intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 106 insertions, 0 deletions

diff --git a/contrib/libs/crcutil/rolling_crc.h b/contrib/libs/crcutil/rolling_crc.h
new file mode 100644
index 0000000000..ad4a947e49
--- /dev/null
+++ b/contrib/libs/crcutil/rolling_crc.h
@@ -0,0 +1,106 @@
+// Copyright 2010 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.
+
+// Implements rolling CRC (e.g. for Rabin fingerprinting).
+
+#ifndef CRCUTIL_ROLLING_CRC_H_
+#define CRCUTIL_ROLLING_CRC_H_
+
+#include "base_types.h"   // size_t, uint8
+#include "crc_casts.h"    // TO_BYTE
+
+namespace crcutil {
+
+#pragma pack(push, 16)
+
+// CrcImplementation should provide:
+// - typename Crc
+// - typename TableEntry
+// - typename Word
+// - Crc CrcDefault(const void *data, size_t bytes, const Crc &start)
+// - const GfUtil<Crc> &Base() const
+template<typename CrcImplementation> class RollingCrc {
+ public:
+  typedef typename CrcImplementation::Crc Crc;
+  typedef typename CrcImplementation::TableEntry TableEntry;
+  typedef typename CrcImplementation::Word Word;
+
+  RollingCrc() {}
+
+  // Initializes internal data structures.
+  // Retains reference to "crc" instance -- it is used by Start().
+  RollingCrc(const CrcImplementation &crc,
+             size_t roll_window_bytes,
+             const Crc &start_value) {
+    Init(crc, roll_window_bytes, start_value);
+  }
+
+  // Computes crc of "roll_window_bytes" using
+  // "start_value" of "crc" (see Init()).
+  Crc Start(const void *data) const {
+    return crc_->CrcDefault(data, roll_window_bytes_, start_value_);
+  }
+
+  // Computes CRC of "roll_window_bytes" starting in next position.
+  Crc Roll(const Crc &old_crc, size_t byte_out, size_t byte_in) const {
+    return (old_crc >> 8) ^ in_[TO_BYTE(old_crc) ^ byte_in] ^ out_[byte_out];
+  }
+
+  // Initializes internal data structures.
+  // Retains reference to "crc" instance -- it is used by Start().
+  void Init(const CrcImplementation &crc,
+            size_t roll_window_bytes,
+            const Crc &start_value) {
+    crc_ = &crc;
+    roll_window_bytes_ = roll_window_bytes;
+    start_value_ = start_value;
+
+    Crc add = crc.Base().Canonize() ^ start_value;
+    add = crc.Base().Multiply(add, crc.Base().Xpow8N(roll_window_bytes));
+    add ^= crc.Base().Canonize();
+    Crc mul = crc.Base().One() ^ crc.Base().Xpow8N(1);
+    add = crc.Base().Multiply(add, mul);
+
+    mul = crc.Base().XpowN(8 * roll_window_bytes + crc.Base().Degree());
+    for (size_t i = 0; i < 256; ++i) {
+      out_[i] = static_cast<TableEntry>(
+                    crc.Base().MultiplyUnnormalized(
+                        static_cast<Crc>(i), 8, mul) ^ add);
+    }
+    for (size_t i = 0; i < 256; ++i) {
+      in_[i] = crc.crc_word_[sizeof(Word) - 1][i];
+    }
+  }
+
+  // Returns start value.
+  Crc StartValue() const { return start_value_; }
+
+  // Returns length of roll window.
+  size_t WindowBytes() const { return roll_window_bytes_; }
+
+ protected:
+  TableEntry in_[256];
+  TableEntry out_[256];
+
+  // Used only by Start().
+  Crc start_value_;
+  const CrcImplementation *crc_;
+  size_t roll_window_bytes_;
+} GCC_ALIGN_ATTRIBUTE(16);
+
+#pragma pack(pop)
+
+}  // namespace crcutil
+
+#endif  // CRCUTIL_ROLLING_CRC_H_