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Packages/com.voidbotz.fonepayunity/Runtime/QR/FonepayQRGenerator.ReedSolomon.cs

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+using System;
+
+namespace Darkmatter.Fonepay
+{
+    public static partial class FonepayQRGenerator
+    {
+        static readonly byte[] _exp = new byte[512];
+        static readonly byte[] _log = new byte[256];
+
+        static FonepayQRGenerator()
+        {
+            int x = 1;
+            for (int i = 0; i < 255; i++)
+            {
+                _exp[i] = (byte)x;
+                _log[x] = (byte)i;
+                x <<= 1;
+                if (x >= 256) x ^= 0x11d;
+            }
+            for (int i = 255; i < 512; i++) _exp[i] = _exp[i - 255];
+        }
+
+        static byte GfMul(byte a, byte b)
+        {
+            if (a == 0 || b == 0) return 0;
+            return _exp[(_log[a] + _log[b]) % 255];
+        }
+
+        static byte GfPow(int b, int e) => _exp[(_log[(byte)b] * e) % 255];
+
+        static byte[] ReedSolomon(byte[] data, int ecCount)
+        {
+            byte[] gen = RsGenerator(ecCount);
+            byte[] msg = new byte[data.Length + ecCount];
+            Array.Copy(data, msg, data.Length);
+
+            for (int i = 0; i < data.Length; i++)
+            {
+                byte coef = msg[i];
+                if (coef == 0) continue;
+                for (int j = 1; j < gen.Length; j++)
+                    msg[i + j] ^= GfMul(gen[j], coef);
+            }
+
+            byte[] ec = new byte[ecCount];
+            Array.Copy(msg, data.Length, ec, 0, ecCount);
+            return ec;
+        }
+
+        static byte[] RsGenerator(int degree)
+        {
+            byte[] g = { 1 };
+            for (int i = 0; i < degree; i++)
+            {
+                byte[] ng = new byte[g.Length + 1];
+                byte root = GfPow(2, i);
+                for (int j = 0; j < g.Length; j++)
+                {
+                    ng[j] ^= GfMul(g[j], root);
+                    ng[j + 1] ^= g[j];
+                }
+                g = ng;
+            }
+            return g;
+        }
+    }
+}