diff options
author | LaMont Jones <lamont@debian.org> | 2010-12-29 09:33:45 -0700 |
---|---|---|
committer | LaMont Jones <lamont@debian.org> | 2010-12-29 09:33:45 -0700 |
commit | 4f9e177060fb5ad6e574598aefdf2d5f50a8b54f (patch) | |
tree | 840ca668a45e389792ccebaa1c414211c59ff620 /partx/crc32.c | |
parent | 0d32820f872a43ef8c3021dc9b9741f2b8228b40 (diff) | |
parent | 6c6f2af9e3949197cf7a70255895a2f4451f2319 (diff) | |
download | util-linux-old-4f9e177060fb5ad6e574598aefdf2d5f50a8b54f.tar.gz |
Merge remote branch 'origin/master'
Conflicts:
login-utils/Makefile.am
mount/lomount.c
text-utils/od.1
Diffstat (limited to 'partx/crc32.c')
-rw-r--r-- | partx/crc32.c | 393 |
1 files changed, 0 insertions, 393 deletions
diff --git a/partx/crc32.c b/partx/crc32.c deleted file mode 100644 index 4120f728..00000000 --- a/partx/crc32.c +++ /dev/null @@ -1,393 +0,0 @@ -/* - * crc32.c - * This code is in the public domain; copyright abandoned. - * Liability for non-performance of this code is limited to the amount - * you paid for it. Since it is distributed for free, your refund will - * be very very small. If it breaks, you get to keep both pieces. - */ - -#include "crc32.h" - -#if __GNUC__ >= 3 /* 2.x has "attribute", but only 3.0 has "pure */ -#define attribute(x) __attribute__(x) -#else -#define attribute(x) -#endif - -/* - * There are multiple 16-bit CRC polynomials in common use, but this is - * *the* standard CRC-32 polynomial, first popularized by Ethernet. - * x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x^1+x^0 - */ -#define CRCPOLY_LE 0xedb88320 -#define CRCPOLY_BE 0x04c11db7 - -/* How many bits at a time to use. Requires a table of 4<<CRC_xx_BITS bytes. */ -/* For less performance-sensitive, use 4 */ -#define CRC_LE_BITS 8 -#define CRC_BE_BITS 8 - -/* - * Little-endian CRC computation. Used with serial bit streams sent - * lsbit-first. Be sure to use cpu_to_le32() to append the computed CRC. - */ -#if CRC_LE_BITS > 8 || CRC_LE_BITS < 1 || CRC_LE_BITS & CRC_LE_BITS-1 -# error CRC_LE_BITS must be a power of 2 between 1 and 8 -#endif - -#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. - */ -#define crc32init_le() -#define crc32cleanup_le() -/** - * 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 - * - */ -uint32_t attribute((pure)) crc32_le(uint32_t 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 */ - -static uint32_t *crc32table_le; -/** - * crc32init_le() - allocate and initialize LE table data - * - * crc is the crc of the byte i; other entries are filled in based on the - * fact that crctable[i^j] = crctable[i] ^ crctable[j]. - * - */ -static int -crc32init_le(void) -{ - unsigned i, j; - uint32_t crc = 1; - - crc32table_le = - malloc((1 << CRC_LE_BITS) * sizeof(uint32_t)); - if (!crc32table_le) - return 1; - crc32table_le[0] = 0; - - for (i = 1 << (CRC_LE_BITS - 1); i; i >>= 1) { - crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0); - for (j = 0; j < 1 << CRC_LE_BITS; j += 2 * i) - crc32table_le[i + j] = crc ^ crc32table_le[j]; - } - return 0; -} - -/** - * crc32cleanup_le(): free LE table data - */ -static void -crc32cleanup_le(void) -{ - free(crc32table_le); - crc32table_le = NULL; -} - -/** - * 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 - * - */ -uint32_t attribute((pure)) crc32_le(uint32_t crc, unsigned char const *p, size_t len) -{ - while (len--) { -# if CRC_LE_BITS == 8 - crc = (crc >> 8) ^ crc32table_le[(crc ^ *p++) & 255]; -# elif CRC_LE_BITS == 4 - crc ^= *p++; - crc = (crc >> 4) ^ crc32table_le[crc & 15]; - crc = (crc >> 4) ^ crc32table_le[crc & 15]; -# elif CRC_LE_BITS == 2 - 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]; -# endif - } - return crc; -} -#endif - -/* - * Big-endian CRC computation. Used with serial bit streams sent - * msbit-first. Be sure to use cpu_to_be32() to append the computed CRC. - */ -#if CRC_BE_BITS > 8 || CRC_BE_BITS < 1 || CRC_BE_BITS & CRC_BE_BITS-1 -# error CRC_BE_BITS must be a power of 2 between 1 and 8 -#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. - */ -#define crc32init_be() -#define crc32cleanup_be() - -/** - * 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 - * - */ -uint32_t attribute((pure)) crc32_be(uint32_t 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 */ -static uint32_t *crc32table_be; - -/** - * crc32init_be() - allocate and initialize BE table data - */ -static int -crc32init_be(void) -{ - unsigned i, j; - uint32_t crc = 0x80000000; - - crc32table_be = - malloc((1 << CRC_BE_BITS) * sizeof(uint32_t)); - if (!crc32table_be) - return 1; - crc32table_be[0] = 0; - - for (i = 1; i < 1 << CRC_BE_BITS; i <<= 1) { - crc = (crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE : 0); - for (j = 0; j < i; j++) - crc32table_be[i + j] = crc ^ crc32table_be[j]; - } - return 0; -} - -/** - * crc32cleanup_be(): free BE table data - */ -static void -crc32cleanup_be(void) -{ - free(crc32table_be); - crc32table_be = NULL; -} - - -/** - * 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 - * - */ -uint32_t attribute((pure)) crc32_be(uint32_t crc, unsigned char const *p, size_t len) -{ - while (len--) { -# if CRC_BE_BITS == 8 - crc = (crc << 8) ^ crc32table_be[(crc >> 24) ^ *p++]; -# elif CRC_BE_BITS == 4 - crc ^= *p++ << 24; - crc = (crc << 4) ^ crc32table_be[crc >> 28]; - crc = (crc << 4) ^ crc32table_be[crc >> 28]; -# elif CRC_BE_BITS == 2 - 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]; -# endif - } - return crc; -} -#endif - -/* - * 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. - */ - - -/** - * init_crc32(): generates CRC32 tables - * - * On successful initialization, use count is increased. - * This guarantees that the library functions will stay resident - * in memory, and prevents someone from 'rmmod crc32' while - * a driver that needs it is still loaded. - * This also greatly simplifies drivers, as there's no need - * to call an initialization/cleanup function from each driver. - * Since crc32.o is a library module, there's no requirement - * that the user can unload it. - */ -int -init_crc32(void) -{ - int rc1, rc2, rc; - rc1 = crc32init_le(); - rc2 = crc32init_be(); - rc = rc1 || rc2; - return rc; -} - -/** - * cleanup_crc32(): frees crc32 data when no longer needed - */ -void -cleanup_crc32(void) -{ - crc32cleanup_le(); - crc32cleanup_be(); -} |