X-Git-Url: https://git.ralfj.de/rust-101.git/blobdiff_plain/ee5a849f625d3bd9bd9bb661428d1c051f285ebe..a0ae4ec8a5da0e171cb2d2f68621fa98f5ea610b:/src/part08.rs
diff --git a/src/part08.rs b/src/part08.rs
index cacff46..c18cbeb 100644
--- a/src/part08.rs
+++ b/src/part08.rs
@@ -17,18 +17,20 @@ fn overflowing_add(a: u64, b: u64, carry: bool) -> (u64, bool) {
//@ The reason for this is that many serious security vulnerabilities have been caused by integer overflows, so just assuming
//@ "per default" that they are intended is dangerous.
//@ If you explicitly *do* want an overflow to happen, you can call the `wrapping_add`
- //@ function (see [the documentation](http://doc.rust-lang.org/stable/std/primitive.u64.html#method.wrapping_add),
+ //@ function (see [the documentation](https://doc.rust-lang.org/stable/std/primitive.u64.html#method.wrapping_add),
//@ there are similar functions for other arithmetic operations). There are also similar functions
//@ `checked_add` etc. to enforce the overflow check.
- let sum = u64::wrapping_add(a, b);
+ let sum = a.wrapping_add(b);
// If an overflow happened, then the sum will be smaller than *both* summands. Without an overflow, of course, it will be
// at least as large as both of them. So, let's just pick one and check.
if sum >= a {
// The addition did not overflow.
// **Exercise 08.1**: Write the code to handle adding the carry in this case.
- unimplemented!()
+ let sum_total = sum.wrapping_add(if carry { 1 } else { 0 });/*@@*/
+ let had_overflow = sum_total < sum; /*@@*/
+ (sum_total, had_overflow) /*@@*/
} else {
- // The addition *did* overflow. It is impossible for the addition of the carry
+ // Otherwise, the addition *did* overflow. It is impossible for the addition of the carry
// to overflow again, as we are just adding 0 or 1.
(sum + if carry { 1 } else { 0 }, true) /*@*/
}
@@ -55,7 +57,7 @@ fn test_overflowing_add() {
impl ops::Add for BigInt {
//@ Besides static functions and methods, traits can contain *associated types*: This is a type chosen by every particular implementation
//@ of the trait. The methods of the trait can then refer to that type. In the case of addition, it is used to give the type of the result.
- //@ (Also see the [documentation of `Add`](http://doc.rust-lang.org/stable/std/ops/trait.Add.html).)
+ //@ (Also see the [documentation of `Add`](https://doc.rust-lang.org/stable/std/ops/trait.Add.html).)
//@
//@ In general, you can consider the two `BigInt` given above (in the `impl` line) *input* types of trait search: When
//@ `a + b` is invoked with `a` having type `T` and `b` having type `U`, Rust tries to find an implementation of `Add` for
@@ -82,17 +84,20 @@ impl ops::Add for BigInt {
carry = new_carry; /*@*/
}
// **Exercise 08.2**: Handle the final `carry`, and return the sum.
- unimplemented!()
+ if carry { /*@@*/
+ result_vec.push(1); /*@@*/
+ } /*@@*/
+ BigInt { data: result_vec } /*@@*/
}
}
-// ## Traits and borrowed types
+// ## Traits and reference types
//@ If you inspect the addition function above closely, you will notice that it actually consumes ownership of both operands
//@ to produce the result. This is, of course, in general not what we want. We'd rather like to be able to add two `&BigInt`.
// Writing this out becomes a bit tedious, because trait implementations (unlike functions) require full explicit annotation
// of lifetimes. Make sure you understand exactly what the following definition says. Notice that we can implement a trait for
-// a borrowed type!
+// a reference type!
impl<'a, 'b> ops::Add<&'a BigInt> for &'b BigInt {
type Output = BigInt;
fn add(self, rhs: &'a BigInt) -> Self::Output {
@@ -101,6 +106,8 @@ impl<'a, 'b> ops::Add<&'a BigInt> for &'b BigInt {
}
}
+// **Exercise 08.4**: Implement the two missing combinations of arguments for `Add`. You should not have to duplicate the implementation.
+
// ## Modules
//@ As you learned, tests can be written right in the middle of your development in Rust. However, it is
//@ considered good style to bundle all tests together. This is particularly useful in cases where
@@ -111,13 +118,15 @@ impl<'a, 'b> ops::Add<&'a BigInt> for &'b BigInt {
//@ Rust would not bother compiling them when you just build your program for normal use. Other than that, tests work as usually.
#[cfg(test)]
mod tests {
- #[test]
+ use part05::BigInt;
+
+ /*#[test]*/
fn test_add() {
let b1 = BigInt::new(1 << 32);
let b2 = BigInt::from_vec(vec![0, 1]);
assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1]));
- // **Exercise 08.4**: Add some more cases to this test.
+ // **Exercise 08.5**: Add some more cases to this test.
}
}
//@ As already mentioned, outside of the module, only those items declared public with `pub` may be used. Submodules can access
@@ -140,7 +149,7 @@ mod tests {
//@ from other files. This ensures that the directory structure mirrors the structure of the modules, with `mod.rs`, `lib.rs`
//@ and `main.rs` representing a directory or crate itself (similar to, e.g., `__init__.py` in Python).
-// **Exercise 08.4**: Write a subtraction function, and testcases for it. Decide for yourself how you want to handle negative results.
+// **Exercise 08.6**: Write a subtraction function, and testcases for it. Decide for yourself how you want to handle negative results.
// For example, you may want to return an `Option`, to panic, or to return `0`.
-//@ [index](main.html) | [previous](part07.html) | [next](main.html)
+//@ [index](main.html) | [previous](part07.html) | [raw source](workspace/src/part08.rs) | [next](part09.html)