From 9907b61c574baf0747747f1c512f7cdd88ebed25 Mon Sep 17 00:00:00 2001 From: KunoiSayami Date: Tue, 9 Nov 2021 22:00:01 +0800 Subject: init --- util/crc32c.h | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 util/crc32c.h (limited to 'util/crc32c.h') diff --git a/util/crc32c.h b/util/crc32c.h new file mode 100644 index 0000000..b420b5f --- /dev/null +++ b/util/crc32c.h @@ -0,0 +1,43 @@ +// Copyright (c) 2011 The LevelDB Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. See the AUTHORS file for names of contributors. + +#ifndef STORAGE_LEVELDB_UTIL_CRC32C_H_ +#define STORAGE_LEVELDB_UTIL_CRC32C_H_ + +#include +#include + +namespace leveldb { +namespace crc32c { + +// Return the crc32c of concat(A, data[0,n-1]) where init_crc is the +// crc32c of some string A. Extend() is often used to maintain the +// crc32c of a stream of data. +uint32_t Extend(uint32_t init_crc, const char* data, size_t n); + +// Return the crc32c of data[0,n-1] +inline uint32_t Value(const char* data, size_t n) { return Extend(0, data, n); } + +static const uint32_t kMaskDelta = 0xa282ead8ul; + +// Return a masked representation of crc. +// +// Motivation: it is problematic to compute the CRC of a string that +// contains embedded CRCs. Therefore we recommend that CRCs stored +// somewhere (e.g., in files) should be masked before being stored. +inline uint32_t Mask(uint32_t crc) { + // Rotate right by 15 bits and add a constant. + return ((crc >> 15) | (crc << 17)) + kMaskDelta; +} + +// Return the crc whose masked representation is masked_crc. +inline uint32_t Unmask(uint32_t masked_crc) { + uint32_t rot = masked_crc - kMaskDelta; + return ((rot >> 17) | (rot << 15)); +} + +} // namespace crc32c +} // namespace leveldb + +#endif // STORAGE_LEVELDB_UTIL_CRC32C_H_ -- cgit v1.3.1