qNextPowerOfTwo: rewrite using the newly added q20::bit_ceil()

Change-Id: I6f6d8110327d1ba7d519fffd0aa2e18d87477e56
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

src/corelib/kernel/qmath.h

@@ -288,67 +288,16 @@ constexpr inline long double qRadiansToDegrees(long double radians)
 // questionable that someone is manipulating quantities in radians
 // using integral datatypes...
 
-namespace QtPrivate {
-constexpr inline quint32 qConstexprNextPowerOfTwo(quint32 v)
-{
-    v |= v >> 1;
-    v |= v >> 2;
-    v |= v >> 4;
-    v |= v >> 8;
-    v |= v >> 16;
-    ++v;
-    return v;
-}
-
-constexpr inline quint64 qConstexprNextPowerOfTwo(quint64 v)
-{
-    v |= v >> 1;
-    v |= v >> 2;
-    v |= v >> 4;
-    v |= v >> 8;
-    v |= v >> 16;
-    v |= v >> 32;
-    ++v;
-    return v;
-}
-
-constexpr inline quint32 qConstexprNextPowerOfTwo(qint32 v)
-{
-    return qConstexprNextPowerOfTwo(quint32(v));
-}
-
-constexpr inline quint64 qConstexprNextPowerOfTwo(qint64 v)
-{
-    return qConstexprNextPowerOfTwo(quint64(v));
-}
-} // namespace QtPrivate
-
 constexpr inline quint32 qNextPowerOfTwo(quint32 v)
 {
     Q_ASSERT(static_cast<qint32>(v) >= 0); // There is a next power of two
-#if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L
+    return q20::bit_ceil(v + 1);
-    return std::bit_ceil(v + 1);
-#elif defined(QT_HAS_BUILTIN_CLZ)
-    if (v == 0)
-        return 1;
-    return 2U << (31 ^ QAlgorithmsPrivate::qt_builtin_clz(v));
-#else
-    return QtPrivate::qConstexprNextPowerOfTwo(v);
-#endif
 }
 
 constexpr inline quint64 qNextPowerOfTwo(quint64 v)
 {
     Q_ASSERT(static_cast<qint64>(v) >= 0); // There is a next power of two
-#if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L
+    return q20::bit_ceil(v + 1);
-    return std::bit_ceil(v + 1);
-#elif defined(QT_HAS_BUILTIN_CLZLL)
-    if (v == 0)
-        return 1;
-    return Q_UINT64_C(2) << (63 ^ QAlgorithmsPrivate::qt_builtin_clzll(v));
-#else
-    return QtPrivate::qConstexprNextPowerOfTwo(v);
-#endif
 }
 
 constexpr inline quint32 qNextPowerOfTwo(qint32 v)

src/corelib/tools/qtaggedpointer.h

@@ -25,7 +25,7 @@ namespace QtPrivate {
         static_assert(tagBits > 0,
             "Alignment of template parameter does not allow any tags");
 
-        static constexpr size_t tagSize = QtPrivate::qConstexprNextPowerOfTwo(nextByteSize(tagBits));
+        static constexpr size_t tagSize = qNextPowerOfTwo(nextByteSize(tagBits));
         static_assert(tagSize < sizeof(quintptr),
             "Alignment of template parameter allows tags masking away pointer");
 

tests/auto/corelib/kernel/qmath/tst_qmath.cpp

@@ -6,6 +6,8 @@
 #include <qmath.h>
 #include <qfloat16.h>
 
+#include <q20bit.h>
+
 class tst_QMath : public QObject
 {
     Q_OBJECT
@@ -294,6 +296,12 @@ void tst_QMath::qNextPowerOfTwo32U_data()
 
 void tst_QMath::qNextPowerOfTwo32U()
 {
+    // confirm constexprness
+    static_assert(q20::bit_ceil(0U) == 1);
+    static_assert(q20::bit_ceil(1U) == 1);
+    static_assert(q20::bit_ceil(2U) == 2);
+    static_assert(q20::bit_ceil(3U) == 4);
+    static_assert(q20::bit_ceil(0x7fff'ffffU) == 0x8000'0000U);
     QFETCH(quint32, input);
     QFETCH(quint32, output);
 
@@ -343,6 +351,13 @@ void tst_QMath::qNextPowerOfTwo64U_data()
 
 void tst_QMath::qNextPowerOfTwo64U()
 {
+    static_assert(q20::bit_ceil(Q_UINT64_C(0)) == 1);
+    static_assert(q20::bit_ceil(Q_UINT64_C(1)) == 1);
+    static_assert(q20::bit_ceil(Q_UINT64_C(2)) == 2);
+    static_assert(q20::bit_ceil(Q_UINT64_C(3)) == 4);
+    static_assert(q20::bit_ceil(quint64(~0U)) == Q_UINT64_C(0x1'0000'0000));
+    static_assert(q20::bit_ceil(Q_UINT64_C(0x7FFFFFFFFFFFFFFF))
+                  == Q_UINT64_C(0x8000000000000000));
     QFETCH(quint64, input);
     QFETCH(quint64, output);