aboutsummaryrefslogtreecommitdiff
path: root/src/liblzma/check/crc32_fast.c
blob: 8849a47609adc8283fe5c002432a3d5e9303a840 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
///////////////////////////////////////////////////////////////////////////////
//
/// \file       crc32.c
/// \brief      CRC32 calculation
///
/// There are two methods in this file.
/// crc32_generic uses the slice-by-eight algorithm.
/// It is explained in this document:
/// http://www.intel.com/technology/comms/perfnet/download/CRC_generators.pdf
/// The code in this file is not the same as in Intel's paper, but
/// the basic principle is identical.
///
/// crc32_clmul uses 32/64-bit x86 SSSE3, SSE4.1, and CLMUL instructions.
/// It was derived from
/// https://www.researchgate.net/publication/263424619_Fast_CRC_computation
/// and the public domain code from https://github.com/rawrunprotected/crc
/// (URLs were checked on 2023-09-29).
///
/// FIXME: Builds for 32-bit x86 use crc32_x86.S by default instead
/// of this file and thus CLMUL version isn't available on 32-bit x86
/// unless configured with --disable-assembler. Even then the lookup table
/// isn't omitted in crc32_table.c since it doesn't know that assembly
/// code has been disabled.
//
//  Authors:    Lasse Collin
//              Ilya Kurdyukov
//              Hans Jansen
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "check.h"
#include "crc_common.h"

#ifdef CRC_GENERIC

///////////////////
// Generic CRC32 //
///////////////////

static uint32_t
crc32_generic(const uint8_t *buf, size_t size, uint32_t crc)
{
	crc = ~crc;

#ifdef WORDS_BIGENDIAN
	crc = bswap32(crc);
#endif

	if (size > 8) {
		// Fix the alignment, if needed. The if statement above
		// ensures that this won't read past the end of buf[].
		while ((uintptr_t)(buf) & 7) {
			crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);
			--size;
		}

		// Calculate the position where to stop.
		const uint8_t *const limit = buf + (size & ~(size_t)(7));

		// Calculate how many bytes must be calculated separately
		// before returning the result.
		size &= (size_t)(7);

		// Calculate the CRC32 using the slice-by-eight algorithm.
		while (buf < limit) {
			crc ^= aligned_read32ne(buf);
			buf += 4;

			crc = lzma_crc32_table[7][A(crc)]
			    ^ lzma_crc32_table[6][B(crc)]
			    ^ lzma_crc32_table[5][C(crc)]
			    ^ lzma_crc32_table[4][D(crc)];

			const uint32_t tmp = aligned_read32ne(buf);
			buf += 4;

			// At least with some compilers, it is critical for
			// performance, that the crc variable is XORed
			// between the two table-lookup pairs.
			crc = lzma_crc32_table[3][A(tmp)]
			    ^ lzma_crc32_table[2][B(tmp)]
			    ^ crc
			    ^ lzma_crc32_table[1][C(tmp)]
			    ^ lzma_crc32_table[0][D(tmp)];
		}
	}

	while (size-- != 0)
		crc = lzma_crc32_table[0][*buf++ ^ A(crc)] ^ S8(crc);

#ifdef WORDS_BIGENDIAN
	crc = bswap32(crc);
#endif

	return ~crc;
}
#endif

#if defined(CRC_GENERIC) && defined(CRC_CLMUL)
typedef uint32_t (*crc32_func_type)(
		const uint8_t *buf, size_t size, uint32_t crc);

// Clang 16.0.0 and older has a bug where it marks the ifunc resolver
// function as unused since it is static and never used outside of
// __attribute__((__ifunc__())).
#if defined(HAVE_FUNC_ATTRIBUTE_IFUNC) && defined(__clang__)
#	pragma GCC diagnostic push
#	pragma GCC diagnostic ignored "-Wunused-function"
#endif

static crc32_func_type
crc32_resolve(void)
{
	return lzma_is_clmul_supported() ? &lzma_crc32_clmul : &crc32_generic;
}

#if defined(HAVE_FUNC_ATTRIBUTE_IFUNC) && defined(__clang__)
#	pragma GCC diagnostic pop
#endif

#ifndef HAVE_FUNC_ATTRIBUTE_IFUNC

#ifdef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
#	define CRC32_SET_FUNC_ATTR __attribute__((__constructor__))
static crc32_func_type crc32_func;
#else
#	define CRC32_SET_FUNC_ATTR
static uint32_t crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc);
static crc32_func_type crc32_func = &crc32_dispatch;
#endif

CRC32_SET_FUNC_ATTR
static void
crc32_set_func(void)
{
	crc32_func = crc32_resolve();
	return;
}

#ifndef HAVE_FUNC_ATTRIBUTE_CONSTRUCTOR
static uint32_t
crc32_dispatch(const uint8_t *buf, size_t size, uint32_t crc)
{
	// When __attribute__((__ifunc__(...))) and
	// __attribute__((__constructor__)) isn't supported, set the
	// function pointer without any locking. If multiple threads run
	// the detection code in parallel, they will all end up setting
	// the pointer to the same value. This avoids the use of
	// mythread_once() on every call to lzma_crc32() but this likely
	// isn't strictly standards compliant. Let's change it if it breaks.
	crc32_set_func();
	return crc32_func(buf, size, crc);
}

#endif
#endif
#endif


#ifdef CRC_USE_IFUNC
extern LZMA_API(uint32_t)
lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
		__attribute__((__ifunc__("crc32_resolve")));
#else
extern LZMA_API(uint32_t)
lzma_crc32(const uint8_t *buf, size_t size, uint32_t crc)
{
#if defined(CRC_GENERIC) && defined(CRC_CLMUL)
	// If CLMUL is available, it is the best for non-tiny inputs,
	// being over twice as fast as the generic slice-by-four version.
	// However, for size <= 16 it's different. In the extreme case
	// of size == 1 the generic version can be five times faster.
	// At size >= 8 the CLMUL starts to become reasonable. It
	// varies depending on the alignment of buf too.
	//
	// The above doesn't include the overhead of mythread_once().
	// At least on x86-64 GNU/Linux, pthread_once() is very fast but
	// it still makes lzma_crc32(buf, 1, crc) 50-100 % slower. When
	// size reaches 12-16 bytes the overhead becomes negligible.
	//
	// So using the generic version for size <= 16 may give better
	// performance with tiny inputs but if such inputs happen rarely
	// it's not so obvious because then the lookup table of the
	// generic version may not be in the processor cache.
#ifdef CRC_USE_GENERIC_FOR_SMALL_INPUTS
	if (size <= 16)
		return crc32_generic(buf, size, crc);
#endif

	return crc32_func(buf, size, crc);

#elif defined(CRC_CLMUL)
	return lzma_crc32_clmul(buf, size, crc);

#else
	return crc32_generic(buf, size, crc);
#endif
}
#endif