VIP: epsilon(decimal) builtin for decimal types

[charles-cooper]

Simple Summary

Add an epsilon() builtin which returns the smallest non-zero value for a decimal type.

Motivation

Similar to #1923, it is nice to not have to type out these special constants (as is done for instance here: https://github.com/vyperlang/vyper/pull/2935/files#diff-86a0306fe1e101309bd0992f2780ec4f0c3dd319940131270904157845c9d9beR79)

Specification

Add an epsilon() builtin which takes a decimal typedef as its argument, and returns the smallest non-zero value for that type. Currently as we only have one decimal type, this would be epsilon(decimal) == 1e-10. In general as we add more decimal types, epsilon(Decimal[N, ...]) would return 1 / 10**N. This is already in the typeinfo for decimals, it's just a matter of exposing as a builtin

vyper/vyper/codegen/types/types.py

Lines 110 to 112 in 9a02a44

	@property
	def epsilon(self) -> Decimal:
	return 1 / Decimal(self.divisor)

Copyright

Copyright and related rights waived via CC0

[charles-cooper]

note: consider for future VIP to expose a scale(decimal) builtin which returns 1 / epsilon(decimal). This could be useful for instance for scaling raw integers for manual implementations of fixed point math.

[charles-cooper]

meeting notes: approved