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guoling
55 lines
1.6 KiB
C++
55 lines
1.6 KiB
C++
/* crc32.c -- compute the CRC-32 of a data stream
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* Copyright (C) 1995-2006, 2010, 2011, 2012, 2016 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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*
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* Thanks to Rodney Brown <rbrown64@csc.com.au> for his contribution of faster
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* CRC methods: exclusive-oring 32 bits of data at a time, and pre-computing
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* tables for updating the shift register in one step with three exclusive-ors
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* instead of four steps with four exclusive-ors. This results in about a
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* factor of two increase in speed on a Power PC G4 (PPC7455) using gcc -O3.
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*/
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/* @(#) $Id$ */
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#include "../../MMKVPredef.h"
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#if MMKV_EMBED_ZLIB
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#include "zutil.h" /* for STDC and FAR definitions */
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#define Z_NULL 0 /* for initializing zalloc, zfree, opaque */
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# define TBLS 1
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#include "crc32.h"
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namespace zlib {
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/* ========================================================================= */
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#define DO1 crc = crc_table[0][((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8)
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#define DO8 DO1; DO1; DO1; DO1; DO1; DO1; DO1; DO1
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/* ========================================================================= */
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unsigned long local crc32_z(unsigned long crc, const unsigned char FAR *buf, z_size_t len)
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{
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if (buf == Z_NULL) return 0UL;
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crc = crc ^ 0xffffffffUL;
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while (len >= 8) {
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DO8;
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len -= 8;
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}
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if (len) do {
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DO1;
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} while (--len);
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return crc ^ 0xffffffffUL;
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}
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/* ========================================================================= */
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unsigned long ZEXPORT crc32(unsigned long crc, const unsigned char FAR *buf, z_size_t len) {
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return crc32_z(crc, buf, len);
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}
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} // namespace zlib
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#endif // MMKV_EMBED_ZLIB
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