--- /dev/null
+/*\r
+ * Copyright 2007 Google Inc.\r
+ *\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
+package com.google.zxing.common;\r
+\r
+/**\r
+ * <p>This provides an easy abstraction to read bits at a time from a sequence of bytes, where the\r
+ * number of bits read is not often a multiple of 8.</p>\r
+ *\r
+ * <p>This class is not thread-safe.</p>\r
+ *\r
+ * @author srowen@google.com (Sean Owen)\r
+ */\r
+public final class BitSource {\r
+\r
+ private final byte[] bytes;\r
+ private int byteOffset;\r
+ private int bitOffset;\r
+\r
+ /**\r
+ * @param bytes bytes from which this will read bits. Bits will be read from the first byte first.\r
+ * Bits are read within a byte from most-significant to least-significant bit.\r
+ */\r
+ public BitSource(byte[] bytes) {\r
+ this.bytes = bytes;\r
+ }\r
+\r
+ /**\r
+ * @param numBits number of bits to read\r
+ * @return int representing the bits read. The bits will appear as the least-significant\r
+ * bits of the int\r
+ * @throws IllegalArgumentException if numBits isn't in [1,32]\r
+ */\r
+ public int readBits(int numBits) {\r
+ if (numBits < 1 || numBits > 32) {\r
+ throw new IllegalArgumentException();\r
+ }\r
+\r
+ int result = 0;\r
+\r
+ // First, read remainder from current byte\r
+ if (bitOffset > 0) {\r
+ int bitsLeft = 8 - bitOffset;\r
+ int toRead = numBits < bitsLeft ? numBits : bitsLeft;\r
+ int bitsToNotRead = bitsLeft - toRead;\r
+ int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;\r
+ result = (bytes[byteOffset] & mask) >> bitsToNotRead;\r
+ numBits -= toRead;\r
+ bitOffset += toRead;\r
+ if (bitOffset == 8) {\r
+ bitOffset = 0;\r
+ byteOffset++;\r
+ }\r
+ }\r
+\r
+ // Next read whole bytes\r
+ if (numBits > 0) {\r
+ while (numBits >= 8) {\r
+ result = (result << 8) | (bytes[byteOffset] & 0xFF);\r
+ byteOffset++;\r
+ numBits -= 8;\r
+ }\r
+\r
+ // Finally read a partial byte\r
+ if (numBits > 0) {\r
+ int bitsToNotRead = 8 - numBits;\r
+ int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;\r
+ result = (result << numBits) | ((bytes[byteOffset] & mask) >> bitsToNotRead);\r
+ bitOffset += numBits;\r
+ }\r
+ }\r
+\r
+ return result;\r
+ }\r
+\r
+ /**\r
+ * @return number of bits that can be read successfully\r
+ */\r
+ public int available() {\r
+ return 8 * (bytes.length - byteOffset) - bitOffset;\r
+ }\r
+\r
+}\r
--- /dev/null
+/*
+ * Copyright 2007 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.zxing.common;
+
+import junit.framework.TestCase;
+
+/**
+ * @author srowen@google.com (Sean Owen)
+ */
+public final class BitSourceTestCase extends TestCase {
+
+ public void testSource() {
+ byte[] bytes = new byte[]{(byte) 1, (byte) 2, (byte) 3, (byte) 4, (byte) 5};
+ BitSource source = new BitSource(bytes);
+ assertEquals(40, source.available());
+ assertEquals(0, source.readBits(1));
+ assertEquals(39, source.available());
+ assertEquals(0, source.readBits(6));
+ assertEquals(33, source.available());
+ assertEquals(1, source.readBits(1));
+ assertEquals(32, source.available());
+ assertEquals(2, source.readBits(8));
+ assertEquals(24, source.available());
+ assertEquals(12, source.readBits(10));
+ assertEquals(14, source.available());
+ assertEquals(16, source.readBits(8));
+ assertEquals(6, source.available());
+ assertEquals(5, source.readBits(6));
+ assertEquals(0, source.available());
+ }
+
+}
\ No newline at end of file