69 lines
2.0 KiB
C++
69 lines
2.0 KiB
C++
//===--- CRC.cpp - Cyclic Redundancy Check implementation -----------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements llvm::crc32 function.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Support/CRC.h"
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#include "llvm/Config/config.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/Support/Threading.h"
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#include <array>
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using namespace llvm;
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#if LLVM_ENABLE_ZLIB == 0 || !HAVE_ZLIB_H
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using CRC32Table = std::array<uint32_t, 256>;
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static void initCRC32Table(CRC32Table *Tbl) {
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auto Shuffle = [](uint32_t V) {
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return (V & 1) ? (V >> 1) ^ 0xEDB88320U : V >> 1;
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};
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for (size_t I = 0; I < Tbl->size(); ++I) {
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uint32_t V = Shuffle(I);
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V = Shuffle(V);
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V = Shuffle(V);
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V = Shuffle(V);
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V = Shuffle(V);
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V = Shuffle(V);
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V = Shuffle(V);
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(*Tbl)[I] = Shuffle(V);
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}
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}
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uint32_t llvm::crc32(uint32_t CRC, StringRef S) {
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static llvm::once_flag InitFlag;
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static CRC32Table Tbl;
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llvm::call_once(InitFlag, initCRC32Table, &Tbl);
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const uint8_t *P = reinterpret_cast<const uint8_t *>(S.data());
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size_t Len = S.size();
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CRC ^= 0xFFFFFFFFU;
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for (; Len >= 8; Len -= 8) {
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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}
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while (Len--)
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CRC = Tbl[(CRC ^ *P++) & 0xFF] ^ (CRC >> 8);
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return CRC ^ 0xFFFFFFFFU;
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}
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#else
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#include <zlib.h>
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uint32_t llvm::crc32(uint32_t CRC, StringRef S) {
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return ::crc32(CRC, (const Bytef *)S.data(), S.size());
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}
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#endif
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