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 }
54