Merging r313776:

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r313776 | marshall | 2017-09-20 10:34:11 -0700 (Wed, 20 Sep 2017) | 1 line

Fix a bit of UB in __independent_bits_engine. Fixes PR#34663
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git-svn-id: https://llvm.org/svn/llvm-project/libcxx/branches/release_50@318236 91177308-0d34-0410-b5e6-96231b3b80d8

include/algorithm

@@ -3013,6 +3013,7 @@ template<class _Engine, class _UIntType>
 _UIntType
 __independent_bits_engine<_Engine, _UIntType>::__eval(true_type)
 {
+    const size_t _WRt = numeric_limits<result_type>::digits;
     result_type _Sp = 0;
     for (size_t __k = 0; __k < __n0_; ++__k)
     {
@@ -3021,7 +3022,7 @@ __independent_bits_engine<_Engine, _UIntType>::__eval(true_type)
         {
             __u = __e_() - _Engine::min();
         } while (__u >= __y0_);
-        if (__w0_ < _WDt)
+        if (__w0_ < _WRt)
             _Sp <<= __w0_;
         else
             _Sp = 0;
@@ -3034,7 +3035,7 @@ __independent_bits_engine<_Engine, _UIntType>::__eval(true_type)
         {
             __u = __e_() - _Engine::min();
         } while (__u >= __y1_);
-        if (__w0_ < _WDt - 1)
+        if (__w0_ < _WRt - 1)
             _Sp <<= __w0_ + 1;
         else
             _Sp = 0;