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1 ///////////////////////////////////////////////////////////////////////////////
2 //
3 /// \file       crc64_small.c
4 /// \brief      CRC64 calculation (size-optimized)
5 //
6 //  Author:     Lasse Collin
7 //
8 //  This file has been put into the public domain.
9 //  You can do whatever you want with this file.
10 //
11 ///////////////////////////////////////////////////////////////////////////////
12
13 #include "check.h"
14
15
16 static uint64_t crc64_table[256];
17
18
19 static void
20 crc64_init(void)
21 {
22         static const uint64_t poly64 = UINT64_C(0xC96C5795D7870F42);
23
24         for (size_t b = 0; b < 256; ++b) {
25                 uint64_t r = b;
26                 for (size_t i = 0; i < 8; ++i) {
27                         if (r & 1)
28                                 r = (r >> 1) ^ poly64;
29                         else
30                                 r >>= 1;
31                 }
32
33                 crc64_table[b] = r;
34         }
35
36         return;
37 }
38
39
40 extern LZMA_API(uint64_t)
41 lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
42 {
43         mythread_once(crc64_init);
44
45         crc = ~crc;
46
47         while (size != 0) {
48                 crc = crc64_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
49                 --size;
50         }
51
52         return ~crc;
53 }