replacing sub's that can wrap by saturating_sub's
replacing sub's that can wrap by saturating_sub's

graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust