add a README explaining the purpose of the workspace/ folder

[rust-101.git] / src / part08.rs

diff --git a/src/part08.rs b/src/part08.rs
index feb2abc5a36f7bbee3f81f831ff9499476d27611..340de24a88e071f2e2ab68fd54ee646b85fd7e04 100644 (file)
--- a/src/part08.rs
+++ b/src/part08.rs
@@ -17,16 +17,18 @@ 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. <br/>
     //@ 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. <br/>
         // **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 {
         // 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.
@@ -55,7 +57,7 @@ fn test_overflowing_add() {
 impl ops::Add<BigInt> 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<BigInt> 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 {
@@ -113,7 +118,9 @@ 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]);
@@ -145,4 +152,4 @@ mod tests {
 // **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](part09.html)
+//@ [index](main.html) | [previous](part07.html) | [raw source](https://www.ralfj.de/git/rust-101.git/blob_plain/HEAD:/workspace/src/part08.rs) | [next](part09.html)