Fix possible promotion issues for ancient clang toolchains

Author: mborland

include/boost/decimal/decimal32_fast.hpp

@@ -379,7 +379,7 @@ constexpr decimal32_fast::decimal32_fast(T1 coeff, T2 exp, bool sign) noexcept
         exp = 0;
     }
 
-    auto biased_exp {static_cast<std::uint64_t>(exp + detail::bias)};
+    auto biased_exp {static_cast<std::int64_t>(exp + detail::bias)};
 
     // Decimal32 exponent holds 8 bits
     if (biased_exp > detail::max_biased_exp_v<decimal32_fast> || exp > detail::max_biased_exp_v<decimal32_fast>)
@@ -1028,7 +1028,7 @@ constexpr auto div_impl(decimal32_fast lhs, decimal32_fast rhs, decimal32_fast&
               << "\nexp rhs: " << exp_rhs << std::endl;
     #endif
 
-    using promoted_type = std::uint_fast64_t;
+    using promoted_type = std::uint64_t;
 
     // We promote to uint64 since the significands are currently 32-bits
     // By appending enough zeros to the LHS we end up finding what we need anyway

include/boost/decimal/detail/promote_significand.hpp

@@ -19,7 +19,7 @@ namespace impl {
 template <BOOST_DECIMAL_DECIMAL_FLOATING_TYPE DecimalType, BOOST_DECIMAL_INTEGRAL Integer>
 struct promote_significand
 {
-    using type = std::conditional_t<std::numeric_limits<Integer>::digits10 < std::numeric_limits<typename DecimalType::significand_type>::digits10,
+    using type = std::conditional_t<std::numeric_limits<make_unsigned_t<Integer>>::digits10 < std::numeric_limits<typename DecimalType::significand_type>::digits10,
                                     typename DecimalType::significand_type, detail::make_unsigned_t<Integer>>;
 };