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 #ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
20 __attribute__((__constructor__))
21 #endif
22 static void
23 crc64_init(void)
24 {
25 	static const uint64_t poly64 = UINT64_C(0xC96C5795D7870F42);
26 
27 	for (size_t b = 0; b < 256; ++b) {
28 		uint64_t r = b;
29 		for (size_t i = 0; i < 8; ++i) {
30 			if (r & 1)
31 				r = (r >> 1) ^ poly64;
32 			else
33 				r >>= 1;
34 		}
35 
36 		crc64_table[b] = r;
37 	}
38 
39 	return;
40 }
41 
42 
43 extern LZMA_API(uint64_t)
44 lzma_crc64(const uint8_t *buf, size_t size, uint64_t crc)
45 {
46 #ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
47 	mythread_once(crc64_init);
48 #endif
49 
50 	crc = ~crc;
51 
52 	while (size != 0) {
53 		crc = crc64_table[*buf++ ^ (crc & 0xFF)] ^ (crc >> 8);
54 		--size;
55 	}
56 
57 	return ~crc;
58 }
59