abacus: bignum: add output operator

src/bignum/bignum.cc

@@ -1,6 +1,8 @@
 #include "bignum.hh"
 
 #include <algorithm>
+#include <iostream>
+#include <iterator>
 
 #include <cassert>
 #include <cmath>
@@ -27,6 +29,20 @@ BigNum::BigNum(std::int64_t number) {
     assert(is_canonicalized());
 }
 
+std::ostream& BigNum::dump(std::ostream& out) const {
+    if (sign_ == 0) {
+        return out << '0';
+    }
+
+    if (sign_ < 0) {
+        out << '-';
+    }
+    std::copy(digits_.rbegin(), digits_.rend(),
+              std::ostream_iterator<int>(out));
+
+    return out;
+}
+
 void BigNum::flip_sign() {
     assert(is_canonicalized());
 

src/bignum/bignum.hh

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <iosfwd>
 #include <vector>
 
 #include <cstdint>
@@ -10,6 +11,10 @@ class BigNum {
 public:
     explicit BigNum(std::int64_t number);
 
+    friend std::ostream& operator<<(std::ostream& out, BigNum const& num) {
+        return num.dump(out);
+    }
+
     friend BigNum operator+(BigNum const& rhs) {
         return rhs;
     }
@@ -45,6 +50,8 @@ public:
     }
 
 private:
+    std::ostream& dump(std::ostream& out) const;
+
     void flip_sign();
 
     bool equal(BigNum const& rhs) const;

tests/unit/bignum.cc

@@ -1,9 +1,29 @@
+#include <sstream>
+
 #include <gtest/gtest.h>
 
 #include "bignum.hh"
 
 using namespace abacus::bignum;
 
+TEST(BigNum, dump) {
+    auto const zero = BigNum(0);
+    auto const one = BigNum(1);
+    auto const minus_one = BigNum(-1);
+    auto const forty_two = BigNum(42);
+
+    auto const to_str = [](auto num) {
+        std::stringstream str;
+        str << num;
+        return str.str();
+    };
+
+    ASSERT_EQ(to_str(zero), "0");
+    ASSERT_EQ(to_str(one), "1");
+    ASSERT_EQ(to_str(minus_one), "-1");
+    ASSERT_EQ(to_str(forty_two), "42");
+}
+
 TEST(BigNum, equality) {
     auto const zero = BigNum(0);
     auto const one = BigNum(1);