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authorLaMont Jones <lamont@debian.org>2010-12-29 09:33:45 -0700
committerLaMont Jones <lamont@debian.org>2010-12-29 09:33:45 -0700
commit4f9e177060fb5ad6e574598aefdf2d5f50a8b54f (patch)
tree840ca668a45e389792ccebaa1c414211c59ff620 /partx/crc32.c
parent0d32820f872a43ef8c3021dc9b9741f2b8228b40 (diff)
parent6c6f2af9e3949197cf7a70255895a2f4451f2319 (diff)
downloadutil-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.c393
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();
-}