37a4c70bd4
When the signs differ, the precision of the conversion sometimes drops below 106 bits. This strategy is identical to the hexadecimal variant. I've refactored tst-sprintf3 to enable testing a value with more than 30 significant digits in order to demonstrate this failure and its solution. Additionally, this implicitly fixes a typo in the shift quantities when subtracting from the high mantissa to compute the difference.