go.cypherpunks.ru namespace usage

[gogost.git] / mgm / mul.go

diff --git a/mgm/mul.go b/mgm/mul.go
new file mode 100644 (file)
index 0000000..7e0daae
--- /dev/null
+++ b/mgm/mul.go
@@ -0,0 +1,43 @@
+// GoGOST -- Pure Go GOST cryptographic functions library
+// Copyright (C) 2015-2019 Sergey Matveev <stargrave@stargrave.org>
+//
+// This program 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, version 3 of the License.
+//
+// This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package mgm
+
+func (mgm *MGM) mul(xBuf, yBuf []byte) []byte {
+       mgm.x.SetBytes(xBuf)
+       mgm.y.SetBytes(yBuf)
+       mgm.z.SetInt64(0)
+       var i int
+       for mgm.y.BitLen() != 0 {
+               if mgm.y.Bit(0) == 1 {
+                       mgm.z.Xor(mgm.z, mgm.x)
+               }
+               if mgm.x.Bit(mgm.maxBit) == 1 {
+                       mgm.x.SetBit(mgm.x, mgm.maxBit, 0)
+                       mgm.x.Lsh(mgm.x, 1)
+                       mgm.x.Xor(mgm.x, mgm.r)
+               } else {
+                       mgm.x.Lsh(mgm.x, 1)
+               }
+               mgm.y.Rsh(mgm.y, 1)
+       }
+       zBytes := mgm.z.Bytes()
+       rem := len(xBuf) - len(zBytes)
+       for i = 0; i < rem; i++ {
+               mgm.mulBuf[i] = 0
+       }
+       copy(mgm.mulBuf[rem:], zBytes)
+       return mgm.mulBuf
+}