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Diffstat (limited to 'lib/crc32.c')
| -rw-r--r-- | lib/crc32.c | 529 |
1 files changed, 529 insertions, 0 deletions
diff --git a/lib/crc32.c b/lib/crc32.c new file mode 100644 index 00000000000..58b222783f9 --- /dev/null +++ b/lib/crc32.c @@ -0,0 +1,529 @@ +/* + * Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com> + * Nicer crc32 functions/docs submitted by linux@horizon.com. Thanks! + * Code was from the public domain, copyright abandoned. Code was + * subsequently included in the kernel, thus was re-licensed under the + * GNU GPL v2. + * + * Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com> + * Same crc32 function was used in 5 other places in the kernel. + * I made one version, and deleted the others. + * There are various incantations of crc32(). Some use a seed of 0 or ~0. + * Some xor at the end with ~0. The generic crc32() function takes + * seed as an argument, and doesn't xor at the end. Then individual + * users can do whatever they need. + * drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0. + * fs/jffs2 uses seed 0, doesn't xor with ~0. + * fs/partitions/efi.c uses seed ~0, xor's with ~0. + * + * This source code is licensed under the GNU General Public License, + * Version 2. See the file COPYING for more details. + */ + +#include <linux/crc32.h> +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/compiler.h> +#include <linux/types.h> +#include <linux/slab.h> +#include <linux/init.h> +#include <asm/atomic.h> +#include "crc32defs.h" +#if CRC_LE_BITS == 8 +#define tole(x) __constant_cpu_to_le32(x) +#define tobe(x) __constant_cpu_to_be32(x) +#else +#define tole(x) (x) +#define tobe(x) (x) +#endif +#include "crc32table.h" + +MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>"); +MODULE_DESCRIPTION("Ethernet CRC32 calculations"); +MODULE_LICENSE("GPL"); + +#if CRC_LE_BITS == 1 +/* + * In fact, the table-based code will work in this case, but it can be + * simplified by inlining the table in ?: form. + */ + +/** + * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32 + * @crc - seed value for computation. ~0 for Ethernet, sometimes 0 for + * other uses, or the previous crc32 value if computing incrementally. + * @p - pointer to buffer over which CRC is run + * @len - length of buffer @p + * + */ +u32 __attribute_pure__ crc32_le(u32 crc, unsigned char const *p, size_t len) +{ + int i; + while (len--) { + crc ^= *p++; + for (i = 0; i < 8; i++) + crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0); + } + return crc; +} +#else /* Table-based approach */ + +/** + * crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32 + * @crc - seed value for computation. ~0 for Ethernet, sometimes 0 for + * other uses, or the previous crc32 value if computing incrementally. + * @p - pointer to buffer over which CRC is run + * @len - length of buffer @p + * + */ +u32 __attribute_pure__ crc32_le(u32 crc, unsigned char const *p, size_t len) +{ +# if CRC_LE_BITS == 8 + const u32 *b =(u32 *)p; + const u32 *tab = crc32table_le; + +# ifdef __LITTLE_ENDIAN +# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8) +# else +# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8) +# endif + + crc = __cpu_to_le32(crc); + /* Align it */ + if(unlikely(((long)b)&3 && len)){ + do { + u8 *p = (u8 *)b; + DO_CRC(*p++); + b = (void *)p; + } while ((--len) && ((long)b)&3 ); + } + if(likely(len >= 4)){ + /* load data 32 bits wide, xor data 32 bits wide. */ + size_t save_len = len & 3; + len = len >> 2; + --b; /* use pre increment below(*++b) for speed */ + do { + crc ^= *++b; + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); + } while (--len); + b++; /* point to next byte(s) */ + len = save_len; + } + /* And the last few bytes */ + if(len){ + do { + u8 *p = (u8 *)b; + DO_CRC(*p++); + b = (void *)p; + } while (--len); + } + + return __le32_to_cpu(crc); +#undef ENDIAN_SHIFT +#undef DO_CRC + +# elif CRC_LE_BITS == 4 + while (len--) { + crc ^= *p++; + crc = (crc >> 4) ^ crc32table_le[crc & 15]; + crc = (crc >> 4) ^ crc32table_le[crc & 15]; + } + return crc; +# elif CRC_LE_BITS == 2 + while (len--) { + crc ^= *p++; + crc = (crc >> 2) ^ crc32table_le[crc & 3]; + crc = (crc >> 2) ^ crc32table_le[crc & 3]; + crc = (crc >> 2) ^ crc32table_le[crc & 3]; + crc = (crc >> 2) ^ crc32table_le[crc & 3]; + } + return crc; +# endif +} +#endif + +#if CRC_BE_BITS == 1 +/* + * In fact, the table-based code will work in this case, but it can be + * simplified by inlining the table in ?: form. + */ + +/** + * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32 + * @crc - seed value for computation. ~0 for Ethernet, sometimes 0 for + * other uses, or the previous crc32 value if computing incrementally. + * @p - pointer to buffer over which CRC is run + * @len - length of buffer @p + * + */ +u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len) +{ + int i; + while (len--) { + crc ^= *p++ << 24; + for (i = 0; i < 8; i++) + crc = + (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE : + 0); + } + return crc; +} + +#else /* Table-based approach */ +/** + * crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32 + * @crc - seed value for computation. ~0 for Ethernet, sometimes 0 for + * other uses, or the previous crc32 value if computing incrementally. + * @p - pointer to buffer over which CRC is run + * @len - length of buffer @p + * + */ +u32 __attribute_pure__ crc32_be(u32 crc, unsigned char const *p, size_t len) +{ +# if CRC_BE_BITS == 8 + const u32 *b =(u32 *)p; + const u32 *tab = crc32table_be; + +# ifdef __LITTLE_ENDIAN +# define DO_CRC(x) crc = tab[ (crc ^ (x)) & 255 ] ^ (crc>>8) +# else +# define DO_CRC(x) crc = tab[ ((crc >> 24) ^ (x)) & 255] ^ (crc<<8) +# endif + + crc = __cpu_to_be32(crc); + /* Align it */ + if(unlikely(((long)b)&3 && len)){ + do { + u8 *p = (u8 *)b; + DO_CRC(*p++); + b = (u32 *)p; + } while ((--len) && ((long)b)&3 ); + } + if(likely(len >= 4)){ + /* load data 32 bits wide, xor data 32 bits wide. */ + size_t save_len = len & 3; + len = len >> 2; + --b; /* use pre increment below(*++b) for speed */ + do { + crc ^= *++b; + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); + DO_CRC(0); + } while (--len); + b++; /* point to next byte(s) */ + len = save_len; + } + /* And the last few bytes */ + if(len){ + do { + u8 *p = (u8 *)b; + DO_CRC(*p++); + b = (void *)p; + } while (--len); + } + return __be32_to_cpu(crc); +#undef ENDIAN_SHIFT +#undef DO_CRC + +# elif CRC_BE_BITS == 4 + while (len--) { + crc ^= *p++ << 24; + crc = (crc << 4) ^ crc32table_be[crc >> 28]; + crc = (crc << 4) ^ crc32table_be[crc >> 28]; + } + return crc; +# elif CRC_BE_BITS == 2 + while (len--) { + crc ^= *p++ << 24; + crc = (crc << 2) ^ crc32table_be[crc >> 30]; + crc = (crc << 2) ^ crc32table_be[crc >> 30]; + crc = (crc << 2) ^ crc32table_be[crc >> 30]; + crc = (crc << 2) ^ crc32table_be[crc >> 30]; + } + return crc; +# endif +} +#endif + +u32 bitreverse(u32 x) +{ + x = (x >> 16) | (x << 16); + x = (x >> 8 & 0x00ff00ff) | (x << 8 & 0xff00ff00); + x = (x >> 4 & 0x0f0f0f0f) | (x << 4 & 0xf0f0f0f0); + x = (x >> 2 & 0x33333333) | (x << 2 & 0xcccccccc); + x = (x >> 1 & 0x55555555) | (x << 1 & 0xaaaaaaaa); + return x; +} + +EXPORT_SYMBOL(crc32_le); +EXPORT_SYMBOL(crc32_be); +EXPORT_SYMBOL(bitreverse); + +/* + * A brief CRC tutorial. + * + * A CRC is a long-division remainder. You add the CRC to the message, + * and the whole thing (message+CRC) is a multiple of the given + * CRC polynomial. To check the CRC, you can either check that the + * CRC matches the recomputed value, *or* you can check that the + * remainder computed on the message+CRC is 0. This latter approach + * is used by a lot of hardware implementations, and is why so many + * protocols put the end-of-frame flag after the CRC. + * + * It's actually the same long division you learned in school, except that + * - We're working in binary, so the digits are only 0 and 1, and + * - When dividing polynomials, there are no carries. Rather than add and + * subtract, we just xor. Thus, we tend to get a bit sloppy about + * the difference between adding and subtracting. + * + * A 32-bit CRC polynomial is actually 33 bits long. But since it's + * 33 bits long, bit 32 is always going to be set, so usually the CRC + * is written in hex with the most significant bit omitted. (If you're + * familiar with the IEEE 754 floating-point format, it's the same idea.) + * + * Note that a CRC is computed over a string of *bits*, so you have + * to decide on the endianness of the bits within each byte. To get + * the best error-detecting properties, this should correspond to the + * order they're actually sent. For example, standard RS-232 serial is + * little-endian; the most significant bit (sometimes used for parity) + * is sent last. And when appending a CRC word to a message, you should + * do it in the right order, matching the endianness. + * + * Just like with ordinary division, the remainder is always smaller than + * the divisor (the CRC polynomial) you're dividing by. Each step of the + * division, you take one more digit (bit) of the dividend and append it + * to the current remainder. Then you figure out the appropriate multiple + * of the divisor to subtract to being the remainder back into range. + * In binary, it's easy - it has to be either 0 or 1, and to make the + * XOR cancel, it's just a copy of bit 32 of the remainder. + * + * When computing a CRC, we don't care about the quotient, so we can + * throw the quotient bit away, but subtract the appropriate multiple of + * the polynomial from the remainder and we're back to where we started, + * ready to process the next bit. + * + * A big-endian CRC written this way would be coded like: + * for (i = 0; i < input_bits; i++) { + * multiple = remainder & 0x80000000 ? CRCPOLY : 0; + * remainder = (remainder << 1 | next_input_bit()) ^ multiple; + * } + * Notice how, to get at bit 32 of the shifted remainder, we look + * at bit 31 of the remainder *before* shifting it. + * + * But also notice how the next_input_bit() bits we're shifting into + * the remainder don't actually affect any decision-making until + * 32 bits later. Thus, the first 32 cycles of this are pretty boring. + * Also, to add the CRC to a message, we need a 32-bit-long hole for it at + * the end, so we have to add 32 extra cycles shifting in zeros at the + * end of every message, + * + * So the standard trick is to rearrage merging in the next_input_bit() + * until the moment it's needed. Then the first 32 cycles can be precomputed, + * and merging in the final 32 zero bits to make room for the CRC can be + * skipped entirely. + * This changes the code to: + * for (i = 0; i < input_bits; i++) { + * remainder ^= next_input_bit() << 31; + * multiple = (remainder & 0x80000000) ? CRCPOLY : 0; + * remainder = (remainder << 1) ^ multiple; + * } + * With this optimization, the little-endian code is simpler: + * for (i = 0; i < input_bits; i++) { + * remainder ^= next_input_bit(); + * multiple = (remainder & 1) ? CRCPOLY : 0; + * remainder = (remainder >> 1) ^ multiple; + * } + * + * Note that the other details of endianness have been hidden in CRCPOLY + * (which must be bit-reversed) and next_input_bit(). + * + * However, as long as next_input_bit is returning the bits in a sensible + * order, we can actually do the merging 8 or more bits at a time rather + * than one bit at a time: + * for (i = 0; i < input_bytes; i++) { + * remainder ^= next_input_byte() << 24; + * for (j = 0; j < 8; j++) { + * multiple = (remainder & 0x80000000) ? CRCPOLY : 0; + * remainder = (remainder << 1) ^ multiple; + * } + * } + * Or in little-endian: + * for (i = 0; i < input_bytes; i++) { + * remainder ^= next_input_byte(); + * for (j = 0; j < 8; j++) { + * multiple = (remainder & 1) ? CRCPOLY : 0; + * remainder = (remainder << 1) ^ multiple; + * } + * } + * If the input is a multiple of 32 bits, you can even XOR in a 32-bit + * word at a time and increase the inner loop count to 32. + * + * You can also mix and match the two loop styles, for example doing the + * bulk of a message byte-at-a-time and adding bit-at-a-time processing + * for any fractional bytes at the end. + * + * The only remaining optimization is to the byte-at-a-time table method. + * Here, rather than just shifting one bit of the remainder to decide + * in the correct multiple to subtract, we can shift a byte at a time. + * This produces a 40-bit (rather than a 33-bit) intermediate remainder, + * but again the multiple of the polynomial to subtract depends only on + * the high bits, the high 8 bits in this case. + * + * The multile we need in that case is the low 32 bits of a 40-bit + * value whose high 8 bits are given, and which is a multiple of the + * generator polynomial. This is simply the CRC-32 of the given + * one-byte message. + * + * Two more details: normally, appending zero bits to a message which + * is already a multiple of a polynomial produces a larger multiple of that + * polynomial. To enable a CRC to detect this condition, it's common to + * invert the CRC before appending it. This makes the remainder of the + * message+crc come out not as zero, but some fixed non-zero value. + * + * The same problem applies to zero bits prepended to the message, and + * a similar solution is used. Instead of starting with a remainder of + * 0, an initial remainder of all ones is used. As long as you start + * the same way on decoding, it doesn't make a difference. + */ + +#ifdef UNITTEST + +#include <stdlib.h> +#include <stdio.h> + +#if 0 /*Not used at present */ +static void +buf_dump(char const *prefix, unsigned char const *buf, size_t len) +{ + fputs(prefix, stdout); + while (len--) + printf(" %02x", *buf++); + putchar('\n'); + +} +#endif + +static void bytereverse(unsigned char *buf, size_t len) +{ + while (len--) { + unsigned char x = *buf; + x = (x >> 4) | (x << 4); + x = (x >> 2 & 0x33) | (x << 2 & 0xcc); + x = (x >> 1 & 0x55) | (x << 1 & 0xaa); + *buf++ = x; + } +} + +static void random_garbage(unsigned char *buf, size_t len) +{ + while (len--) + *buf++ = (unsigned char) random(); +} + +#if 0 /* Not used at present */ +static void store_le(u32 x, unsigned char *buf) +{ + buf[0] = (unsigned char) x; + buf[1] = (unsigned char) (x >> 8); + buf[2] = (unsigned char) (x >> 16); + buf[3] = (unsigned char) (x >> 24); +} +#endif + +static void store_be(u32 x, unsigned char *buf) +{ + buf[0] = (unsigned char) (x >> 24); + buf[1] = (unsigned char) (x >> 16); + buf[2] = (unsigned char) (x >> 8); + buf[3] = (unsigned char) x; +} + +/* + * This checks that CRC(buf + CRC(buf)) = 0, and that + * CRC commutes with bit-reversal. This has the side effect + * of bytewise bit-reversing the input buffer, and returns + * the CRC of the reversed buffer. + */ +static u32 test_step(u32 init, unsigned char *buf, size_t len) +{ + u32 crc1, crc2; + size_t i; + + crc1 = crc32_be(init, buf, len); + store_be(crc1, buf + len); + crc2 = crc32_be(init, buf, len + 4); + if (crc2) + printf("\nCRC cancellation fail: 0x%08x should be 0\n", + crc2); + + for (i = 0; i <= len + 4; i++) { + crc2 = crc32_be(init, buf, i); + crc2 = crc32_be(crc2, buf + i, len + 4 - i); + if (crc2) + printf("\nCRC split fail: 0x%08x\n", crc2); + } + + /* Now swap it around for the other test */ + + bytereverse(buf, len + 4); + init = bitreverse(init); + crc2 = bitreverse(crc1); + if (crc1 != bitreverse(crc2)) + printf("\nBit reversal fail: 0x%08x -> %0x08x -> 0x%08x\n", + crc1, crc2, bitreverse(crc2)); + crc1 = crc32_le(init, buf, len); + if (crc1 != crc2) + printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1, + crc2); + crc2 = crc32_le(init, buf, len + 4); + if (crc2) + printf("\nCRC cancellation fail: 0x%08x should be 0\n", + crc2); + + for (i = 0; i <= len + 4; i++) { + crc2 = crc32_le(init, buf, i); + crc2 = crc32_le(crc2, buf + i, len + 4 - i); + if (crc2) + printf("\nCRC split fail: 0x%08x\n", crc2); + } + + return crc1; +} + +#define SIZE 64 +#define INIT1 0 +#define INIT2 0 + +int main(void) +{ + unsigned char buf1[SIZE + 4]; + unsigned char buf2[SIZE + 4]; + unsigned char buf3[SIZE + 4]; + int i, j; + u32 crc1, crc2, crc3; + + for (i = 0; i <= SIZE; i++) { + printf("\rTesting length %d...", i); + fflush(stdout); + random_garbage(buf1, i); + random_garbage(buf2, i); + for (j = 0; j < i; j++) + buf3[j] = buf1[j] ^ buf2[j]; + + crc1 = test_step(INIT1, buf1, i); + crc2 = test_step(INIT2, buf2, i); + /* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */ + crc3 = test_step(INIT1 ^ INIT2, buf3, i); + if (crc3 != (crc1 ^ crc2)) + printf("CRC XOR fail: 0x%08x != 0x%08x ^ 0x%08x\n", + crc3, crc1, crc2); + } + printf("\nAll test complete. No failures expected.\n"); + return 0; +} + +#endif /* UNITTEST */ |