Some of the Decimal128 math functions are non-commutative and have a possibly confusing interface:

a.logarithm(b)

This would calculate the logarithm of "a", with base "b". Confusion has led to bugs in the past such as SERVER-91223. A more clear interface would use static methods, like:

Decimal128::logarithm(a, b)

or even with comments

Decimal128::logarithm(a /*input*/, b  /*base*/)

This is especially important for non-commutative functions.