type usage fix.

Author: IRainman

include/fast_float/decimal_to_binary.h

@@ -141,8 +141,9 @@ compute_float(am_pow_t q, am_mant_t w) noexcept {
   // branchless approach: value128 product = compute_product(q, w); but in
   // practice, we can win big with the compute_product_approximation if its
   // additional branch is easily predicted. Which is best is data specific.
-  am_bits_t const upperbit = static_cast<am_bits_t>(product.high >> 63);
-  am_bits_t const shift = upperbit + 64 - binary::mantissa_explicit_bits() - 3;
+  auto const upperbit = static_cast<am_bits_t>(product.high >> 63);
+  auto const shift = static_cast<am_bits_t>(
+      upperbit + 64 - binary::mantissa_explicit_bits() - 3);
 
   // Shift right the mantissa to the correct position
   answer.mantissa = product.high >> shift;