Import fast crc32 from Stephan Brumme

crc32/Crc32.h

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+// //////////////////////////////////////////////////////////
+// Crc32.h
+// Copyright (c) 2011-2019 Stephan Brumme. All rights reserved.
+// Slicing-by-16 contributed by Bulat Ziganshin
+// Tableless bytewise CRC contributed by Hagai Gold
+// see http://create.stephan-brumme.com/disclaimer.html
+//
+
+// if running on an embedded system, you might consider shrinking the
+// big Crc32Lookup table by undefining these lines:
+#define CRC32_USE_LOOKUP_TABLE_BYTE
+#define CRC32_USE_LOOKUP_TABLE_SLICING_BY_4
+#define CRC32_USE_LOOKUP_TABLE_SLICING_BY_8
+#define CRC32_USE_LOOKUP_TABLE_SLICING_BY_16
+// - crc32_bitwise  doesn't need it at all
+// - crc32_halfbyte has its own small lookup table
+// - crc32_1byte_tableless and crc32_1byte_tableless2 don't need it at all
+// - crc32_1byte    needs only Crc32Lookup[0]
+// - crc32_4bytes   needs only Crc32Lookup[0..3]
+// - crc32_8bytes   needs only Crc32Lookup[0..7]
+// - crc32_4x8bytes needs only Crc32Lookup[0..7]
+// - crc32_16bytes  needs all of Crc32Lookup
+// using the aforementioned #defines the table is automatically fitted to your needs
+
+// uint8_t, uint32_t, int32_t
+#include <stdint.h>
+// size_t
+#include <cstddef>
+
+// crc32_fast selects the fastest algorithm depending on flags (CRC32_USE_LOOKUP_...)
+/// compute CRC32 using the fastest algorithm for large datasets on modern CPUs
+uint32_t crc32_fast    (const void* data, size_t length, uint32_t previousCrc32 = 0);
+
+/// merge two CRC32 such that result = crc32(dataB, lengthB, crc32(dataA, lengthA))
+uint32_t crc32_combine (uint32_t crcA, uint32_t crcB, size_t lengthB);
+
+/// compute CRC32 (bitwise algorithm)
+uint32_t crc32_bitwise (const void* data, size_t length, uint32_t previousCrc32 = 0);
+/// compute CRC32 (half-byte algoritm)
+uint32_t crc32_halfbyte(const void* data, size_t length, uint32_t previousCrc32 = 0);
+
+#ifdef CRC32_USE_LOOKUP_TABLE_BYTE
+/// compute CRC32 (standard algorithm)
+uint32_t crc32_1byte   (const void* data, size_t length, uint32_t previousCrc32 = 0);
+#endif
+
+/// compute CRC32 (byte algorithm) without lookup tables
+uint32_t crc32_1byte_tableless (const void* data, size_t length, uint32_t previousCrc32 = 0);
+/// compute CRC32 (byte algorithm) without lookup tables
+uint32_t crc32_1byte_tableless2(const void* data, size_t length, uint32_t previousCrc32 = 0);
+
+#ifdef CRC32_USE_LOOKUP_TABLE_SLICING_BY_4
+/// compute CRC32 (Slicing-by-4 algorithm)
+uint32_t crc32_4bytes  (const void* data, size_t length, uint32_t previousCrc32 = 0);
+#endif
+
+#ifdef CRC32_USE_LOOKUP_TABLE_SLICING_BY_8
+/// compute CRC32 (Slicing-by-8 algorithm)
+uint32_t crc32_8bytes  (const void* data, size_t length, uint32_t previousCrc32 = 0);
+/// compute CRC32 (Slicing-by-8 algorithm), unroll inner loop 4 times
+uint32_t crc32_4x8bytes(const void* data, size_t length, uint32_t previousCrc32 = 0);
+#endif
+
+#ifdef CRC32_USE_LOOKUP_TABLE_SLICING_BY_16
+/// compute CRC32 (Slicing-by-16 algorithm)
+uint32_t crc32_16bytes (const void* data, size_t length, uint32_t previousCrc32 = 0);
+/// compute CRC32 (Slicing-by-16 algorithm, prefetch upcoming data blocks)
+uint32_t crc32_16bytes_prefetch(const void* data, size_t length, uint32_t previousCrc32 = 0, size_t prefetchAhead = 256);
+#endif

crc32/LICENSE

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+zlib License
+
+Copyright (c) 2011-2016 Stephan Brumme
+
+This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
+Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
+1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software.
+   If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
+2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
+3. This notice may not be removed or altered from any source distribution.