--- /dev/null
+/*\r
+* Licensed under the Apache License, Version 2.0 (the "License");\r
+* you may not use this file except in compliance with the License.\r
+* You may obtain a copy of the License at\r
+*\r
+* http://www.apache.org/licenses/LICENSE-2.0\r
+*\r
+* Unless required by applicable law or agreed to in writing, software\r
+* distributed under the License is distributed on an "AS IS" BASIS,\r
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\r
+* See the License for the specific language governing permissions and\r
+* limitations under the License.\r
+*/\r
+\r
+using System;\r
+namespace com.google.zxing.common.reedsolomon\r
+{\r
+\r
+ /// <summary> <p>This class contains utility methods for performing mathematical operations over\r
+ /// the Galois Field GF(256). Operations use the primitive polynomial\r
+ /// x^8 + x^4 + x^3 + x^2 + 1 in calculations.</p>\r
+ /// \r
+ /// <p>Throughout this package, elements of GF(256) are represented as an <code>int</code>\r
+ /// for convenience and speed (but at the cost of memory).\r
+ /// Only the bottom 8 bits are really used.</p>\r
+ /// \r
+ /// </summary>\r
+ /// <author> srowen@google.com (Sean Owen)\r
+ /// </author>\r
+ public sealed class GF256\r
+ { \r
+ public static GF256 QR_CODE_FIELD = new GF256(0x011D); // x^8 + x^4 + x^3 + x^2 + 1\r
+ public static GF256 DATA_MATRIX_FIELD = new GF256(0x012D); // x^8 + x^5 + x^3 + x^2 + 1\r
+\r
+ private int[] expTable;\r
+ private int[] logTable;\r
+ private GF256Poly zero;\r
+ private GF256Poly one;\r
+\r
+ /**\r
+ * Create a representation of GF(256) using the given primitive polynomial.\r
+ *\r
+ * @param primitive irreducible polynomial whose coefficients are represented by\r
+ * the bits of an int, where the least-significant bit represents the constant\r
+ * coefficient\r
+ */\r
+ private GF256(int primitive) {\r
+ expTable = new int[256];\r
+ logTable = new int[256];\r
+ int x = 1;\r
+ for (int i = 0; i < 256; i++) {\r
+ expTable[i] = x;\r
+ x <<= 1; // x = x * 2; we're assuming the generator alpha is 2\r
+ if (x >= 0x100) {\r
+ x ^= primitive;\r
+ }\r
+ }\r
+ for (int i = 0; i < 255; i++) {\r
+ logTable[expTable[i]] = i;\r
+ }\r
+ // logTable[0] == 0 but this should never be used\r
+ zero = new GF256Poly(this, new int[]{0});\r
+ one = new GF256Poly(this, new int[]{1});\r
+ }\r
+\r
+ public GF256Poly getZero() {\r
+ return zero;\r
+ }\r
+\r
+ public GF256Poly getOne()\r
+ {\r
+ return one;\r
+ }\r
+\r
+ /**\r
+ * @return the monomial representing coefficient * x^degree\r
+ */\r
+ public GF256Poly buildMonomial(int degree, int coefficient)\r
+ {\r
+ if (degree < 0) {\r
+ throw new ArgumentException();\r
+ }\r
+ if (coefficient == 0) {\r
+ return zero;\r
+ }\r
+ int[] coefficients = new int[degree + 1];\r
+ coefficients[0] = coefficient;\r
+ return new GF256Poly(this, coefficients);\r
+ }\r
+\r
+ /**\r
+ * Implements both addition and subtraction -- they are the same in GF(256).\r
+ *\r
+ * @return sum/difference of a and b\r
+ */\r
+ public static int addOrSubtract(int a, int b) {\r
+ return a ^ b;\r
+ }\r
+\r
+ /**\r
+ * @return 2 to the power of a in GF(256)\r
+ */\r
+ public int exp(int a)\r
+ {\r
+ return expTable[a];\r
+ }\r
+\r
+ /**\r
+ * @return base 2 log of a in GF(256)\r
+ */\r
+ public int log(int a)\r
+ {\r
+ if (a == 0) {\r
+ throw new ArgumentException();\r
+ }\r
+ return logTable[a];\r
+ }\r
+\r
+ /**\r
+ * @return multiplicative inverse of a\r
+ */\r
+ public int inverse(int a)\r
+ {\r
+ if (a == 0) {\r
+ throw new ArithmeticException();\r
+ }\r
+ return expTable[255 - logTable[a]];\r
+ }\r
+\r
+ /**\r
+ * @param a\r
+ * @param b\r
+ * @return product of a and b in GF(256)\r
+ */\r
+ public int multiply(int a, int b)\r
+ {\r
+ if (a == 0 || b == 0) {\r
+ return 0;\r
+ }\r
+ if (a == 1) {\r
+ return b;\r
+ }\r
+ if (b == 1) {\r
+ return a;\r
+ }\r
+ return expTable[(logTable[a] + logTable[b]) % 255];\r
+ }\r
+ \r
+ \r
+ }\r
+}
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projects / zxing.git / blobdiff