1 files changed, 117 insertions, 0 deletions
diff --git a/src/utils/bit_reader.cc b/src/utils/bit_reader.cc
new file mode 100644
index 0000000..3234128
--- /dev/null
+++ b/src/utils/bit_reader.cc
@@ -0,0 +1,117 @@
+// Copyright 2019 The libgav1 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 "src/utils/bit_reader.h"
+
+#include <cassert>
+#include <cstdint>
+
+#include "src/utils/common.h"
+
+namespace libgav1 {
+namespace {
+
+bool Assign(int* const value, int assignment, bool return_value) {
+  *value = assignment;
+  return return_value;
+}
+
+// 5.9.29.
+int InverseRecenter(int r, int v) {
+  if (v > (r << 1)) {
+    return v;
+  }
+  if ((v & 1) != 0) {
+    return r - ((v + 1) >> 1);
+  }
+  return r + (v >> 1);
+}
+
+}  // namespace
+
+bool BitReader::DecodeSignedSubexpWithReference(int low, int high,
+                                                int reference, int control,
+                                                int* const value) {
+  if (!DecodeUnsignedSubexpWithReference(high - low, reference - low, control,
+                                         value)) {
+    return false;
+  }
+  *value += low;
+  return true;
+}
+
+bool BitReader::DecodeUniform(int n, int* const value) {
+  if (n <= 1) {
+    return Assign(value, 0, true);
+  }
+  const int w = FloorLog2(n) + 1;
+  const int m = (1 << w) - n;
+  assert(w - 1 < 32);
+  const int v = static_cast<int>(ReadLiteral(w - 1));
+  if (v == -1) {
+    return Assign(value, 0, false);
+  }
+  if (v < m) {
+    return Assign(value, v, true);
+  }
+  const int extra_bit = ReadBit();
+  if (extra_bit == -1) {
+    return Assign(value, 0, false);
+  }
+  return Assign(value, (v << 1) - m + extra_bit, true);
+}
+
+bool BitReader::DecodeUnsignedSubexpWithReference(int mx, int reference,
+                                                  int control,
+                                                  int* const value) {
+  int v;
+  if (!DecodeSubexp(mx, control, &v)) return false;
+  if ((reference << 1) <= mx) {
+    *value = InverseRecenter(reference, v);
+  } else {
+    *value = mx - 1 - InverseRecenter(mx - 1 - reference, v);
+  }
+  return true;
+}
+
+bool BitReader::DecodeSubexp(int num_symbols, int control, int* const value) {
+  int i = 0;
+  int mk = 0;
+  while (true) {
+    const int b = (i != 0) ? control + i - 1 : control;
+    if (b >= 32) {
+      return Assign(value, 0, false);
+    }
+    const int a = 1 << b;
+    if (num_symbols <= mk + 3 * a) {
+      if (!DecodeUniform(num_symbols - mk, value)) return false;
+      *value += mk;
+      return true;
+    }
+    const int8_t subexp_more_bits = ReadBit();
+    if (subexp_more_bits == -1) return false;
+    if (subexp_more_bits != 0) {
+      ++i;
+      mk += a;
+    } else {
+      const int subexp_bits = static_cast<int>(ReadLiteral(b));
+      if (subexp_bits == -1) {
+        return Assign(value, 0, false);
+      }
+      return Assign(value, subexp_bits + mk, true);
+    }
+  }
+}
+
+}  // namespace libgav1