tune explanation of PhantomData ownership annotation

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

diff --git a/src/part08.rs b/src/part08.rs
index 630da427dfec70d2dad9f1920579b2b4277faf8e..7b471b9d827bdb1c6a5d47f836b334a9d9a1b714 100644 (file)
--- a/src/part08.rs
+++ b/src/part08.rs
@@ -20,15 +20,17 @@ fn overflowing_add(a: u64, b: u64, carry: bool) -> (u64, bool) {
     //@ function (see [the documentation](http://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.
     //@ function (see [the documentation](http://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.
     // 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 {
     } 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)                     /*@*/
     }
         // to overflow again, as we are just adding 0 or 1.
         (sum + if carry { 1 } else { 0 }, true)                     /*@*/
     }


@@ -82,7 +84,10 @@ impl ops::Add<BigInt> for BigInt {
             carry = new_carry;                                                  /*@*/
         }
         // **Exercise 08.2**: Handle the final `carry`, and return the sum.
             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 }                                             /*@@*/

     }
 }
 
     }
 }
 


@@ -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 {
 //@ 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]);
     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`.
 
 // **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) | [next](part09.html)