csharp/common/reedsolomon/ReedSolomonEncoder.cs

   1 /*\r
   2 * Licensed under the Apache License, Version 2.0 (the "License");\r
   3 * you may not use this file except in compliance with the License.\r
   4 * You may obtain a copy of the License at\r
   5 *\r
   6 *      http://www.apache.org/licenses/LICENSE-2.0\r
   7 *\r
   8 * Unless required by applicable law or agreed to in writing, software\r
   9 * distributed under the License is distributed on an "AS IS" BASIS,\r
  10 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\r
  11 * See the License for the specific language governing permissions and\r
  12 * limitations under the License.\r
  13 */\r
  14 \r
  15 using System;\r
  16 using System.Collections;\r
  17 \r
  18 namespace com.google.zxing.common.reedsolomon\r
  19 {\r
  20     public sealed class ReedSolomonEncoder\r
  21     { \r
  22           private GF256 Field;\r
  23           private ArrayList  cachedGenerators;\r
  24 \r
  25           public ReedSolomonEncoder(GF256 field) {\r
  26             if (!GF256.QR_CODE_FIELD.Equals(field)) {\r
  27               throw new ArgumentException("Only QR Code is supported at this time");\r
  28             }\r
  29             this.Field = field;\r
  30             this.cachedGenerators = new ArrayList();\r
  31             cachedGenerators.Add(new GF256Poly(field, new int[] { 1 }));\r
  32           }\r
  33 \r
  34           private GF256Poly buildGenerator(int degree) {\r
  35             if (degree >= cachedGenerators.Count) {\r
  36                 GF256Poly lastGenerator = (GF256Poly)cachedGenerators[(cachedGenerators.Count - 1)];\r
  37               for (int d = cachedGenerators.Count; d <= degree; d++)\r
  38               {\r
  39                   GF256Poly nextGenerator = lastGenerator.multiply(new GF256Poly(Field, new int[] { 1, Field.exp(d - 1) }));\r
  40                 cachedGenerators.Add(nextGenerator);\r
  41                 lastGenerator = nextGenerator;\r
  42               }\r
  43             }\r
  44             return (GF256Poly) cachedGenerators[(degree)];    \r
  45           }\r
  46 \r
  47           public void encode(int[] toEncode, int ecBytes) {\r
  48             if (ecBytes == 0) {\r
  49               throw new ArgumentException("No error correction bytes");\r
  50             }\r
  51             int dataBytes = toEncode.Length - ecBytes;\r
  52             if (dataBytes <= 0) {\r
  53               throw new ArgumentException("No data bytes provided");\r
  54             }\r
  55             GF256Poly generator = buildGenerator(ecBytes);\r
  56             int[] infoCoefficients = new int[dataBytes];\r
  57             System.Array.Copy(toEncode, 0, infoCoefficients, 0, dataBytes);\r
  58             GF256Poly info = new GF256Poly(this.Field, infoCoefficients);\r
  59             info = info.multiplyByMonomial(ecBytes, 1);\r
  60             GF256Poly remainder = info.divide(generator)[1];\r
  61             int[] coefficients = remainder.getCoefficients();\r
  62             int numZeroCoefficients = ecBytes - coefficients.Length;\r
  63             for (int i = 0; i < numZeroCoefficients; i++) {\r
  64               toEncode[dataBytes + i] = 0;\r
  65             }\r
  66             System.Array.Copy(coefficients, 0, toEncode, dataBytes + numZeroCoefficients, coefficients.Length);\r
  67           }\r
  68     \r
  69     }\r
  70 }