Fix calculation of resultant digits

mborland · mborland · commit 35ada3d6044e · 2025-01-21T14:09:21.000-05:00
diff --git a/include/boost/decimal/detail/mul_impl.hpp b/include/boost/decimal/detail/mul_impl.hpp
@@ -125,7 +125,7 @@ constexpr auto d128_mul_impl(T1 lhs_sig, U1 lhs_exp, bool lhs_sign,
     const auto rhs_dig {detail::num_digits(rhs_sig)};
 
     // If we can avoid it don't do 256 bit multiplication because it is slow
-    if (lhs_dig * rhs_dig <= std::numeric_limits<uint128>::digits10)
+    if (lhs_dig + rhs_dig <= std::numeric_limits<uint128>::digits10)
     {
         auto res_sig {lhs_sig * rhs_sig};
         auto res_exp {lhs_exp + rhs_exp};

Original file line number	Diff line number	Diff line change
`@@ -125,7 +125,7 @@ constexpr auto d128_mul_impl(T1 lhs_sig, U1 lhs_exp, bool lhs_sign,`
`125`	`125`	`const auto rhs_dig {detail::num_digits(rhs_sig)};`
`126`	`126`
`127`	`127`	`// If we can avoid it don't do 256 bit multiplication because it is slow`
`128`		`- if (lhs_dig * rhs_dig <= std::numeric_limits<uint128>::digits10)`
	`128`	`+ if (lhs_dig + rhs_dig <= std::numeric_limits<uint128>::digits10)`
`129`	`129`	`{`
`130`	`130`	`auto res_sig {lhs_sig * rhs_sig};`
`131`	`131`	`auto res_exp {lhs_exp + rhs_exp};`