This is an older version of Boost and was released in 2018. The current version is 1.87.0.
C++
03
Added in Boost
1.67.0
Optimized Policy-based Numeric Conversions.
Boost.NumericConversion
The Boost Numeric Conversion library is a collection of tools to describe and perform conversions between values of different numeric types.
The documentation for the library can be found here