Two passes for 128 bit types

Author: mborland

include/boost/decimal/detail/remove_trailing_zeros.hpp

@@ -95,7 +95,9 @@ constexpr auto remove_trailing_zeros(std::uint64_t n) noexcept -> remove_trailin
     return {n, s};
 }
 
-constexpr auto remove_trailing_zeros(uint128 n) noexcept -> remove_trailing_zeros_return<uint128>
+namespace impl {
+
+constexpr auto remove_trailing_zeros_impl(uint128 n) noexcept -> remove_trailing_zeros_return<uint128>
 {
     std::size_t s {};
 
@@ -104,11 +106,6 @@ constexpr auto remove_trailing_zeros(uint128 n) noexcept -> remove_trailing_zero
     s = s * 2U + static_cast<std::size_t>(b);
     n = b ? r : n;
 
-    r = rotr<128>(n * uint128 {UINT64_C(0x3275305C1066), UINT64_C(0xE4A4D1417CD9A041)}, 16);
-    b = r < uint128 {UINT64_C(0x734), UINT64_C(0xACA5F6226F0ADA62)};
-    s = s * 2U + static_cast<std::size_t>(b);
-    n = b ? r : n;
-
     r = rotr<128>(n * uint128 {UINT64_C(0x6B7213EE9F5A78), UINT64_C(0xC767074B22E90E21)}, 8);
     b = r < uint128 {UINT64_C(0x2AF31DC461), UINT64_C(0x1873BF3F70834ACE)};
     s = s * 2U + static_cast<std::size_t>(b);
@@ -132,6 +129,21 @@ constexpr auto remove_trailing_zeros(uint128 n) noexcept -> remove_trailing_zero
     return {n, s};
 }
 
+} // namespace impl
+
+constexpr auto remove_trailing_zeros(uint128 n) noexcept -> remove_trailing_zeros_return<uint128>
+{
+    const auto temp {impl::remove_trailing_zeros_impl(n)};
+    if (BOOST_DECIMAL_LIKELY(temp.number_of_removed_zeros < 31))
+    {
+        return temp;
+    }
+
+    // Since 32 is not a valid value of t we need to keep removing zeros
+    const auto round2 {remove_trailing_zeros(static_cast<std::uint32_t>(temp.trimmed_number))};
+    return {static_cast<uint128>(round2.trimmed_number), round2.number_of_removed_zeros + 31};
+}
+
 } // namespace detail
 } // namespace decimal
 } // namespace boost