1 files changed, 95 insertions, 0 deletions
diff --git a/crypto/src/pqc/crypto/crystals/dilithium/Rounding.cs b/crypto/src/pqc/crypto/crystals/dilithium/Rounding.cs
new file mode 100644
index 000000000..625b60cf5
--- /dev/null
+++ b/crypto/src/pqc/crypto/crystals/dilithium/Rounding.cs
@@ -0,0 +1,95 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Org.BouncyCastle.Pqc.Crypto.Crystals.Dilithium
+{
+    internal class Rounding
+    {
+        public static int[] Power2Round(int a)
+        {
+            int[] r = new int[2];
+
+            r[0] = (a + (1 << (DilithiumEngine.D - 1)) - 1) >> DilithiumEngine.D;
+            r[1] = a - (r[0] << DilithiumEngine.D);
+            return r;
+        }
+
+        public static int[] Decompose(int a, int gamma2)
+        {
+            int a0, a1;
+            a1 = (a + 127) >> 7;
+            if (gamma2 == (DilithiumEngine.Q - 1) / 32)
+            {
+                a1 = (a1 * 1025 + (1 << 21)) >> 22;
+                a1 &= 15;
+            }
+            else if (gamma2 == (DilithiumEngine.Q - 1) / 88)
+            {
+                a1 = (a1 * 11275 + (1 << 23)) >> 24;
+                a1 ^= ((43 - a1) >> 31) & a1;
+            }
+            else
+            {
+                throw new ArgumentException("Wrong Gamma2!");
+            }
+
+            a0 = a - a1 * 2 * gamma2;
+            a0 -= (((DilithiumEngine.Q - 1) / 2 - a0) >> 31) & DilithiumEngine.Q;
+            return new int[] { a0, a1 };
+        }
+
+        public static int MakeHint(int a0, int a1, DilithiumEngine engine)
+        {
+            int g2 = engine.Gamma2, q = DilithiumEngine.Q;
+            if (a0 <= g2 || a0 > q - g2 || (a0 == q - g2 && a1 == 0))
+            {
+                return 0;
+            }
+            return 1;
+        }
+
+        public static int UseHint(int a, int hint, int gamma2)
+        {
+            int a0, a1;
+
+            int[] intArray = Decompose(a, gamma2);
+            a0 = intArray[0];
+            a1 = intArray[1];
+
+            if (hint == 0)
+            {
+                return a1;
+            }
+
+            if (gamma2 == (DilithiumEngine.Q - 1) / 32)
+            {
+                if (a0 > 0)
+                {
+                    return (a1 + 1) & 15;
+                }
+                else
+                {
+                    return (a1 - 1) & 15;
+                }
+            }
+            else if (gamma2 == (DilithiumEngine.Q - 1) / 88)
+            {
+                if (a0 > 0)
+                {
+                    return (a1 == 43) ? 0 : a1 + 1;
+                }
+                else
+                {
+                    return (a1 == 0) ? 43 : a1 - 1;
+                }
+            }
+            else
+            {
+                throw new ArgumentException("Wrong Gamma2!");
+            }
+        }
+    }
+}