This is probably a $y=f(x)$ question, but I searched several times on the MathOverflow without success so I decided to explicitly ask for the help of other members: please feel free to ask me to remove the question if inappropriate.

Nearly a month or so, in a MathOverflow answer (I guess so, but at this point I should consider the possibility I am wrong) to a question on (computational) number theory I read about a C library for arbitrary precision arithmetic which was successfully used in several research papers, including one where the Authors proved the existence of a soliton solution to a PDE by proving the strict positivity of a term by estimating its size as being not less than a $21$ bit mantissa multiplied by $10^{-5000}$ (I am fairly sure of this fact but, as already said, I should consider the possibility I am wrong). I went to the library web page and saved the link in my bookmarks: then a crash occurred (yes, also experienced electronics engineers lose data...) and up until now I was not able to find the former Q&A.

**Question**: can someone provide me a reference to this library?

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