && C <= '9' ? C - '0'      :
+                                       'a' <= C && C <= 'z' ? C - 'a' + 10 :
+                                       'A' <= C && C <= 'Z' ? C - 'A' + 10 :
+                                       /* else */        -1 ;
+                static_assert(digitValue >= 0 && digitValue < base,
+                              "Invalid character");
+                // accu * base + digitValue <= MAX, but without overflow:
+                static_assert(accu <= (Q_UINT128_MAX - digitValue) / base,
+                              "Overflow occurred");
+                return construct<accu * base + digitValue, base, Cs...>();
+            } else {
+                return construct<accu, base, Cs...>();
+            }
+        }
+
+        template <char C, char...Cs>
+        constexpr quint128 parse0xb()
+        {
+            constexpr quint128 accu = 0;
+            if constexpr (C == 'x' || C == 'X')
+                return construct<accu, 16,   Cs...>(); // base 16, skip 'x'
+            else if constexpr (C == 'b' || C == 'B')
+                return construct<accu, 2,    Cs...>(); // base 2, skip 'b'
+            else
+                return construct<accu, 8, C, Cs...>(); // base 8, include C
+        }
+
+        template <char...Cs>
+        constexpr quint128 parse0()
+        {
+            if constexpr (sizeof...(Cs) == 0) // this was just a literal 0
+                return 0;
+            else
+                return parse0xb<Cs...>();
+        }
+
+        template <char C, char...Cs>
+        constexpr quint128 parse()
+        {
+            if constexpr (C == '0')
+                return parse0<Cs...>(); // base 2, 8, or 16 (or just a literal 0), skip '0'
+            else
+                return construct<0, 10, C, Cs...>(); // initial accu 0, base 10, include C
+        }
+    } // namespace detail
+    template <char...Cs>
+    constexpr quint128 operator""_quint128() noexcept
+    { return QtPrivate::NumberLiterals::detail::parse<Cs...>(); }
+    template <char...Cs>
+    constexpr qint128 operator""_qint128() noexcept
+    { return qint128(QtPrivate::NumberLiterals::detail::parse<Cs...>()); }
+
+    #ifndef Q_UINT128_C // allow qcompilerdetection.h/user override
+    #  define Q_UINT128_C(c) ([]{ using namespace QtPrivate::NumberLiterals; return c ## _quint128; }())
+    #endif
+    #ifndef Q_INT128_C // allow qcompilerdetection.h/user override
+    #  define Q_INT128_C(c)  ([]{ using namespace QtPrivate::NumberLiterals; return c ## _qint128;  }())
+    #endif
+
+    } // namespace QtPrivate::NumberLiterals
+#  endif // __cplusplus
 #endif // QT_SUPPORTS_INT128
 
 #ifndef __cplusplus
diff --git a/tests/auto/corelib/global/qglobal/tst_qglobal.cpp b/tests/auto/corelib/global/qglobal/tst_qglobal.cpp
index edfa59ebf1..bc96c0d9f0 100644
--- a/tests/auto/corelib/global/qglobal/tst_qglobal.cpp
+++ b/tests/auto/corelib/global/qglobal/tst_qglobal.cpp
@@ -497,6 +497,135 @@ void tst_QGlobal::int128Literals()
     QCOMPARE_EQ(tst_qint128_min(), Q_INT128_MIN);
     QCOMPARE_EQ(tst_qint128_max(), Q_INT128_MAX);
     QCOMPARE_EQ(tst_quint128_max(), Q_UINT128_MAX);
+    {
+        #define CHECK_S(x) COMPARE_EQ(Q_INT128_C(x), Q_INT64_C(x), qint128)
+        #define CHECK_U(x) COMPARE_EQ(Q_UINT128_C(x), Q_UINT64_C(x), quint128);
+        #define CHECK(x) do { CHECK_S(x); CHECK_U(x); } while (0)
+        // basics:
+        CHECK(0);
+        CHECK(1);
+        CHECK_S(-1);
+        QCOMPARE_EQ(Q_INT64_C(9223372036854775807), std::numeric_limits<qint64>::max());
+        CHECK(9223372036854775807); // LLONG_MAX
+        // Q_INT64_C(-9223372036854775808) gives -Wimplicitly-unsigned-literal on GCC, so use numeric_limits:
+        {
+            constexpr auto i = Q_INT128_C(-9223372036854775808); // LLONG_MIN
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            QCOMPARE_EQ(i, std::numeric_limits<qint64>::min());
+        }
+        // actual 128-bit numbers
+        {
+            constexpr auto i = Q_INT128_C( 9223372036854775808); // LLONG_MAX + 1
+            constexpr auto u = Q_UINT128_C(9223372036854775808); // LLONG_MAX + 1
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            static_assert(std::is_same_v<decltype(u), const quint128>);
+            QCOMPARE_EQ(i, qint128{ std::numeric_limits<qint64>::max()} + 1);
+            QCOMPARE_EQ(u, quint128{std::numeric_limits<qint64>::max()} + 1);
+        }
+        {
+            constexpr auto i = Q_INT128_C(-9223372036854775809); // LLONG_MIN - 1
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            QCOMPARE_EQ(i, qint128{std::numeric_limits<qint64>::min()} - 1);
+        }
+        {
+            constexpr auto i = Q_INT128_C( 18446744073709551616); // ULLONG_MAX + 1
+            constexpr auto u = Q_UINT128_C(18446744073709551616);
+            constexpr auto expected = qint128{1} << 64;
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            static_assert(std::is_same_v<decltype(expected), const qint128>);
+            static_assert(std::is_same_v<decltype(u), const quint128>);
+            QCOMPARE_EQ(i, expected);
+            QCOMPARE_EQ(u, quint128{expected});
+        }
+        {
+            // compilers don't let one write signed _MIN literals, so use MIN + 1:
+            // Q_INT128_C(-170141183460469231731687303715884105728) gives
+            //   ERROR: ~~~ outside range of representable values of type qint128
+            // This is because the unary minus is technically speaking not part of
+            // the literal, but called on the result of the literal.
+            constexpr auto i = Q_INT128_C(-170141183460469231731687303715884105727); // 128-bit MIN + 1
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            QCOMPARE_EQ(i, std::numeric_limits<qint128>::min() + 1);
+        }
+        {
+            constexpr auto i = Q_INT128_C( 170141183460469231731687303715884105727); // MAX
+            constexpr auto u = Q_UINT128_C(340282366920938463463374607431768211455); // UMAX
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            static_assert(std::is_same_v<decltype(u), const quint128>);
+            QCOMPARE_EQ(i, std::numeric_limits<qint128>::max());
+            QCOMPARE_EQ(u, std::numeric_limits<quint128>::max());
+            QCOMPARE_EQ(u, Q_UINT128_C(-1));
+        }
+
+        // binary literals:
+        CHECK(0b0);
+        CHECK(0b1);
+        CHECK_S(-0b1);
+        CHECK(0b01);
+        CHECK(0b10);
+        CHECK(0b1'1); // with digit separator
+        CHECK(0b0111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111);
+        //bytes |---1---| |---2---| |---3---| |---4---| |---5---| |---6---| |---7---| |---8---|
+        {
+            //                        bytes: |---1---| |---2---| |---3---| |---4---| |---5---| |---6---| |---7---| |---8---| |---9---| |--10---| |--11---| |--12---| |--13---| |--14---| |--15---| |--16---|
+            constexpr auto i = Q_INT128_C( 0b0111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111);
+            constexpr auto u = Q_UINT128_C(0b1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111'1111);
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            static_assert(std::is_same_v<decltype(u), const quint128>);
+            QCOMPARE_EQ(i, std::numeric_limits<qint128>::max());
+            QCOMPARE_EQ(u, std::numeric_limits<quint128>::max());
+            QCOMPARE_EQ(u, Q_UINT128_C(-0b1));
+        }
+
+        // octal literals:
+        CHECK(00);
+        CHECK(01);
+        CHECK(02);
+        CHECK(03);
+        CHECK(04);
+        CHECK(05);
+        CHECK(06);
+        CHECK(07);
+        CHECK_S(-01);
+        CHECK(010);
+        CHECK_S(-01'0); // with digit separator
+        CHECK(07'7777'7777'7777'7777'7777); // LLONG_MAX
+        {
+            //                        bits: 120| 108|  96|  84|  72|  60|  48|  36|  24|  12|   0|
+            constexpr auto i = Q_INT128_C( 0177'7777'7777'7777'7777'7777'7777'7777'7777'7777'7777);
+            constexpr auto u = Q_UINT128_C(0377'7777'7777'7777'7777'7777'7777'7777'7777'7777'7777);
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            static_assert(std::is_same_v<decltype(u), const quint128>);
+            QCOMPARE_EQ(i, std::numeric_limits<qint128>::max());
+            QCOMPARE_EQ(u, std::numeric_limits<quint128>::max());
+            QCOMPARE_EQ(u, Q_UINT128_C(-01));
+        }
+
+        // hex literals:
+        CHECK(0x0);
+        CHECK(0x1);
+        CHECK(0x9);
+        CHECK(0xA);
+        CHECK(0xB);
+        CHECK(0xC);
+        CHECK(0xD);
+        CHECK(0xE);
+        CHECK(0x0F);
+        CHECK(0x10);
+        CHECK_S(-0x1);
+        CHECK_S(-0x1'0); // with digit separator
+        CHECK(0x7FFF'FFFF'FFFF'FFFF);
+        {
+            constexpr auto i = Q_INT128_C( 0x7FFF'FFFF'FFFF'FFFF'FFFF'FFFF'FFFF'FFFF);
+            constexpr auto u = Q_UINT128_C(0xFFFF'FFFF'FFFF'FFFF'FFFF'FFFF'FFFF'FFFF);
+            static_assert(std::is_same_v<decltype(i), const qint128>);
+            static_assert(std::is_same_v<decltype(u), const quint128>);
+            QCOMPARE_EQ(i, std::numeric_limits<qint128>::max());
+            QCOMPARE_EQ(u, std::numeric_limits<quint128>::max());
+            QCOMPARE_EQ(Q_UINT128_C(-1), u);
+        }
+    #undef CHECK
+    }
 #undef COMPARE_EQ
 #else
     QSKIP("This test requires 128-bit integer support enabled in the compiler.");