Loading...
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
50MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
51MODULE_DESCRIPTION("Various CRC32 calculations");
52MODULE_LICENSE("GPL");
53
54#if CRC_LE_BITS > 8 || CRC_BE_BITS > 8
55
56/* implements slicing-by-4 or slicing-by-8 algorithm */
57static inline u32 __pure
58crc32_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 */
146static 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
186u32 __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}
190u32 __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
195u32 __pure __weak crc32_le(u32 crc, unsigned char const *p, size_t len)
196{
197 return crc32_le_generic(crc, p, len,
198 (const u32 (*)[256])crc32table_le, CRC32_POLY_LE);
199}
200u32 __pure __weak __crc32c_le(u32 crc, unsigned char const *p, size_t len)
201{
202 return crc32_le_generic(crc, p, len,
203 (const u32 (*)[256])crc32ctable_le, CRC32C_POLY_LE);
204}
205#endif
206EXPORT_SYMBOL(crc32_le);
207EXPORT_SYMBOL(__crc32c_le);
208
209u32 __pure crc32_le_base(u32, unsigned char const *, size_t) __alias(crc32_le);
210u32 __pure __crc32c_le_base(u32, unsigned char const *, size_t) __alias(__crc32c_le);
211
212/*
213 * This multiplies the polynomials x and y modulo the given modulus.
214 * This follows the "little-endian" CRC convention that the lsbit
215 * represents the highest power of x, and the msbit represents x^0.
216 */
217static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus)
218{
219 u32 product = x & 1 ? y : 0;
220 int i;
221
222 for (i = 0; i < 31; i++) {
223 product = (product >> 1) ^ (product & 1 ? modulus : 0);
224 x >>= 1;
225 product ^= x & 1 ? y : 0;
226 }
227
228 return product;
229}
230
231/**
232 * crc32_generic_shift - Append @len 0 bytes to crc, in logarithmic time
233 * @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient)
234 * @len: The number of bytes. @crc is multiplied by x^(8*@len)
235 * @polynomial: The modulus used to reduce the result to 32 bits.
236 *
237 * It's possible to parallelize CRC computations by computing a CRC
238 * over separate ranges of a buffer, then summing them.
239 * This shifts the given CRC by 8*len bits (i.e. produces the same effect
240 * as appending len bytes of zero to the data), in time proportional
241 * to log(len).
242 */
243static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
244 u32 polynomial)
245{
246 u32 power = polynomial; /* CRC of x^32 */
247 int i;
248
249 /* Shift up to 32 bits in the simple linear way */
250 for (i = 0; i < 8 * (int)(len & 3); i++)
251 crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
252
253 len >>= 2;
254 if (!len)
255 return crc;
256
257 for (;;) {
258 /* "power" is x^(2^i), modulo the polynomial */
259 if (len & 1)
260 crc = gf2_multiply(crc, power, polynomial);
261
262 len >>= 1;
263 if (!len)
264 break;
265
266 /* Square power, advancing to x^(2^(i+1)) */
267 power = gf2_multiply(power, power, polynomial);
268 }
269
270 return crc;
271}
272
273u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len)
274{
275 return crc32_generic_shift(crc, len, CRC32_POLY_LE);
276}
277
278u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len)
279{
280 return crc32_generic_shift(crc, len, CRC32C_POLY_LE);
281}
282EXPORT_SYMBOL(crc32_le_shift);
283EXPORT_SYMBOL(__crc32c_le_shift);
284
285/**
286 * crc32_be_generic() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
287 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
288 * other uses, or the previous crc32 value if computing incrementally.
289 * @p: pointer to buffer over which CRC32 is run
290 * @len: length of buffer @p
291 * @tab: big-endian Ethernet table
292 * @polynomial: CRC32 BE polynomial
293 */
294static inline u32 __pure crc32_be_generic(u32 crc, unsigned char const *p,
295 size_t len, const u32 (*tab)[256],
296 u32 polynomial)
297{
298#if CRC_BE_BITS == 1
299 int i;
300 while (len--) {
301 crc ^= *p++ << 24;
302 for (i = 0; i < 8; i++)
303 crc =
304 (crc << 1) ^ ((crc & 0x80000000) ? polynomial :
305 0);
306 }
307# elif CRC_BE_BITS == 2
308 while (len--) {
309 crc ^= *p++ << 24;
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 crc = (crc << 2) ^ tab[0][crc >> 30];
314 }
315# elif CRC_BE_BITS == 4
316 while (len--) {
317 crc ^= *p++ << 24;
318 crc = (crc << 4) ^ tab[0][crc >> 28];
319 crc = (crc << 4) ^ tab[0][crc >> 28];
320 }
321# elif CRC_BE_BITS == 8
322 while (len--) {
323 crc ^= *p++ << 24;
324 crc = (crc << 8) ^ tab[0][crc >> 24];
325 }
326# else
327 crc = (__force u32) __cpu_to_be32(crc);
328 crc = crc32_body(crc, p, len, tab);
329 crc = __be32_to_cpu((__force __be32)crc);
330# endif
331 return crc;
332}
333
334#if CRC_BE_BITS == 1
335u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
336{
337 return crc32_be_generic(crc, p, len, NULL, CRC32_POLY_BE);
338}
339#else
340u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
341{
342 return crc32_be_generic(crc, p, len,
343 (const u32 (*)[256])crc32table_be, CRC32_POLY_BE);
344}
345#endif
346EXPORT_SYMBOL(crc32_be);
1/*
2 * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
3 * Nicer crc32 functions/docs submitted by linux@horizon.com. Thanks!
4 * Code was from the public domain, copyright abandoned. Code was
5 * subsequently included in the kernel, thus was re-licensed under the
6 * GNU GPL v2.
7 *
8 * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
9 * Same crc32 function was used in 5 other places in the kernel.
10 * I made one version, and deleted the others.
11 * There are various incantations of crc32(). Some use a seed of 0 or ~0.
12 * Some xor at the end with ~0. The generic crc32() function takes
13 * seed as an argument, and doesn't xor at the end. Then individual
14 * users can do whatever they need.
15 * drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
16 * fs/jffs2 uses seed 0, doesn't xor with ~0.
17 * fs/partitions/efi.c uses seed ~0, xor's with ~0.
18 *
19 * This source code is licensed under the GNU General Public License,
20 * Version 2. See the file COPYING for more details.
21 */
22
23#include <linux/crc32.h>
24#include <linux/kernel.h>
25#include <linux/module.h>
26#include <linux/compiler.h>
27#include <linux/types.h>
28#include <linux/init.h>
29#include <linux/atomic.h>
30#include "crc32defs.h"
31#if CRC_LE_BITS == 8
32# define tole(x) __constant_cpu_to_le32(x)
33#else
34# define tole(x) (x)
35#endif
36
37#if CRC_BE_BITS == 8
38# define tobe(x) __constant_cpu_to_be32(x)
39#else
40# define tobe(x) (x)
41#endif
42#include "crc32table.h"
43
44MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
45MODULE_DESCRIPTION("Ethernet CRC32 calculations");
46MODULE_LICENSE("GPL");
47
48#if CRC_LE_BITS == 8 || CRC_BE_BITS == 8
49
50static inline u32
51crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
52{
53# ifdef __LITTLE_ENDIAN
54# define DO_CRC(x) crc = tab[0][(crc ^ (x)) & 255] ^ (crc >> 8)
55# define DO_CRC4 crc = tab[3][(crc) & 255] ^ \
56 tab[2][(crc >> 8) & 255] ^ \
57 tab[1][(crc >> 16) & 255] ^ \
58 tab[0][(crc >> 24) & 255]
59# else
60# define DO_CRC(x) crc = tab[0][((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
61# define DO_CRC4 crc = tab[0][(crc) & 255] ^ \
62 tab[1][(crc >> 8) & 255] ^ \
63 tab[2][(crc >> 16) & 255] ^ \
64 tab[3][(crc >> 24) & 255]
65# endif
66 const u32 *b;
67 size_t rem_len;
68
69 /* Align it */
70 if (unlikely((long)buf & 3 && len)) {
71 do {
72 DO_CRC(*buf++);
73 } while ((--len) && ((long)buf)&3);
74 }
75 rem_len = len & 3;
76 /* load data 32 bits wide, xor data 32 bits wide. */
77 len = len >> 2;
78 b = (const u32 *)buf;
79 for (--b; len; --len) {
80 crc ^= *++b; /* use pre increment for speed */
81 DO_CRC4;
82 }
83 len = rem_len;
84 /* And the last few bytes */
85 if (len) {
86 u8 *p = (u8 *)(b + 1) - 1;
87 do {
88 DO_CRC(*++p); /* use pre increment for speed */
89 } while (--len);
90 }
91 return crc;
92#undef DO_CRC
93#undef DO_CRC4
94}
95#endif
96/**
97 * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
98 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
99 * other uses, or the previous crc32 value if computing incrementally.
100 * @p: pointer to buffer over which CRC is run
101 * @len: length of buffer @p
102 */
103u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
104
105#if CRC_LE_BITS == 1
106/*
107 * In fact, the table-based code will work in this case, but it can be
108 * simplified by inlining the table in ?: form.
109 */
110
111u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
112{
113 int i;
114 while (len--) {
115 crc ^= *p++;
116 for (i = 0; i < 8; i++)
117 crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
118 }
119 return crc;
120}
121#else /* Table-based approach */
122
123u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
124{
125# if CRC_LE_BITS == 8
126 const u32 (*tab)[] = crc32table_le;
127
128 crc = __cpu_to_le32(crc);
129 crc = crc32_body(crc, p, len, tab);
130 return __le32_to_cpu(crc);
131# elif CRC_LE_BITS == 4
132 while (len--) {
133 crc ^= *p++;
134 crc = (crc >> 4) ^ crc32table_le[crc & 15];
135 crc = (crc >> 4) ^ crc32table_le[crc & 15];
136 }
137 return crc;
138# elif CRC_LE_BITS == 2
139 while (len--) {
140 crc ^= *p++;
141 crc = (crc >> 2) ^ crc32table_le[crc & 3];
142 crc = (crc >> 2) ^ crc32table_le[crc & 3];
143 crc = (crc >> 2) ^ crc32table_le[crc & 3];
144 crc = (crc >> 2) ^ crc32table_le[crc & 3];
145 }
146 return crc;
147# endif
148}
149#endif
150
151/**
152 * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
153 * @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
154 * other uses, or the previous crc32 value if computing incrementally.
155 * @p: pointer to buffer over which CRC is run
156 * @len: length of buffer @p
157 */
158u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
159
160#if CRC_BE_BITS == 1
161/*
162 * In fact, the table-based code will work in this case, but it can be
163 * simplified by inlining the table in ?: form.
164 */
165
166u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
167{
168 int i;
169 while (len--) {
170 crc ^= *p++ << 24;
171 for (i = 0; i < 8; i++)
172 crc =
173 (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
174 0);
175 }
176 return crc;
177}
178
179#else /* Table-based approach */
180u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
181{
182# if CRC_BE_BITS == 8
183 const u32 (*tab)[] = crc32table_be;
184
185 crc = __cpu_to_be32(crc);
186 crc = crc32_body(crc, p, len, tab);
187 return __be32_to_cpu(crc);
188# elif CRC_BE_BITS == 4
189 while (len--) {
190 crc ^= *p++ << 24;
191 crc = (crc << 4) ^ crc32table_be[crc >> 28];
192 crc = (crc << 4) ^ crc32table_be[crc >> 28];
193 }
194 return crc;
195# elif CRC_BE_BITS == 2
196 while (len--) {
197 crc ^= *p++ << 24;
198 crc = (crc << 2) ^ crc32table_be[crc >> 30];
199 crc = (crc << 2) ^ crc32table_be[crc >> 30];
200 crc = (crc << 2) ^ crc32table_be[crc >> 30];
201 crc = (crc << 2) ^ crc32table_be[crc >> 30];
202 }
203 return crc;
204# endif
205}
206#endif
207
208EXPORT_SYMBOL(crc32_le);
209EXPORT_SYMBOL(crc32_be);
210
211/*
212 * A brief CRC tutorial.
213 *
214 * A CRC is a long-division remainder. You add the CRC to the message,
215 * and the whole thing (message+CRC) is a multiple of the given
216 * CRC polynomial. To check the CRC, you can either check that the
217 * CRC matches the recomputed value, *or* you can check that the
218 * remainder computed on the message+CRC is 0. This latter approach
219 * is used by a lot of hardware implementations, and is why so many
220 * protocols put the end-of-frame flag after the CRC.
221 *
222 * It's actually the same long division you learned in school, except that
223 * - We're working in binary, so the digits are only 0 and 1, and
224 * - When dividing polynomials, there are no carries. Rather than add and
225 * subtract, we just xor. Thus, we tend to get a bit sloppy about
226 * the difference between adding and subtracting.
227 *
228 * A 32-bit CRC polynomial is actually 33 bits long. But since it's
229 * 33 bits long, bit 32 is always going to be set, so usually the CRC
230 * is written in hex with the most significant bit omitted. (If you're
231 * familiar with the IEEE 754 floating-point format, it's the same idea.)
232 *
233 * Note that a CRC is computed over a string of *bits*, so you have
234 * to decide on the endianness of the bits within each byte. To get
235 * the best error-detecting properties, this should correspond to the
236 * order they're actually sent. For example, standard RS-232 serial is
237 * little-endian; the most significant bit (sometimes used for parity)
238 * is sent last. And when appending a CRC word to a message, you should
239 * do it in the right order, matching the endianness.
240 *
241 * Just like with ordinary division, the remainder is always smaller than
242 * the divisor (the CRC polynomial) you're dividing by. Each step of the
243 * division, you take one more digit (bit) of the dividend and append it
244 * to the current remainder. Then you figure out the appropriate multiple
245 * of the divisor to subtract to being the remainder back into range.
246 * In binary, it's easy - it has to be either 0 or 1, and to make the
247 * XOR cancel, it's just a copy of bit 32 of the remainder.
248 *
249 * When computing a CRC, we don't care about the quotient, so we can
250 * throw the quotient bit away, but subtract the appropriate multiple of
251 * the polynomial from the remainder and we're back to where we started,
252 * ready to process the next bit.
253 *
254 * A big-endian CRC written this way would be coded like:
255 * for (i = 0; i < input_bits; i++) {
256 * multiple = remainder & 0x80000000 ? CRCPOLY : 0;
257 * remainder = (remainder << 1 | next_input_bit()) ^ multiple;
258 * }
259 * Notice how, to get at bit 32 of the shifted remainder, we look
260 * at bit 31 of the remainder *before* shifting it.
261 *
262 * But also notice how the next_input_bit() bits we're shifting into
263 * the remainder don't actually affect any decision-making until
264 * 32 bits later. Thus, the first 32 cycles of this are pretty boring.
265 * Also, to add the CRC to a message, we need a 32-bit-long hole for it at
266 * the end, so we have to add 32 extra cycles shifting in zeros at the
267 * end of every message,
268 *
269 * So the standard trick is to rearrage merging in the next_input_bit()
270 * until the moment it's needed. Then the first 32 cycles can be precomputed,
271 * and merging in the final 32 zero bits to make room for the CRC can be
272 * skipped entirely.
273 * This changes the code to:
274 * for (i = 0; i < input_bits; i++) {
275 * remainder ^= next_input_bit() << 31;
276 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
277 * remainder = (remainder << 1) ^ multiple;
278 * }
279 * With this optimization, the little-endian code is simpler:
280 * for (i = 0; i < input_bits; i++) {
281 * remainder ^= next_input_bit();
282 * multiple = (remainder & 1) ? CRCPOLY : 0;
283 * remainder = (remainder >> 1) ^ multiple;
284 * }
285 *
286 * Note that the other details of endianness have been hidden in CRCPOLY
287 * (which must be bit-reversed) and next_input_bit().
288 *
289 * However, as long as next_input_bit is returning the bits in a sensible
290 * order, we can actually do the merging 8 or more bits at a time rather
291 * than one bit at a time:
292 * for (i = 0; i < input_bytes; i++) {
293 * remainder ^= next_input_byte() << 24;
294 * for (j = 0; j < 8; j++) {
295 * multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
296 * remainder = (remainder << 1) ^ multiple;
297 * }
298 * }
299 * Or in little-endian:
300 * for (i = 0; i < input_bytes; i++) {
301 * remainder ^= next_input_byte();
302 * for (j = 0; j < 8; j++) {
303 * multiple = (remainder & 1) ? CRCPOLY : 0;
304 * remainder = (remainder << 1) ^ multiple;
305 * }
306 * }
307 * If the input is a multiple of 32 bits, you can even XOR in a 32-bit
308 * word at a time and increase the inner loop count to 32.
309 *
310 * You can also mix and match the two loop styles, for example doing the
311 * bulk of a message byte-at-a-time and adding bit-at-a-time processing
312 * for any fractional bytes at the end.
313 *
314 * The only remaining optimization is to the byte-at-a-time table method.
315 * Here, rather than just shifting one bit of the remainder to decide
316 * in the correct multiple to subtract, we can shift a byte at a time.
317 * This produces a 40-bit (rather than a 33-bit) intermediate remainder,
318 * but again the multiple of the polynomial to subtract depends only on
319 * the high bits, the high 8 bits in this case.
320 *
321 * The multiple we need in that case is the low 32 bits of a 40-bit
322 * value whose high 8 bits are given, and which is a multiple of the
323 * generator polynomial. This is simply the CRC-32 of the given
324 * one-byte message.
325 *
326 * Two more details: normally, appending zero bits to a message which
327 * is already a multiple of a polynomial produces a larger multiple of that
328 * polynomial. To enable a CRC to detect this condition, it's common to
329 * invert the CRC before appending it. This makes the remainder of the
330 * message+crc come out not as zero, but some fixed non-zero value.
331 *
332 * The same problem applies to zero bits prepended to the message, and
333 * a similar solution is used. Instead of starting with a remainder of
334 * 0, an initial remainder of all ones is used. As long as you start
335 * the same way on decoding, it doesn't make a difference.
336 */
337
338#ifdef UNITTEST
339
340#include <stdlib.h>
341#include <stdio.h>
342
343#if 0 /*Not used at present */
344static void
345buf_dump(char const *prefix, unsigned char const *buf, size_t len)
346{
347 fputs(prefix, stdout);
348 while (len--)
349 printf(" %02x", *buf++);
350 putchar('\n');
351
352}
353#endif
354
355static void bytereverse(unsigned char *buf, size_t len)
356{
357 while (len--) {
358 unsigned char x = bitrev8(*buf);
359 *buf++ = x;
360 }
361}
362
363static void random_garbage(unsigned char *buf, size_t len)
364{
365 while (len--)
366 *buf++ = (unsigned char) random();
367}
368
369#if 0 /* Not used at present */
370static void store_le(u32 x, unsigned char *buf)
371{
372 buf[0] = (unsigned char) x;
373 buf[1] = (unsigned char) (x >> 8);
374 buf[2] = (unsigned char) (x >> 16);
375 buf[3] = (unsigned char) (x >> 24);
376}
377#endif
378
379static void store_be(u32 x, unsigned char *buf)
380{
381 buf[0] = (unsigned char) (x >> 24);
382 buf[1] = (unsigned char) (x >> 16);
383 buf[2] = (unsigned char) (x >> 8);
384 buf[3] = (unsigned char) x;
385}
386
387/*
388 * This checks that CRC(buf + CRC(buf)) = 0, and that
389 * CRC commutes with bit-reversal. This has the side effect
390 * of bytewise bit-reversing the input buffer, and returns
391 * the CRC of the reversed buffer.
392 */
393static u32 test_step(u32 init, unsigned char *buf, size_t len)
394{
395 u32 crc1, crc2;
396 size_t i;
397
398 crc1 = crc32_be(init, buf, len);
399 store_be(crc1, buf + len);
400 crc2 = crc32_be(init, buf, len + 4);
401 if (crc2)
402 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
403 crc2);
404
405 for (i = 0; i <= len + 4; i++) {
406 crc2 = crc32_be(init, buf, i);
407 crc2 = crc32_be(crc2, buf + i, len + 4 - i);
408 if (crc2)
409 printf("\nCRC split fail: 0x%08x\n", crc2);
410 }
411
412 /* Now swap it around for the other test */
413
414 bytereverse(buf, len + 4);
415 init = bitrev32(init);
416 crc2 = bitrev32(crc1);
417 if (crc1 != bitrev32(crc2))
418 printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
419 crc1, crc2, bitrev32(crc2));
420 crc1 = crc32_le(init, buf, len);
421 if (crc1 != crc2)
422 printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
423 crc2);
424 crc2 = crc32_le(init, buf, len + 4);
425 if (crc2)
426 printf("\nCRC cancellation fail: 0x%08x should be 0\n",
427 crc2);
428
429 for (i = 0; i <= len + 4; i++) {
430 crc2 = crc32_le(init, buf, i);
431 crc2 = crc32_le(crc2, buf + i, len + 4 - i);
432 if (crc2)
433 printf("\nCRC split fail: 0x%08x\n", crc2);
434 }
435
436 return crc1;
437}
438
439#define SIZE 64
440#define INIT1 0
441#define INIT2 0
442
443int main(void)
444{
445 unsigned char buf1[SIZE + 4];
446 unsigned char buf2[SIZE + 4];
447 unsigned char buf3[SIZE + 4];
448 int i, j;
449 u32 crc1, crc2, crc3;
450
451 for (i = 0; i <= SIZE; i++) {
452 printf("\rTesting length %d...", i);
453 fflush(stdout);
454 random_garbage(buf1, i);
455 random_garbage(buf2, i);
456 for (j = 0; j < i; j++)
457 buf3[j] = buf1[j] ^ buf2[j];
458
459 crc1 = test_step(INIT1, buf1, i);
460 crc2 = test_step(INIT2, buf2, i);
461 /* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
462 crc3 = test_step(INIT1 ^ INIT2, buf3, i);
463 if (crc3 != (crc1 ^ crc2))
464 printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n",
465 crc3, crc1, crc2);
466 }
467 printf("\nAll test complete. No failures expected.\n");
468 return 0;
469}
470
471#endif /* UNITTEST */