Cargo Features

[dependencies]
fpe = { version = "0.6.1", default-features = false, features = ["std", "alloc"] }
default = std

The std feature is set by default whenever fpe is added without default-features = false somewhere in the dependency tree.

std default = alloc
alloc std = num-bigint, num-integer, num-traits

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

num-bigint alloc?
num-integer alloc?
num-traits alloc?