Added version 0.2 from V.

crcutil-1.0/code/crc_casts.h

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+// 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.
+
+// Casting between integers and compound CRC types.
+
+#ifndef CRCUTIL_CRC_CASTS_H_
+#define CRCUTIL_CRC_CASTS_H_
+
+#include "base_types.h"   // uint8, uint64
+#include "platform.h"     // __forceinline
+
+namespace crcutil {
+
+// Downcasts a value of (oftentimes larger) Crc type to (smaller base integer)
+// Result type, enabling specialized downcasts implemented by "large integer"
+// classes (e.g. uint128_sse2).
+template<typename Crc, typename Result>
+__forceinline Result Downcast(const Crc &x) {
+  return static_cast<Result>(x);
+}
+
+// Extracts 8 least significant bits from a value of Crc type.
+#define TO_BYTE(x) Downcast<Crc, uint8>(x)
+
+// Converts a pair of uint64 bit values into single value of CRC type.
+// It is caller's responsibility to ensure that the input is correct.
+template<typename Crc>
+__forceinline Crc CrcFromUint64(uint64 lo, uint64 hi = 0) {
+  if (sizeof(Crc) <= sizeof(lo)) {
+    return static_cast<Crc>(lo);
+  } else {
+    // static_cast to keep compiler happy.
+    Crc result = static_cast<Crc>(hi);
+    result = SHIFT_LEFT_SAFE(result, 8 * sizeof(lo));
+    result ^= lo;
+    return result;
+  }
+}
+
+// Converts Crc value to a pair of uint64 values.
+template<typename Crc>
+__forceinline void Uint64FromCrc(const Crc &crc,
+                                 uint64 *lo, uint64 *hi = NULL) {
+  if (sizeof(*lo) >= sizeof(crc)) {
+    *lo = Downcast<Crc, uint64>(crc);
+    if (hi != NULL) {
+      *hi = 0;
+    }
+  } else {
+    *lo = Downcast<Crc, uint64>(crc);
+    *hi = Downcast<Crc, uint64>(SHIFT_RIGHT_SAFE(crc, 8 * sizeof(lo)));
+  }
+}
+
+}  // namespace crcutil
+
+#endif  // CRCUTIL_CRC_CASTS_H_