1 files changed, 164 insertions, 0 deletions
diff --git a/extern/draco/draco/src/draco/compression/entropy/rans_symbol_decoder.h b/extern/draco/draco/src/draco/compression/entropy/rans_symbol_decoder.h
new file mode 100644
index 00000000000..10cdc6781a0
--- /dev/null
+++ b/extern/draco/draco/src/draco/compression/entropy/rans_symbol_decoder.h
@@ -0,0 +1,164 @@
+// Copyright 2016 The Draco Authors.
+//
+// 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.
+//
+#ifndef DRACO_COMPRESSION_ENTROPY_RANS_SYMBOL_DECODER_H_
+#define DRACO_COMPRESSION_ENTROPY_RANS_SYMBOL_DECODER_H_
+
+#include "draco/compression/config/compression_shared.h"
+#include "draco/compression/entropy/rans_symbol_coding.h"
+#include "draco/core/decoder_buffer.h"
+#include "draco/core/varint_decoding.h"
+#include "draco/draco_features.h"
+
+namespace draco {
+
+// A helper class for decoding symbols using the rANS algorithm (see ans.h).
+// The class can be used to decode the probability table and the data encoded
+// by the RAnsSymbolEncoder. |unique_symbols_bit_length_t| must be the same as
+// the one used for the corresponding RAnsSymbolEncoder.
+template <int unique_symbols_bit_length_t>
+class RAnsSymbolDecoder {
+ public:
+  RAnsSymbolDecoder() : num_symbols_(0) {}
+
+  // Initialize the decoder and decode the probability table.
+  bool Create(DecoderBuffer *buffer);
+
+  uint32_t num_symbols() const { return num_symbols_; }
+
+  // Starts decoding from the buffer. The buffer will be advanced past the
+  // encoded data after this call.
+  bool StartDecoding(DecoderBuffer *buffer);
+  uint32_t DecodeSymbol() { return ans_.rans_read(); }
+  void EndDecoding();
+
+ private:
+  static constexpr int rans_precision_bits_ =
+      ComputeRAnsPrecisionFromUniqueSymbolsBitLength(
+          unique_symbols_bit_length_t);
+  static constexpr int rans_precision_ = 1 << rans_precision_bits_;
+
+  std::vector<uint32_t> probability_table_;
+  uint32_t num_symbols_;
+  RAnsDecoder<rans_precision_bits_> ans_;
+};
+
+template <int unique_symbols_bit_length_t>
+bool RAnsSymbolDecoder<unique_symbols_bit_length_t>::Create(
+    DecoderBuffer *buffer) {
+  // Check that the DecoderBuffer version is set.
+  if (buffer->bitstream_version() == 0) {
+    return false;
+  }
+  // Decode the number of alphabet symbols.
+#ifdef DRACO_BACKWARDS_COMPATIBILITY_SUPPORTED
+  if (buffer->bitstream_version() < DRACO_BITSTREAM_VERSION(2, 0)) {
+    if (!buffer->Decode(&num_symbols_)) {
+      return false;
+    }
+
+  } else
+#endif
+  {
+    if (!DecodeVarint(&num_symbols_, buffer)) {
+      return false;
+    }
+  }
+  probability_table_.resize(num_symbols_);
+  if (num_symbols_ == 0) {
+    return true;
+  }
+  // Decode the table.
+  for (uint32_t i = 0; i < num_symbols_; ++i) {
+    uint8_t prob_data = 0;
+    // Decode the first byte and extract the number of extra bytes we need to
+    // get, or the offset to the next symbol with non-zero probability.
+    if (!buffer->Decode(&prob_data)) {
+      return false;
+    }
+    // Token is stored in the first two bits of the first byte. Values 0-2 are
+    // used to indicate the number of extra bytes, and value 3 is a special
+    // symbol used to denote run-length coding of zero probability entries.
+    // See rans_symbol_encoder.h for more details.
+    const int token = prob_data & 3;
+    if (token == 3) {
+      const uint32_t offset = prob_data >> 2;
+      if (i + offset >= num_symbols_) {
+        return false;
+      }
+      // Set zero probability for all symbols in the specified range.
+      for (uint32_t j = 0; j < offset + 1; ++j) {
+        probability_table_[i + j] = 0;
+      }
+      i += offset;
+    } else {
+      const int extra_bytes = token;
+      uint32_t prob = prob_data >> 2;
+      for (int b = 0; b < extra_bytes; ++b) {
+        uint8_t eb;
+        if (!buffer->Decode(&eb)) {
+          return false;
+        }
+        // Shift 8 bits for each extra byte and subtract 2 for the two first
+        // bits.
+        prob |= static_cast<uint32_t>(eb) << (8 * (b + 1) - 2);
+      }
+      probability_table_[i] = prob;
+    }
+  }
+  if (!ans_.rans_build_look_up_table(&probability_table_[0], num_symbols_)) {
+    return false;
+  }
+  return true;
+}
+
+template <int unique_symbols_bit_length_t>
+bool RAnsSymbolDecoder<unique_symbols_bit_length_t>::StartDecoding(
+    DecoderBuffer *buffer) {
+  uint64_t bytes_encoded;
+  // Decode the number of bytes encoded by the encoder.
+#ifdef DRACO_BACKWARDS_COMPATIBILITY_SUPPORTED
+  if (buffer->bitstream_version() < DRACO_BITSTREAM_VERSION(2, 0)) {
+    if (!buffer->Decode(&bytes_encoded)) {
+      return false;
+    }
+
+  } else
+#endif
+  {
+    if (!DecodeVarint<uint64_t>(&bytes_encoded, buffer)) {
+      return false;
+    }
+  }
+  if (bytes_encoded > static_cast<uint64_t>(buffer->remaining_size())) {
+    return false;
+  }
+  const uint8_t *const data_head =
+      reinterpret_cast<const uint8_t *>(buffer->data_head());
+  // Advance the buffer past the rANS data.
+  buffer->Advance(bytes_encoded);
+  if (ans_.read_init(data_head, static_cast<int>(bytes_encoded)) != 0) {
+    return false;
+  }
+  return true;
+}
+
+template <int unique_symbols_bit_length_t>
+void RAnsSymbolDecoder<unique_symbols_bit_length_t>::EndDecoding() {
+  ans_.read_end();
+}
+
+}  // namespace draco
+
+#endif  // DRACO_COMPRESSION_ENTROPY_RANS_SYMBOL_DECODER_H_