move mpint/mpz conversion into separate file

these functions need linking against libgmp

1 files changed, 61 insertions, 0 deletions

diff --git a/rfc4251_gmp.C b/rfc4251_gmp.C
new file mode 100644
index 0000000..d3a664e
--- /dev/null
+++ b/rfc4251_gmp.C
@@ -0,0 +1,61 @@
+/*
+ * rfc4251_gmp.C -- implements mpint/gmp conversions for rfc4251string
+ *
+ * these functions need linking against libgmp
+ *
+ * Copyright (C) 2013 Timo Weingärtner <timo@tiwe.de>
+ *
+ * This file is part of ssh-agent-filter.
+ *
+ * ssh-agent-filter is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * ssh-agent-filter is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with ssh-agent-filter.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "rfc4251.h"
+
+rfc4251string::rfc4251string (mpz_srcptr x) {
+	if (mpz_sgn(x) == 0)
+		return;
+
+	auto const import_positive = [] (mpz_srcptr x, std::vector<char> & value) {
+		size_t bits{mpz_sizeinbase(x, 2)};
+		size_t bytes{(bits + 7) / 8};
+		size_t extrabyte{(bits % 8) == 0}; // need extra byte if MSB is 1 to keep it non-negative
+		if (bytes + extrabyte > std::numeric_limits<uint32_t>::max())
+			throw std::length_error{"32-bit limit for rfc4251string exceeded"};
+		value.resize(bytes + extrabyte);
+		value[0] = 0;
+		mpz_export(value.data() + extrabyte, nullptr, 1, 1, 1, 0, x);
+	};
+	if (mpz_sgn(x) == 1)
+		import_positive(x, value);
+	else {
+		// handle two's complement: add 1, invert all bits
+		mpz_class tmp{x};
+		tmp += 1;
+		import_positive(tmp.get_mpz_t(), value);
+		for (auto & i : value)
+			i ^= 0xff;
+	}
+}
+
+rfc4251string::operator mpz_class () const {
+	mpz_class ret;
+	mpz_import(ret.get_mpz_t(), value.size(), 1, 1, 1, 0, value.data());
+	if (mpz_sizeinbase(ret.get_mpz_t(), 2) == value.size() * 8) { // negative
+		mpz_com(ret.get_mpz_t(), ret.get_mpz_t());
+		ret += 1;
+		mpz_neg(ret.get_mpz_t(), ret.get_mpz_t());
+	}
+	return ret;
+}