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Fix tst_qmath when compiled with C++20

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On several platforms std::bit_ceil() returns 1 for input values that
would overflow the output. Our test expects 0 though. Since the value
is documented as undefined, avoid it.

Pick-to: 6.3 6.2
Change-Id: I00556893a8f0e1e24f08f73cd112b56148bc5bd0
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
This commit is contained in:
Allan Sandfeld Jensen 2022-02-05 14:32:05 +01:00
parent 4082fe8a39
commit ace9764c99
1 changed files with 4 additions and 0 deletions
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4
src/corelib/kernel/qmath.h
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@ -371,6 +371,8 @@ constexpr inline quint64 qConstexprNextPowerOfTwo(qint64 v)
constexpr inline quint32 qNextPowerOfTwo(quint32 v) constexpr inline quint32 qNextPowerOfTwo(quint32 v)
{ {
#if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L #if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L
if (static_cast<qint32>(v) < 0)
return 0; // std::bit_ceil() is undefined for values that would overflow, but we document them to be 0
return std::bit_ceil(v + 1); return std::bit_ceil(v + 1);
#elif defined(QT_HAS_BUILTIN_CLZ) #elif defined(QT_HAS_BUILTIN_CLZ)
if (v == 0) if (v == 0)
@ -384,6 +386,8 @@ constexpr inline quint32 qNextPowerOfTwo(quint32 v)
constexpr inline quint64 qNextPowerOfTwo(quint64 v) constexpr inline quint64 qNextPowerOfTwo(quint64 v)
{ {
#if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L #if defined(__cpp_lib_int_pow2) && __cpp_lib_int_pow2 >= 202002L
if (static_cast<qint64>(v) < 0)
return 0; // std::bit_ceil() is undefined for values that would overflow, but we document them to be 0
return std::bit_ceil(v + 1); return std::bit_ceil(v + 1);
#elif defined(QT_HAS_BUILTIN_CLZLL) #elif defined(QT_HAS_BUILTIN_CLZLL)
if (v == 0) if (v == 0)