1 files changed, 77 insertions, 0 deletions
diff --git a/src/base/bit_stream.h b/src/base/bit_stream.h
new file mode 100644
index 0000000..c878197
--- /dev/null
+++ b/src/base/bit_stream.h
@@ -0,0 +1,77 @@
+// Copyright 2018 Google LLC
+//
+// 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
+//
+//     https://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.
+
+#ifndef ASTC_CODEC_BASE_BIT_STREAM_H_
+#define ASTC_CODEC_BASE_BIT_STREAM_H_
+
+#include <cassert>
+#include <cstdint>
+
+namespace astc_codec {
+namespace base {
+
+// Represents a stream of bits that can be read or written in arbitrary-sized
+// chunks.
+template<typename IntType = uint64_t>
+class BitStream {
+ public:
+  // Creates an empty BitStream.
+  BitStream() = default;
+  BitStream(IntType data, uint32_t data_size)
+      : data_(data), data_size_(data_size) {
+    assert(data_size_ <= sizeof(data_) * 8);
+  }
+
+  // Return the number of bits in the stream.
+  uint32_t Bits() const { return data_size_; }
+
+  // Put |size| bits into the stream.
+  // Fails if there is not enough space in the buffer to store the bits.
+  template<typename ResultType>
+  void PutBits(ResultType x, uint32_t size) {
+    assert(data_size_ + size <= sizeof(data_) * 8);
+
+    data_ |= (IntType(x) & MaskFor(size)) << data_size_;
+    data_size_ += size;
+  }
+
+  // Get |count| bits from the stream.
+  // Returns true if |count| bits were successfully retrieved.
+  template<typename ResultType>
+  bool GetBits(uint32_t count, ResultType* result) {
+    if (count <= data_size_) {
+      *result = static_cast<ResultType>(data_ & MaskFor(count));
+      data_ = data_ >> count;
+      data_size_ -= count;
+      return true;
+    } else {
+      *result = 0;
+      return false;
+    }
+  }
+
+ private:
+  IntType MaskFor(uint32_t bits) const {
+    return (bits == sizeof(IntType) * 8) ? ~IntType(0)
+                                         : (IntType(1) << bits) - 1;
+  }
+
+  IntType data_ = 0;
+  uint32_t data_size_ = 0;
+};
+
+}  // namespace base
+}  // namespace astc_codec
+
+#endif  // ASTC_CODEC_BASE_BIT_STREAM_H_