Trim trailing zeros for dec128_fast mul

Author: mborland

include/boost/decimal/decimal128_fast.hpp

@@ -909,9 +909,21 @@ constexpr auto operator*(decimal128_fast lhs, decimal128_fast rhs) noexcept -> d
     }
     #endif
 
-    return detail::d128_fast_mul_impl<decimal128_fast>(
-            lhs.significand_, lhs.biased_exponent(), lhs.sign_,
-            rhs.significand_, rhs.biased_exponent(), rhs.sign_);
+    auto lhs_sig {lhs.full_significand()};
+    auto lhs_exp {lhs.biased_exponent()};
+    const auto lhs_zeros {detail::remove_trailing_zeros(lhs_sig)};
+    lhs_sig = lhs_zeros.trimmed_number;
+    lhs_exp += static_cast<std::int32_t>(lhs_zeros.number_of_removed_zeros);
+
+    auto rhs_sig {rhs.full_significand()};
+    auto rhs_exp {rhs.biased_exponent()};
+    const auto rhs_zeros {detail::remove_trailing_zeros(rhs_sig)};
+    rhs_sig = rhs_zeros.trimmed_number;
+    rhs_exp += static_cast<std::int32_t>(rhs_zeros.number_of_removed_zeros);
+
+    return detail::d128_mul_impl<decimal128_fast>(
+            lhs_sig, lhs_exp, lhs.sign_,
+            rhs_sig, rhs_exp, rhs.sign_);
 }
 
 template <typename Integer>