Add brotli decompressor

This commit is for the decoder for brotli compression format.
Brotli is a generic byte-level compression algorithm.

brotli/dec/bit_reader.h

@@ -0,0 +1,67 @@
+// Copyright 2013 Google Inc. All Rights Reserved.
+//
+// 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.
+//
+// Bit reading helpers
+
+#ifndef BROTLI_DEC_BIT_READER_H_
+#define BROTLI_DEC_BIT_READER_H_
+
+#include "./types.h"
+
+#if defined(__cplusplus) || defined(c_plusplus)
+extern "C" {
+#endif
+
+typedef struct {
+  uint64_t       val_;        // pre-fetched bits
+  const uint8_t* buf_;        // input byte buffer
+  size_t         len_;        // buffer length
+  size_t         pos_;        // byte position in buf_
+  int            bit_pos_;    // current bit-reading position in val_
+  int            eos_;        // bitstream is finished
+  int            error_;      // an error occurred (buffer overflow attempt...)
+} BrotliBitReader;
+
+void BrotliInitBitReader(BrotliBitReader* const br,
+                         const uint8_t* const start,
+                         size_t length);
+
+//  Sets a new data buffer.
+void BrotliBitReaderSetBuffer(BrotliBitReader* const br,
+                              const uint8_t* const buffer, size_t length);
+
+// Reads the specified number of bits from Read Buffer.
+// Flags an error in case end_of_stream or n_bits is more than allowed limit.
+// Flags eos if this read attempt is going to cross the read buffer.
+uint32_t BrotliReadBits(BrotliBitReader* const br, int n_bits);
+
+// Return the prefetched bits, so they can be looked up.
+static BROTLI_INLINE uint32_t BrotliPrefetchBits(BrotliBitReader* const br) {
+  return (uint32_t)(br->val_ >> br->bit_pos_);
+}
+
+// For jumping over a number of bits in the bit stream when accessed with
+// BrotliPrefetchBits and BrotliFillBitWindow.
+static BROTLI_INLINE void BrotliSetBitPos(BrotliBitReader* const br, int val) {
+  br->bit_pos_ = val;
+}
+
+// Advances the Read buffer by 4 bytes to make room for reading next 32 bits.
+void BrotliFillBitWindow(BrotliBitReader* const br);
+
+#if defined(__cplusplus) || defined(c_plusplus)
+}    // extern "C"
+#endif
+
+#endif  // BROTLI_DEC_BIT_READER_H_