Fixed addition with operands of different sizes

When two numbers (i.e. their _operands list) had different sizes, their
addition was resulting in undefined behaviour because, at some point in
the computation, we were dereferencing the iterator of the shortest
number (and the iterator was _operands.cend()).

Fixed by virtually "padding" the shortest number with zeros.

Signed-off-by: Olivier Gayot <og@satcom1.com>

1 files changed, 3 insertions, 11 deletions

diff --git a/number.cpp b/number.cpp
index ae4b167..d16f37f 100644
--- a/number.cpp
+++ b/number.cpp
@@ -67,11 +67,6 @@ number::to_uint32() const
 number
 number::operator+(const number &n) const
 {
-    /* We make sure our object is greater than or equal to n. */
-    if (*this < n) {
-        return n.operator+(*this);
-    }
-
     number result;
 
     auto it = _operands.cbegin();
@@ -79,9 +74,9 @@ number::operator+(const number &n) const
 
     bool carry = false;
 
-    while (it != _operands.cend()) {
-        const auto n1 = *it;
-        const auto n2 = *it_n;
+    while (it != _operands.cend() || it_n != n._operands.cend()) {
+        const auto n1 = (it != _operands.cend()) ? *it++ : 0;
+        const auto n2 = (it_n != n._operands.cend()) ? *it_n++ : 0;
 
         result._operands.push_back(n1 + n2 + (carry ? 1 : 0));
 
@@ -90,9 +85,6 @@ number::operator+(const number &n) const
         } else {
             carry = ((UINT32_MAX - n1 - (carry ? 1 : 0)) < n2);
         }
-
-        ++it;
-        ++it_n;
     }
 
     if (carry) {