Added usage of std::countr_zero, std::countl_zero

When C++20 is available. Copied from VMA.

Author: adam-sawicki-a

src/D3D12MemAlloc.cpp

@@ -49,6 +49,14 @@
 ////////////////////////////////////////////////////////////////////////////////
 #ifndef _D3D12MA_CONFIGURATION
 
+#if !defined(D3D12MA_CPP20)
+ #if __cplusplus >= 202002L || _MSVC_LANG >= 202002L // C++20
+ #define D3D12MA_CPP20 1
+ #else
+ #define D3D12MA_CPP20 0
+ #endif
+#endif
+
 #ifdef _WIN32
  #if !defined(WINVER) || WINVER < 0x0600
  #error Required at least WinAPI version supporting: client = Windows Vista, server = Windows Server 2008.
@@ -71,6 +79,10 @@
  #define D3D12MA_ASSERT(cond) assert(cond)
 #endif
 
+#if D3D12MA_CPP20
+ #include <bit>
+#endif
+
 // Assert that will be called very often, like inside data structures e.g. operator[].
 // Making it non-empty can make program slow.
 #ifndef D3D12MA_HEAVY_ASSERT
@@ -303,6 +315,10 @@ static UINT8 BitScanLSB(UINT64 mask)
  if (_BitScanForward64(&pos, mask))
  return static_cast<UINT8>(pos);
  return UINT8_MAX;
+#elif D3D12MA_CPP20
+ if (mask != 0)
+ return static_cast<uint8_t>(std::countr_zero(mask));
+ return UINT8_MAX;
 #elif defined __GNUC__ || defined __clang__
  return static_cast<UINT8>(__builtin_ffsll(mask)) - 1U;
 #else
@@ -325,6 +341,10 @@ static UINT8 BitScanLSB(UINT32 mask)
  if (_BitScanForward(&pos, mask))
  return static_cast<UINT8>(pos);
  return UINT8_MAX;
+#elif D3D12MA_CPP20
+ if (mask != 0)
+ return static_cast<uint8_t>(std::countr_zero(mask));
+ return UINT8_MAX;
 #elif defined __GNUC__ || defined __clang__
  return static_cast<UINT8>(__builtin_ffs(mask)) - 1U;
 #else
@@ -347,6 +367,9 @@ static UINT8 BitScanMSB(UINT64 mask)
  unsigned long pos;
  if (_BitScanReverse64(&pos, mask))
  return static_cast<UINT8>(pos);
+#elif D3D12MA_CPP20
+ if (mask != 0)
+ return 63 - static_cast<uint8_t>(std::countl_zero(mask));
 #elif defined __GNUC__ || defined __clang__
  if (mask)
  return 63 - static_cast<UINT8>(__builtin_clzll(mask));
@@ -369,6 +392,9 @@ static UINT8 BitScanMSB(UINT32 mask)
  unsigned long pos;
  if (_BitScanReverse(&pos, mask))
  return static_cast<UINT8>(pos);
+#elif D3D12MA_CPP20
+ if (mask != 0)
+ return 31 - static_cast<uint8_t>(std::countl_zero(mask));
 #elif defined __GNUC__ || defined __clang__
  if (mask)
  return 31 - static_cast<UINT8>(__builtin_clz(mask));