implement add and sub for height
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@ -1,5 +1,7 @@
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use crate::serialization::SerializationError;
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use std::ops::{Add, Sub};
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/// The height of a block is the length of the chain back to the genesis block.
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///
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/// # Invariants
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@ -41,6 +43,54 @@ impl Height {
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pub const MAX_AS_U32: u32 = Self::MAX.0;
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}
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// Block heights live in a torsor, they can only be contructed but not computed directly.
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// Addition and substraction is done in the underlying types(u32) and not in the heights themselves.
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// This u32 numbers are a group and they can be added and substracted normally to get a new integer.
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// Having the result of the computation the `Height(X)` constructor can be used to build a new `Height`.
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// N = Height1.U - Height2.U
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// Given two `Height`s use the underlying value of them to compute the difference,
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// return this number as it is.
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impl Sub<Height> for Height {
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type Output = Option<u32>;
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fn sub(self, rhs: Height) -> Option<u32> {
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self.0.checked_sub(rhs.0)
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}
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}
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// H = Height(Height.U + N)
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// Given a `Height` and a number, sum the underlying value to the number,
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// with the result construct a new `Height` and return it.
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impl Add<u32> for Height {
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type Output = Option<Height>;
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fn add(self, rhs: u32) -> Option<Height> {
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let result = self.0.checked_add(rhs);
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match result {
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Some(h) if (Height(h) <= Height::MAX) => Some(Height(h)),
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Some(_) => None,
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None => None,
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}
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}
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}
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// H = Height(Height.U - N)
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// Given a `Height` and a number, substract the number to the underlying value,
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// with the result construct a new `Height` and return it.
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impl Sub<u32> for Height {
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type Output = Option<Height>;
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fn sub(self, rhs: u32) -> Option<Height> {
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let result = self.0.checked_sub(rhs);
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match result {
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Some(h) if (Height(h) >= Height::MIN) => Some(Height(h)),
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Some(_) => None,
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None => None,
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}
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}
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}
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#[cfg(test)]
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use proptest::prelude::*;
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#[cfg(test)]
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@ -53,3 +103,17 @@ impl Arbitrary for Height {
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type Strategy = BoxedStrategy<Self>;
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}
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#[test]
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fn operator_tests() {
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assert_eq!(Some(Height(2)), Height(1) + 1);
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assert_eq!(None, Height::MAX + 1);
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assert_eq!(Some(Height(1)), Height(2) - 1);
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assert_eq!(Some(Height(0)), Height(1) - 1);
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assert_eq!(None, Height(0) - 1);
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assert_eq!(Some(1), Height(2) - Height(1));
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assert_eq!(Some(0), Height(1) - Height(1));
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assert_eq!(None, Height(0) - Height(1));
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}
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