Rename qt_saturate to q26::saturate_cast

C++26 adds std::saturate_cast, so follow the established pattern of
other similar "backported" APIs. The old name is left around while
we port other submodules.

While at it, move qt_saturate's tests to the qnumeric test.

Change-Id: I653a2e3d936081378298a9c8e51e7c1a2d438d83
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 7447ad503330ed176cf369792ffb33b7e00a58d3)
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/CMakeLists.txt

@@ -100,6 +100,7 @@ qt_internal_add_module(Core
         global/q23functional.h
         global/q23utility.cpp # remove once we have a user that tests this
         global/q23utility.h
+        global/q26numeric.h
         global/qxpfunctional.h
         global/qxptype_traits.h
         global/qversiontagging.h

src/corelib/global/q26numeric.h

@@ -0,0 +1,69 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+#ifndef Q26NUMERIC_H
+#define Q26NUMERIC_H
+
+#include <QtCore/qglobal.h>
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
+// will remove them once Qt depends on the C++ version that supports
+// them in namespace std. There will be NO deprecation warning, the
+// definitions will JUST go away.
+//
+// If you can't agree to these terms, don't use these definitions!
+//
+// We mean it.
+//
+
+#include <numeric>
+#include <limits>
+#include <type_traits>
+
+QT_BEGIN_NAMESPACE
+
+namespace q26 {
+
+// Like std::saturate_cast
+#ifdef __cpp_lib_saturation_arithmetic
+using std::saturate_cast;
+#else
+template <typename To, typename From>
+constexpr auto saturate_cast(From x)
+{
+    static_assert(std::is_integral_v<To>);
+    static_assert(std::is_integral_v<From>);
+
+    [[maybe_unused]]
+    constexpr auto Lo = (std::numeric_limits<To>::min)();
+    constexpr auto Hi = (std::numeric_limits<To>::max)();
+
+    if constexpr (std::is_signed_v<From> == std::is_signed_v<To>) {
+        // same signedness, we can accept regular integer conversion rules
+        return x < Lo  ? Lo :
+               x > Hi  ? Hi :
+               /*else*/  To(x);
+    } else {
+        if constexpr (std::is_signed_v<From>) { // ie. !is_signed_v<To>
+            if (x < From{0})
+                return To{0};
+        }
+
+        // from here on, x >= 0
+        using FromU = std::make_unsigned_t<From>;
+        using ToU = std::make_unsigned_t<To>;
+        return FromU(x) > ToU(Hi) ? Hi : To(x); // assumes Hi >= 0
+    }
+}
+#endif // __cpp_lib_saturation_arithmetic
+
+} // namespace q26
+
+QT_END_NAMESPACE
+
+#endif /* Q26NUMERIC_H */

src/corelib/global/qnumeric.cpp

@@ -458,39 +458,4 @@ Q_CORE_EXPORT quint64 qFloatDistance(double a, double b)
     Returns true if the absolute value of \a f is within 0.00001f of 0.0.
 */
 
-namespace QtNumericTests {
-
-template <typename T> static constexpr T max = std::numeric_limits<T>::max();
-template <typename T> static constexpr T min = std::numeric_limits<T>::min();
-
-static_assert(qt_saturate<short>(max<unsigned>) == max<short>);
-static_assert(qt_saturate<int>(max<unsigned>) == max<int>);
-static_assert(qt_saturate<qint64>(max<unsigned>) == qint64(max<unsigned>));
-
-static_assert(qt_saturate<short>(max<int>) == max<short>);
-static_assert(qt_saturate<unsigned>(max<int>) == unsigned(max<int>));
-static_assert(qt_saturate<qint64>(max<int>) == qint64(max<int>));
-
-static_assert(qt_saturate<short>(max<qint64>) == max<short>);
-static_assert(qt_saturate<int>(max<qint64>) == max<int>);
-static_assert(qt_saturate<unsigned>(max<qint64>) == max<unsigned>);
-static_assert(qt_saturate<quint64>(max<qint64>) == quint64(max<qint64>));
-
-static_assert(qt_saturate<short>(max<quint64>) == max<short>);
-static_assert(qt_saturate<int>(max<quint64>) == max<int>);
-static_assert(qt_saturate<unsigned>(max<quint64>) == max<unsigned>);
-static_assert(qt_saturate<qint64>(max<quint64>) == max<qint64>);
-
-static_assert(qt_saturate<short>(min<int>) == min<short>);
-static_assert(qt_saturate<qint64>(min<int>) == qint64(min<int>));
-static_assert(qt_saturate<unsigned>(min<int>) == 0);
-static_assert(qt_saturate<quint64>(min<int>) == 0);
-
-static_assert(qt_saturate<short>(min<qint64>) == min<short>);
-static_assert(qt_saturate<int>(min<qint64>) == min<int>);
-static_assert(qt_saturate<unsigned>(min<qint64>) == 0);
-static_assert(qt_saturate<quint64>(min<qint64>) == 0);
-
-} // namespace QtNumericTests
-
 QT_END_NAMESPACE

src/corelib/global/qnumeric_p.h

@@ -23,6 +23,8 @@
 #include <limits>
 #include <type_traits>
 
+#include <QtCore/q26numeric.h> // temporarily, for saturate_cast
+
 #ifndef __has_extension
 #  define __has_extension(X)    0
 #endif
@@ -431,39 +433,10 @@ template <auto V2, typename T> bool mul_overflow(T v1, T *r)
 }
 #endif // Q_QDOC
 
-/*
-    Safely narrows \a x to \c{To}. Let \c L be
-    \c{std::numeric_limit<To>::min()} and \c H be \c{std::numeric_limit<To>::max()}.
-
-    If \a x is less than L, returns L. If \a x is greater than H,
-    returns H. Otherwise, returns \c{To(x)}.
-*/
 template <typename To, typename From>
 static constexpr auto qt_saturate(From x)
 {
-    static_assert(std::is_integral_v<To>);
-    static_assert(std::is_integral_v<From>);
-
-    [[maybe_unused]]
-    constexpr auto Lo = (std::numeric_limits<To>::min)();
-    constexpr auto Hi = (std::numeric_limits<To>::max)();
-
-    if constexpr (std::is_signed_v<From> == std::is_signed_v<To>) {
-        // same signedness, we can accept regular integer conversion rules
-        return x < Lo  ? Lo :
-               x > Hi  ? Hi :
-               /*else*/  To(x);
-    } else {
-        if constexpr (std::is_signed_v<From>) { // ie. !is_signed_v<To>
-            if (x < From{0})
-                return To{0};
-        }
-
-        // from here on, x >= 0
-        using FromU = std::make_unsigned_t<From>;
-        using ToU = std::make_unsigned_t<To>;
-        return FromU(x) > ToU(Hi) ? Hi : To(x); // assumes Hi >= 0
-    }
+    return q26::saturate_cast<To>(x);
 }
 
 QT_END_NAMESPACE

src/corelib/kernel/qabstracteventdispatcher.cpp

@@ -9,7 +9,8 @@
 #include <private/qthread_p.h>
 #include <private/qcoreapplication_p.h>
 #include <private/qfreelist_p.h>
-#include <private/qnumeric_p.h>
+
+#include <QtCore/q26numeric.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -59,7 +60,7 @@ template <typename T> static T fromDuration(std::chrono::nanoseconds interval)
 {
     using namespace std::chrono;
     qint64 value = ceil<milliseconds>(interval).count();
-    return qt_saturate<T>(value);
+    return q26::saturate_cast<T>(value);
 }
 
 #if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)

src/corelib/kernel/qeventdispatcher_glib.cpp

@@ -4,7 +4,6 @@
 #include "qeventdispatcher_glib_p.h"
 #include "qeventdispatcher_unix_p.h"
 
-#include <private/qnumeric_p.h>
 #include <private/qthread_p.h>
 
 #include "qcoreapplication.h"
@@ -12,6 +11,8 @@
 
 #include <QtCore/qlist.h>
 
+#include <QtCore/q26numeric.h>
+
 #include <glib.h>
 
 using namespace std::chrono;
@@ -104,7 +105,7 @@ static gboolean timerSourcePrepareHelper(GTimerSource *src, gint *timeout)
     }
 
     auto remaining = src->timerList.timerWait().value_or(-1ms);
-    *timeout = qt_saturate<gint>(ceil<milliseconds>(remaining).count());
+    *timeout = q26::saturate_cast<gint>(ceil<milliseconds>(remaining).count());
 
     return (*timeout == 0);
 }

src/corelib/text/qbytearray.cpp

@@ -32,6 +32,7 @@
 #include <stdlib.h>
 
 #include <algorithm>
+#include <QtCore/q26numeric.h>
 
 #ifdef Q_OS_WIN
 #  if !defined(QT_BOOTSTRAPPED) && (defined(QT_NO_CAST_FROM_ASCII) || defined(QT_NO_CAST_FROM_BYTEARRAY))
@@ -728,7 +729,7 @@ QByteArray qCompress(const uchar* data, qsizetype nbytes, int compressionLevel)
     if (out.data() == nullptr) // allocation failed
       return tooMuchData(ZLibOp::Compression);
 
-    qToBigEndian(qt_saturate<CompressSizeHint_t>(nbytes), out.data());
+    qToBigEndian(q26::saturate_cast<CompressSizeHint_t>(nbytes), out.data());
     out.size = HeaderSize;
 
     return xxflate(ZLibOp::Compression, std::move(out), {data, nbytes},

src/corelib/text/qstringconverter.cpp

@@ -25,7 +25,7 @@
 #ifndef QT_BOOTSTRAPPED
 #include <QtCore/qvarlengtharray.h>
 #include <QtCore/q20iterator.h>
-#include <QtCore/private/qnumeric_p.h>
+#include <QtCore/q26numeric.h>
 #endif // !QT_BOOTSTRAPPED
 #endif
 
@@ -1385,12 +1385,12 @@ QString QLocal8Bit::convertToUnicode_sys(QByteArrayView in, quint32 codePage,
 
     // Need it in this scope, since we try to decrease our window size if we
     // encounter an error
-    int nextIn = qt_saturate<int>(mblen);
+    int nextIn = q26::saturate_cast<int>(mblen);
     while (mblen > 0) {
         std::tie(out, outlen) = growOut(1); // Need space for at least one character
         if (!out)
             return {};
-        const int nextOut = qt_saturate<int>(outlen);
+        const int nextOut = q26::saturate_cast<int>(outlen);
         int len = MultiByteToWideChar(codePage, MB_ERR_INVALID_CHARS, mb, nextIn, out, nextOut);
         if (len) {
             mb += nextIn;
@@ -1450,7 +1450,7 @@ QString QLocal8Bit::convertToUnicode_sys(QByteArrayView in, quint32 codePage,
                 break;
             }
         }
-        nextIn = qt_saturate<int>(mblen);
+        nextIn = q26::saturate_cast<int>(mblen);
     }
 
     if (sp.isEmpty()) {
@@ -1572,7 +1572,7 @@ QByteArray QLocal8Bit::convertFromUnicode_sys(QStringView in, quint32 codePage,
     };
 
     const auto getNextWindowSize = [&]() {
-        int nextIn = qt_saturate<int>(uclen);
+        int nextIn = q26::saturate_cast<int>(uclen);
         // The Windows API has some issues if the current window ends in the
         // middle of a surrogate pair, so we avoid that:
         if (nextIn > 1 && QChar::isHighSurrogate(ch[nextIn - 1]))
@@ -1586,7 +1586,7 @@ QByteArray QLocal8Bit::convertFromUnicode_sys(QStringView in, quint32 codePage,
         std::tie(out, outlen) = growOut(1); // We need at least one byte
         if (!out)
             return {};
-        const int nextOut = qt_saturate<int>(outlen);
+        const int nextOut = q26::saturate_cast<int>(outlen);
         len = WideCharToMultiByte(codePage, 0, ch, nextIn, out, nextOut, nullptr, nullptr);
         if (len > 0) {
             ch += nextIn;

src/testlib/qtestresult.cpp

@@ -12,10 +12,9 @@
 #include <QtTest/qtestassert.h>
 #include <QtTest/qtesteventloop.h>
 
-#include <QtCore/private/qnumeric_p.h>
-
 #include <climits>
 #include <cwchar>
+#include <QtCore/q26numeric.h>
 
 #include <stdlib.h>
 #include <stdio.h>
@@ -338,7 +337,7 @@ static int approx_wide_len(const char *s)
     auto r = std::mbsrtowcs(nullptr, &s, INT_MAX, &state);
     if (r == size_t(-1)) // encoding error, fall back to strlen()
         r = strlen(s); // `s` was not advanced since `dst == nullptr`
-    return qt_saturate<int>(r);
+    return q26::saturate_cast<int>(r);
 }
 
 // Overload to format failures for "const char *" - no need to strdup().

tests/auto/corelib/global/qnumeric/tst_qnumeric.cpp

@@ -10,6 +10,8 @@
 #include <math.h>
 #include <float.h>
 
+#include <QtCore/q26numeric.h>
+
 namespace {
     template <typename F> struct Fuzzy {};
     /* Data taken from qglobal.h's implementation of qFuzzyCompare:
@@ -750,5 +752,40 @@ void tst_QNumeric::signedOverflow()
     QCOMPARE(qMulOverflow(maxInt, maxInt, &r), true);
 }
 
+namespace SaturateCastTest {
+
+template <typename T> static constexpr T max = std::numeric_limits<T>::max();
+template <typename T> static constexpr T min = std::numeric_limits<T>::min();
+
+static_assert(q26::saturate_cast<short>(max<unsigned>) == max<short>);
+static_assert(q26::saturate_cast<int>(max<unsigned>) == max<int>);
+static_assert(q26::saturate_cast<qint64>(max<unsigned>) == qint64(max<unsigned>));
+
+static_assert(q26::saturate_cast<short>(max<int>) == max<short>);
+static_assert(q26::saturate_cast<unsigned>(max<int>) == unsigned(max<int>));
+static_assert(q26::saturate_cast<qint64>(max<int>) == qint64(max<int>));
+
+static_assert(q26::saturate_cast<short>(max<qint64>) == max<short>);
+static_assert(q26::saturate_cast<int>(max<qint64>) == max<int>);
+static_assert(q26::saturate_cast<unsigned>(max<qint64>) == max<unsigned>);
+static_assert(q26::saturate_cast<quint64>(max<qint64>) == quint64(max<qint64>));
+
+static_assert(q26::saturate_cast<short>(max<quint64>) == max<short>);
+static_assert(q26::saturate_cast<int>(max<quint64>) == max<int>);
+static_assert(q26::saturate_cast<unsigned>(max<quint64>) == max<unsigned>);
+static_assert(q26::saturate_cast<qint64>(max<quint64>) == max<qint64>);
+
+static_assert(q26::saturate_cast<short>(min<int>) == min<short>);
+static_assert(q26::saturate_cast<qint64>(min<int>) == qint64(min<int>));
+static_assert(q26::saturate_cast<unsigned>(min<int>) == 0);
+static_assert(q26::saturate_cast<quint64>(min<int>) == 0);
+
+static_assert(q26::saturate_cast<short>(min<qint64>) == min<short>);
+static_assert(q26::saturate_cast<int>(min<qint64>) == min<int>);
+static_assert(q26::saturate_cast<unsigned>(min<qint64>) == 0);
+static_assert(q26::saturate_cast<quint64>(min<qint64>) == 0);
+
+} // namespace SaturateCastTest
+
 QTEST_APPLESS_MAIN(tst_QNumeric)
 #include "tst_qnumeric.moc"