1 files changed, 125 insertions, 0 deletions
diff --git a/extern/draco/draco/src/draco/compression/bit_coders/rans_bit_encoder.cc b/extern/draco/draco/src/draco/compression/bit_coders/rans_bit_encoder.cc
new file mode 100644
index 00000000000..8d00ea35292
--- /dev/null
+++ b/extern/draco/draco/src/draco/compression/bit_coders/rans_bit_encoder.cc
@@ -0,0 +1,125 @@
+// 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.
+//
+#include "draco/compression/bit_coders/rans_bit_encoder.h"
+
+#include "draco/compression/entropy/ans.h"
+#include "draco/core/bit_utils.h"
+#include "draco/core/varint_encoding.h"
+
+namespace draco {
+
+RAnsBitEncoder::RAnsBitEncoder() : local_bits_(0), num_local_bits_(0) {}
+
+RAnsBitEncoder::~RAnsBitEncoder() { Clear(); }
+
+void RAnsBitEncoder::StartEncoding() { Clear(); }
+
+void RAnsBitEncoder::EncodeBit(bool bit) {
+  if (bit) {
+    bit_counts_[1]++;
+    local_bits_ |= 1 << num_local_bits_;
+  } else {
+    bit_counts_[0]++;
+  }
+  num_local_bits_++;
+
+  if (num_local_bits_ == 32) {
+    bits_.push_back(local_bits_);
+    num_local_bits_ = 0;
+    local_bits_ = 0;
+  }
+}
+
+void RAnsBitEncoder::EncodeLeastSignificantBits32(int nbits, uint32_t value) {
+  DRACO_DCHECK_EQ(true, nbits <= 32);
+  DRACO_DCHECK_EQ(true, nbits > 0);
+
+  const uint32_t reversed = ReverseBits32(value) >> (32 - nbits);
+  const int ones = CountOneBits32(reversed);
+  bit_counts_[0] += (nbits - ones);
+  bit_counts_[1] += ones;
+
+  const int remaining = 32 - num_local_bits_;
+
+  if (nbits <= remaining) {
+    CopyBits32(&local_bits_, num_local_bits_, reversed, 0, nbits);
+    num_local_bits_ += nbits;
+    if (num_local_bits_ == 32) {
+      bits_.push_back(local_bits_);
+      local_bits_ = 0;
+      num_local_bits_ = 0;
+    }
+  } else {
+    CopyBits32(&local_bits_, num_local_bits_, reversed, 0, remaining);
+    bits_.push_back(local_bits_);
+    local_bits_ = 0;
+    CopyBits32(&local_bits_, 0, reversed, remaining, nbits - remaining);
+    num_local_bits_ = nbits - remaining;
+  }
+}
+
+void RAnsBitEncoder::EndEncoding(EncoderBuffer *target_buffer) {
+  uint64_t total = bit_counts_[1] + bit_counts_[0];
+  if (total == 0) {
+    total++;
+  }
+
+  // The probability interval [0,1] is mapped to values of [0, 256]. However,
+  // the coding scheme can not deal with probabilities of 0 or 1, which is why
+  // we must clamp the values to interval [1, 255]. Specifically 128
+  // corresponds to 0.5 exactly. And the value can be given as uint8_t.
+  const uint32_t zero_prob_raw = static_cast<uint32_t>(
+      ((bit_counts_[0] / static_cast<double>(total)) * 256.0) + 0.5);
+
+  uint8_t zero_prob = 255;
+  if (zero_prob_raw < 255) {
+    zero_prob = static_cast<uint8_t>(zero_prob_raw);
+  }
+
+  zero_prob += (zero_prob == 0);
+
+  // Space for 32 bit integer and some extra space.
+  std::vector<uint8_t> buffer((bits_.size() + 8) * 8);
+  AnsCoder ans_coder;
+  ans_write_init(&ans_coder, buffer.data());
+
+  for (int i = num_local_bits_ - 1; i >= 0; --i) {
+    const uint8_t bit = (local_bits_ >> i) & 1;
+    rabs_write(&ans_coder, bit, zero_prob);
+  }
+  for (auto it = bits_.rbegin(); it != bits_.rend(); ++it) {
+    const uint32_t bits = *it;
+    for (int i = 31; i >= 0; --i) {
+      const uint8_t bit = (bits >> i) & 1;
+      rabs_write(&ans_coder, bit, zero_prob);
+    }
+  }
+
+  const int size_in_bytes = ans_write_end(&ans_coder);
+  target_buffer->Encode(zero_prob);
+  EncodeVarint(static_cast<uint32_t>(size_in_bytes), target_buffer);
+  target_buffer->Encode(buffer.data(), size_in_bytes);
+
+  Clear();
+}
+
+void RAnsBitEncoder::Clear() {
+  bit_counts_.assign(2, 0);
+  bits_.clear();
+  local_bits_ = 0;
+  num_local_bits_ = 0;
+}
+
+}  // namespace draco