CockroachDB has released apd, a new arbitrary-precision decimal package for Go. apd supports normal arithmetic and many elementary functions (ln, sqrt, exp) at any precision. The implementations are based on academic research, making them accurate and fast.
Flags are raised during overflow, rounding, and other conditions, making it possible to safely perform bounded and exact computations. It replaced the underlying implementation of the DECIMAL type in CockroachDB, resulting in much greater accuracy and speed.