256 bit integer types.

Cargo.toml

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+[package]
+name = "pathfinder2"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

src/main.rs

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+mod u256;
+
+fn main() {
+    println!("Hello, world!");
+}

src/u256.rs

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+use std::fmt::Display;
+use std::fmt::Formatter;
+use std::ops::{Add, AddAssign};
+
+#[derive(Clone, Copy, Debug, Default, Hash, PartialEq, PartialOrd)]
+pub struct U256([u128; 2]);
+
+impl U256 {}
+
+impl From<u128> for U256 {
+    fn from(item: u128) -> Self {
+        U256([0, item])
+    }
+}
+
+// TODO str is using unicode stuff - maybe we should use Vec<u8> for efficiency reasons?
+impl From<&str> for U256 {
+    fn from(item: &str) -> Self {
+        if item.starts_with("0x") {
+            let len = item.len();
+            assert!(len <= 2 + 32 + 32, "{}", len);
+            let low_start = if len >= 2 + 32 { len - 32 } else { 2 };
+            let low_hex = &item[low_start..];
+            // disallow + and - prefixes
+            assert!(
+                low_hex.as_bytes().get(0) != Some(&54) && low_hex.as_bytes().get(0) != Some(&43)
+            );
+            let low = if low_hex.is_empty() { 0 } else {u128::from_str_radix(low_hex, 16).unwrap()};
+            let high_start = if len >= 2 + 32 + 32 { len - 64 } else { 2 };
+            let high_hex = &item[high_start..low_start];
+            // disallow + and - prefixes
+            assert!(
+                high_hex.as_bytes().get(0) != Some(&54) && high_hex.as_bytes().get(0) != Some(&43)
+            );
+            let high = if high_hex.is_empty() { 0 } else { u128::from_str_radix(high_hex, 16).unwrap() };
+            U256([high, low])
+        } else {
+            todo!("Decimal import");
+        }
+    }
+}
+
+impl Add for U256 {
+    type Output = Self;
+    fn add(self, rhs: Self) -> Self {
+        let (low, carry) = self.0[1].overflowing_add(rhs.0[1]);
+        let (mut high, mut overflow) = self.0[0].overflowing_add(rhs.0[0]);
+        assert!(!overflow);
+        if carry {
+            (high, overflow) = high.overflowing_add(1);
+            assert!(!overflow);
+        }
+        Self([high, low])
+    }
+}
+
+impl AddAssign for U256 {
+    fn add_assign(&mut self, rhs: U256) {
+        *self = *self + rhs;
+    }
+}
+
+impl Display for U256 {
+    fn fmt(&self, f: &mut Formatter) -> std::fmt::Result {
+        if self.0[0] == 0 {
+            write!(f, "{:#x}", self.0[1])
+        } else {
+            write!(f, "{:#x}{:032x}", self.0[0], self.0[1])
+        }
+    }
+}
+
+mod test {
+    use super::*;
+    #[test]
+    fn to_string() {
+        assert_eq!(format!("{}", U256::from(0)), "0x0");
+        assert_eq!(
+            format!("{}", U256::from(u128::MAX)),
+            "0xffffffffffffffffffffffffffffffff"
+        );
+    }
+
+    #[test]
+    fn add() {
+        assert_eq!(
+            format!("{}", U256::from(u128::MAX) + U256::from(u128::MAX)),
+            "0x1fffffffffffffffffffffffffffffffe"
+        );
+        let mut x = U256::from(u128::MAX);
+        x += U256::from(1);
+        assert_eq!(format!("{x}"), "0x100000000000000000000000000000000");
+    }
+
+    #[test]
+    fn compare() {
+        assert!(U256::from(0) < U256::from(1));
+        assert!(U256::from("0x100000000000000000000000000000000") > U256::from(1));
+    }
+
+    #[test]
+    fn from_hex() {
+        assert_eq!(U256::from("0x"), U256::from(0));
+        assert_eq!(U256::from("0x1"), U256::from(1));
+        assert_eq!(U256::from("0x01"), U256::from(1));
+        assert_eq!(
+            U256::from("0x1fffffffffffffffffffffffffffffffe"),
+            U256::from(u128::MAX) + U256::from(u128::MAX)
+        );
+        assert_eq!(
+            U256::from("0x001fffffffffffffffffffffffffffffffe"),
+            U256::from(u128::MAX) + U256::from(u128::MAX)
+        );
+        assert_eq!(
+            U256::from("0x100000000000000000000000000000000"),
+            U256::from(u128::MAX) + U256::from(1)
+        );
+    }
+
+}