Hector McGillivray

In addition to Rudy's BigNumbers Library previously mentioned by DelphiUdIT, there is the high-precision float library Neslib.MultiPrecision on GitHub which is likely to give you the precision required while retaining better performance. More information here on the implementation and algorithms used.

I have suffered from this, as a customer, more than once. Complete rewrites, for behind-the-scenes benefits (often of dubious merits to the company, and of no benefit to the customer) that remove critical features essential to operations. I have submitted bug reports on missing features that have had responses like "We didn't think anybody used that" and even "We didn't know that it did that". The amount of use-case knowledge that gets lost in a total rewrite should never be underestimated.