xref: /linux/lib/crc32.c (revision bf80eef2212a1e8451df13b52533f4bc31bb4f8e)
1 /*
2  * Aug 8, 2011 Bob Pearson with help from Joakim Tjernlund and George Spelvin
3  * cleaned up code to current version of sparse and added the slicing-by-8
4  * algorithm to the closely similar existing slicing-by-4 algorithm.
5  *
6  * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
7  * Nicer crc32 functions/docs submitted by linux@horizon.com.  Thanks!
8  * Code was from the public domain, copyright abandoned.  Code was
9  * subsequently included in the kernel, thus was re-licensed under the
10  * GNU GPL v2.
11  *
12  * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
13  * Same crc32 function was used in 5 other places in the kernel.
14  * I made one version, and deleted the others.
15  * There are various incantations of crc32().  Some use a seed of 0 or ~0.
16  * Some xor at the end with ~0.  The generic crc32() function takes
17  * seed as an argument, and doesn't xor at the end.  Then individual
18  * users can do whatever they need.
19  *   drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
20  *   fs/jffs2 uses seed 0, doesn't xor with ~0.
21  *   fs/partitions/efi.c uses seed ~0, xor's with ~0.
22  *
23  * This source code is licensed under the GNU General Public License,
24  * Version 2.  See the file COPYING for more details.
25  */
26 
27 /* see: Documentation/staging/crc32.rst for a description of algorithms */
28 
29 #include <linux/crc32.h>
30 #include <linux/crc32poly.h>
31 #include <linux/module.h>
32 #include <linux/types.h>
33 #include <linux/sched.h>
34 #include "crc32defs.h"
35 
36 #if CRC_LE_BITS > 8
37 # define tole(x) ((__force u32) cpu_to_le32(x))
38 #else
39 # define tole(x) (x)
40 #endif
41 
42 #if CRC_BE_BITS > 8
43 # define tobe(x) ((__force u32) cpu_to_be32(x))
44 #else
45 # define tobe(x) (x)
46 #endif
47 
48 #include "crc32table.h"
49 
50 MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
51 MODULE_DESCRIPTION("Various CRC32 calculations");
52 MODULE_LICENSE("GPL");
53 
54 #if CRC_LE_BITS > 8 || CRC_BE_BITS > 8
55 
56 /* implements slicing-by-4 or slicing-by-8 algorithm */
57 static inline u32 __pure
58 crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
59 {
60 # ifdef __LITTLE_ENDIAN
61 #  define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
62 #  define DO_CRC4 (t3[(q) & 255] ^ t2[(q >> 8) & 255] ^ \
63 		   t1[(q >> 16) & 255] ^ t0[(q >> 24) & 255])
64 #  define DO_CRC8 (t7[(q) & 255] ^ t6[(q >> 8) & 255] ^ \
65 		   t5[(q >> 16) & 255] ^ t4[(q >> 24) & 255])
66 # else
67 #  define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
68 #  define DO_CRC4 (t0[(q) & 255] ^ t1[(q >> 8) & 255] ^ \
69 		   t2[(q >> 16) & 255] ^ t3[(q >> 24) & 255])
70 #  define DO_CRC8 (t4[(q) & 255] ^ t5[(q >> 8) & 255] ^ \
71 		   t6[(q >> 16) & 255] ^ t7[(q >> 24) & 255])
72 # endif
73 	const u32 *b;
74 	size_t    rem_len;
75 # ifdef CONFIG_X86
76 	size_t i;
77 # endif
78 	const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];
79 # if CRC_LE_BITS != 32
80 	const u32 *t4 = tab[4], *t5 = tab[5], *t6 = tab[6], *t7 = tab[7];
81 # endif
82 	u32 q;
83 
84 	/* Align it */
85 	if (unlikely((long)buf & 3 && len)) {
86 		do {
87 			DO_CRC(*buf++);
88 		} while ((--len) && ((long)buf)&3);
89 	}
90 
91 # if CRC_LE_BITS == 32
92 	rem_len = len & 3;
93 	len = len >> 2;
94 # else
95 	rem_len = len & 7;
96 	len = len >> 3;
97 # endif
98 
99 	b = (const u32 *)buf;
100 # ifdef CONFIG_X86
101 	--b;
102 	for (i = 0; i < len; i++) {
103 # else
104 	for (--b; len; --len) {
105 # endif
106 		q = crc ^ *++b; /* use pre increment for speed */
107 # if CRC_LE_BITS == 32
108 		crc = DO_CRC4;
109 # else
110 		crc = DO_CRC8;
111 		q = *++b;
112 		crc ^= DO_CRC4;
113 # endif
114 	}
115 	len = rem_len;
116 	/* And the last few bytes */
117 	if (len) {
118 		u8 *p = (u8 *)(b + 1) - 1;
119 # ifdef CONFIG_X86
120 		for (i = 0; i < len; i++)
121 			DO_CRC(*++p); /* use pre increment for speed */
122 # else
123 		do {
124 			DO_CRC(*++p); /* use pre increment for speed */
125 		} while (--len);
126 # endif
127 	}
128 	return crc;
129 #undef DO_CRC
130 #undef DO_CRC4
131 #undef DO_CRC8
132 }
133 #endif
134 
135 
136 /**
137  * crc32_le_generic() - Calculate bitwise little-endian Ethernet AUTODIN II
138  *			CRC32/CRC32C
139  * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for other
140  *	 uses, or the previous crc32/crc32c value if computing incrementally.
141  * @p: pointer to buffer over which CRC32/CRC32C is run
142  * @len: length of buffer @p
143  * @tab: little-endian Ethernet table
144  * @polynomial: CRC32/CRC32c LE polynomial
145  */
146 static inline u32 __pure crc32_le_generic(u32 crc, unsigned char const *p,
147 					  size_t len, const u32 (*tab)[256],
148 					  u32 polynomial)
149 {
150 #if CRC_LE_BITS == 1
151 	int i;
152 	while (len--) {
153 		crc ^= *p++;
154 		for (i = 0; i < 8; i++)
155 			crc = (crc >> 1) ^ ((crc & 1) ? polynomial : 0);
156 	}
157 # elif CRC_LE_BITS == 2
158 	while (len--) {
159 		crc ^= *p++;
160 		crc = (crc >> 2) ^ tab[0][crc & 3];
161 		crc = (crc >> 2) ^ tab[0][crc & 3];
162 		crc = (crc >> 2) ^ tab[0][crc & 3];
163 		crc = (crc >> 2) ^ tab[0][crc & 3];
164 	}
165 # elif CRC_LE_BITS == 4
166 	while (len--) {
167 		crc ^= *p++;
168 		crc = (crc >> 4) ^ tab[0][crc & 15];
169 		crc = (crc >> 4) ^ tab[0][crc & 15];
170 	}
171 # elif CRC_LE_BITS == 8
172 	/* aka Sarwate algorithm */
173 	while (len--) {
174 		crc ^= *p++;
175 		crc = (crc >> 8) ^ tab[0][crc & 255];
176 	}
177 # else
178 	crc = (__force u32) __cpu_to_le32(crc);
179 	crc = crc32_body(crc, p, len, tab);
180 	crc = __le32_to_cpu((__force __le32)crc);
181 #endif
182 	return crc;
183 }
184 
185 #if CRC_LE_BITS == 1
186 u32 __pure __weak crc32_le(u32 crc, unsigned char const *p, size_t len)
187 {
188 	return crc32_le_generic(crc, p, len, NULL, CRC32_POLY_LE);
189 }
190 u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
191 {
192 	return crc32_le_generic(crc, p, len, NULL, CRC32C_POLY_LE);
193 }
194 #else
195 u32 __pure __weak crc32_le(u32 crc, unsigned char const *p, size_t len)
196 {
197 	return crc32_le_generic(crc, p, len, crc32table_le, CRC32_POLY_LE);
198 }
199 u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
200 {
201 	return crc32_le_generic(crc, p, len, crc32ctable_le, CRC32C_POLY_LE);
202 }
203 #endif
204 EXPORT_SYMBOL(crc32_le);
205 EXPORT_SYMBOL(__crc32c_le);
206 
207 u32 __pure crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
208 u32 __pure __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
209 u32 __pure crc32_be_base(u32, unsigned char const *, size_t) __alias(crc32_be);
210 
211 /*
212  * This multiplies the polynomials x and y modulo the given modulus.
213  * This follows the "little-endian" CRC convention that the lsbit
214  * represents the highest power of x, and the msbit represents x^0.
215  */
216 static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus)
217 {
218 	u32 product = x & 1 ? y : 0;
219 	int i;
220 
221 	for (i = 0; i < 31; i++) {
222 		product = (product >> 1) ^ (product & 1 ? modulus : 0);
223 		x >>= 1;
224 		product ^= x & 1 ? y : 0;
225 	}
226 
227 	return product;
228 }
229 
230 /**
231  * crc32_generic_shift - Append @len 0 bytes to crc, in logarithmic time
232  * @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient)
233  * @len: The number of bytes. @crc is multiplied by x^(8*@len)
234  * @polynomial: The modulus used to reduce the result to 32 bits.
235  *
236  * It's possible to parallelize CRC computations by computing a CRC
237  * over separate ranges of a buffer, then summing them.
238  * This shifts the given CRC by 8*len bits (i.e. produces the same effect
239  * as appending len bytes of zero to the data), in time proportional
240  * to log(len).
241  */
242 static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
243 						   u32 polynomial)
244 {
245 	u32 power = polynomial;	/* CRC of x^32 */
246 	int i;
247 
248 	/* Shift up to 32 bits in the simple linear way */
249 	for (i = 0; i < 8 * (int)(len & 3); i++)
250 		crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
251 
252 	len >>= 2;
253 	if (!len)
254 		return crc;
255 
256 	for (;;) {
257 		/* "power" is x^(2^i), modulo the polynomial */
258 		if (len & 1)
259 			crc = gf2_multiply(crc, power, polynomial);
260 
261 		len >>= 1;
262 		if (!len)
263 			break;
264 
265 		/* Square power, advancing to x^(2^(i+1)) */
266 		power = gf2_multiply(power, power, polynomial);
267 	}
268 
269 	return crc;
270 }
271 
272 u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len)
273 {
274 	return crc32_generic_shift(crc, len, CRC32_POLY_LE);
275 }
276 
277 u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len)
278 {
279 	return crc32_generic_shift(crc, len, CRC32C_POLY_LE);
280 }
281 EXPORT_SYMBOL(crc32_le_shift);
282 EXPORT_SYMBOL(__crc32c_le_shift);
283 
284 /**
285  * crc32_be_generic() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
286  * @crc: seed value for computation.  ~0 for Ethernet, sometimes 0 for
287  *	other uses, or the previous crc32 value if computing incrementally.
288  * @p: pointer to buffer over which CRC32 is run
289  * @len: length of buffer @p
290  * @tab: big-endian Ethernet table
291  * @polynomial: CRC32 BE polynomial
292  */
293 static inline u32 __pure crc32_be_generic(u32 crc, unsigned char const *p,
294 					  size_t len, const u32 (*tab)[256],
295 					  u32 polynomial)
296 {
297 #if CRC_BE_BITS == 1
298 	int i;
299 	while (len--) {
300 		crc ^= *p++ << 24;
301 		for (i = 0; i < 8; i++)
302 			crc =
303 			    (crc << 1) ^ ((crc & 0x80000000) ? polynomial :
304 					  0);
305 	}
306 # elif CRC_BE_BITS == 2
307 	while (len--) {
308 		crc ^= *p++ << 24;
309 		crc = (crc << 2) ^ tab[0][crc >> 30];
310 		crc = (crc << 2) ^ tab[0][crc >> 30];
311 		crc = (crc << 2) ^ tab[0][crc >> 30];
312 		crc = (crc << 2) ^ tab[0][crc >> 30];
313 	}
314 # elif CRC_BE_BITS == 4
315 	while (len--) {
316 		crc ^= *p++ << 24;
317 		crc = (crc << 4) ^ tab[0][crc >> 28];
318 		crc = (crc << 4) ^ tab[0][crc >> 28];
319 	}
320 # elif CRC_BE_BITS == 8
321 	while (len--) {
322 		crc ^= *p++ << 24;
323 		crc = (crc << 8) ^ tab[0][crc >> 24];
324 	}
325 # else
326 	crc = (__force u32) __cpu_to_be32(crc);
327 	crc = crc32_body(crc, p, len, tab);
328 	crc = __be32_to_cpu((__force __be32)crc);
329 # endif
330 	return crc;
331 }
332 
333 #if CRC_BE_BITS == 1
334 u32 __pure __weak crc32_be(u32 crc, unsigned char const *p, size_t len)
335 {
336 	return crc32_be_generic(crc, p, len, NULL, CRC32_POLY_BE);
337 }
338 #else
339 u32 __pure __weak crc32_be(u32 crc, unsigned char const *p, size_t len)
340 {
341 	return crc32_be_generic(crc, p, len, crc32table_be, CRC32_POLY_BE);
342 }
343 #endif
344 EXPORT_SYMBOL(crc32_be);
345