Add Java port of Brotli decoder.

java/dec/BitReader.java

@@ -0,0 +1,171 @@
+/* Copyright 2015 Google Inc. All Rights Reserved.
+
+   Distributed under MIT license.
+   See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
+*/
+
+package org.brotli.dec;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.IntBuffer;
+
+/**
+ * Bit reading helpers.
+ */
+class BitReader {
+
+  /**
+   * Input byte buffer, consist of a ring-buffer and a "slack" region where bytes from the start of
+   * the ring-buffer are copied.
+   */
+  private static final int READ_SIZE = 4096;
+  private static final int BUF_SIZE = READ_SIZE + 64;
+
+  private final ByteBuffer byteBuffer =
+      ByteBuffer.allocateDirect(BUF_SIZE).order(ByteOrder.LITTLE_ENDIAN);
+  private final IntBuffer intBuffer = byteBuffer.asIntBuffer();
+  private final byte[] shadowBuffer = new byte[BUF_SIZE];
+
+  private InputStream input;
+
+  /**
+   * Input stream is finished.
+   */
+  private boolean endOfStreamReached;
+
+  /**
+   * Pre-fetched bits.
+   */
+  long accumulator;
+
+  /**
+   * Current bit-reading position in accumulator.
+   */
+  int bitOffset;
+
+  /**
+   * Number of 32-bit integers availabale for reading.
+   */
+  private int available;
+
+  /* Number of bytes in unfinished "int" item. */
+  private int tailBytes = 0;
+
+  /**
+   * Fills up the input buffer.
+   *
+   * <p> No-op if there are at least 36 bytes present after current position.
+   *
+   * <p> After encountering the end of the input stream, 64 additional zero bytes are copied to the
+   * buffer.
+   */
+  // TODO: Split to check and read; move read outside of decoding loop.
+  static void readMoreInput(BitReader br) {
+    if (br.available > 9) {
+      return;
+    }
+    if (br.endOfStreamReached) {
+      if (br.available > 4) {
+        return;
+      }
+      throw new BrotliRuntimeException("No more input");
+    }
+    int readOffset = br.intBuffer.position() << 2;
+    int bytesRead = READ_SIZE - readOffset;
+    System.arraycopy(br.shadowBuffer, readOffset, br.shadowBuffer, 0, bytesRead);
+    try {
+      while (bytesRead < READ_SIZE) {
+        int len = br.input.read(br.shadowBuffer, bytesRead, READ_SIZE - bytesRead);
+        if (len == -1) {
+          br.endOfStreamReached = true;
+          Utils.fillWithZeroes(br.shadowBuffer, bytesRead, 64);
+          bytesRead += 64;
+          br.tailBytes = bytesRead & 3;
+          break;
+        }
+        bytesRead += len;
+      }
+    } catch (IOException e) {
+      throw new BrotliRuntimeException("Failed to read input", e);
+    }
+    br.byteBuffer.clear();
+    br.byteBuffer.put(br.shadowBuffer, 0, bytesRead & 0xFFFC);
+    br.intBuffer.rewind();
+    br.available = bytesRead >> 2;
+  }
+
+  static void checkHealth(BitReader br) {
+    if (!br.endOfStreamReached) {
+      return;
+    }
+    /* When end of stream is reached, we "borrow" up to 64 zeroes to bit reader.
+     * If compressed stream is valid, then borrowed zeroes should remain unused. */
+    int valentBytes = (br.available << 2) + ((64 - br.bitOffset) >> 3);
+    int borrowedBytes = 64 - br.tailBytes;
+    if (valentBytes != borrowedBytes) {
+      throw new BrotliRuntimeException("Read after end");
+    }
+  }
+
+  /**
+   * Advances the Read buffer by 5 bytes to make room for reading next 24 bits.
+   */
+  static void fillBitWindow(BitReader br) {
+    if (br.bitOffset >= 32) {
+      br.accumulator = ((long) br.intBuffer.get() << 32) | (br.accumulator >>> 32);
+      br.bitOffset -= 32;
+      br.available--;
+    }
+  }
+
+  /**
+   * Reads the specified number of bits from Read Buffer.
+   */
+  static int readBits(BitReader br, int n) {
+    fillBitWindow(br);
+    int val = (int) (br.accumulator >>> br.bitOffset) & ((1 << n) - 1);
+    br.bitOffset += n;
+    return val;
+  }
+
+  /**
+   * Initialize bit reader.
+   *
+   * <p> Initialisation turns bit reader to a ready state. Also a number of bytes is prefetched to
+   * accumulator. Because of that this method may block until enough data could be read from input.
+   *
+   * @param br BitReader POJO
+   * @param input data source
+   */
+  static void init(BitReader br, InputStream input) {
+    if (br.input != null) {
+      throw new IllegalStateException("Bit reader already has associated input stream");
+    }
+    br.input = input;
+    br.accumulator = 0;
+    br.intBuffer.position(READ_SIZE >> 2);
+    br.bitOffset = 64;
+    br.available = 0;
+    br.endOfStreamReached = false;
+    readMoreInput(br);
+    if (br.available == 0) {
+      throw new BrotliRuntimeException("Can't initialize reader");
+    }
+    fillBitWindow(br);
+    fillBitWindow(br);
+  }
+
+  static void jumpToByteBoundry(BitReader br) {
+    int padding = (64 - br.bitOffset) & 7;
+    if (padding != 0) {
+      int paddingBits = BitReader.readBits(br, padding);
+      if (paddingBits != 0) {
+        throw new BrotliRuntimeException("Corrupted padding bits ");
+      }
+    }
+  }
+
+}