Avoid undefined shifts in ceil2 operations

For values where the result cannot be represented the shift width would
be equal to the width of the type, which is undefined. Perform two
well-defined shifts instead of one possible undefined shift.

	* include/bits/hashtable_policy.h (__clp2): Fix calculation for LLP64
	targets where sizeof(size_t) > sizeof(long). Avoid undefined shifts
	of the number of bits in the type.
	* include/std/bit (__ceil2): Avoid undefined shifts.
	* testsuite/26_numerics/bit/bit.pow.two/ceil2.cc: Test values with
	the most signifiant bit set.

From-SVN: r263986

1 files changed, 8 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc b/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc
index 65e1569..e41f82c 100644
--- a/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/bit/bit.pow.two/ceil2.cc
@@ -55,6 +55,14 @@ test(UInt x)
     static_assert( std::ceil2(UInt(3) << 64) == (UInt(4) << 64) );
   }
 
+  constexpr UInt msb = UInt(1) << (std::numeric_limits<UInt>::digits - 1);
+  static_assert( std::ceil2( msb ) == msb );
+  // Larger values cannot be represented so the return value is unspecified,
+  // but must still be valid in constant expressions, i.e. not undefined.
+  static_assert( std::ceil2( UInt(msb + 1) ) != 77 );
+  static_assert( std::ceil2( UInt(msb + 2) ) != 77 );
+  static_assert( std::ceil2( UInt(msb + 77) ) != 77 );
+
   return true;
 }