Import Bech32 C++ reference code & tests

This includes a reformatted version of the Bech32 reference code
(see https://github.com/sipa/bech32/tree/master/ref/c%2B%2B), with
extra documentation.

src/test/bech32_tests.cpp

@@ -0,0 +1,67 @@
+// Copyright (c) 2017 Pieter Wuille
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "bech32.h"
+#include "test/test_bitcoin.h"
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(bech32_tests, BasicTestingSetup)
+
+bool CaseInsensitiveEqual(const std::string &s1, const std::string &s2)
+{
+    if (s1.size() != s2.size()) return false;
+    for (size_t i = 0; i < s1.size(); ++i) {
+        char c1 = s1[i];
+        if (c1 >= 'A' && c1 <= 'Z') c1 -= ('A' - 'a');
+        char c2 = s2[i];
+        if (c2 >= 'A' && c2 <= 'Z') c2 -= ('A' - 'a');
+        if (c1 != c2) return false;
+    }
+    return true;
+}
+
+BOOST_AUTO_TEST_CASE(bip173_testvectors_valid)
+{
+    static const std::string CASES[] = {
+        "A12UEL5L",
+        "a12uel5l",
+        "an83characterlonghumanreadablepartthatcontainsthenumber1andtheexcludedcharactersbio1tt5tgs",
+        "abcdef1qpzry9x8gf2tvdw0s3jn54khce6mua7lmqqqxw",
+        "11qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqc8247j",
+        "split1checkupstagehandshakeupstreamerranterredcaperred2y9e3w",
+        "?1ezyfcl",
+    };
+    for (const std::string& str : CASES) {
+        auto ret = bech32::Decode(str);
+        BOOST_CHECK(!ret.first.empty());
+        std::string recode = bech32::Encode(ret.first, ret.second);
+        BOOST_CHECK(!recode.empty());
+        BOOST_CHECK(CaseInsensitiveEqual(str, recode));
+    }
+}
+
+BOOST_AUTO_TEST_CASE(bip173_testvectors_invalid)
+{
+    static const std::string CASES[] = {
+        " 1nwldj5",
+        "\x7f""1axkwrx",
+        "\x80""1eym55h",
+        "an84characterslonghumanreadablepartthatcontainsthenumber1andtheexcludedcharactersbio1569pvx",
+        "pzry9x0s0muk",
+        "1pzry9x0s0muk",
+        "x1b4n0q5v",
+        "li1dgmt3",
+        "de1lg7wt\xff",
+        "A1G7SGD8",
+        "10a06t8",
+        "1qzzfhee",
+    };
+    for (const std::string& str : CASES) {
+        auto ret = bech32::Decode(str);
+        BOOST_CHECK(ret.first.empty());
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()