466 lines
14 KiB
C
466 lines
14 KiB
C
/*
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* Oct 15, 2000 Matt Domsch <Matt_Domsch@dell.com>
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* Nicer crc32 functions/docs submitted by linux@horizon.com. Thanks!
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* Code was from the public domain, copyright abandoned. Code was
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* subsequently included in the kernel, thus was re-licensed under the
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* GNU GPL v2.
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*
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* Oct 12, 2000 Matt Domsch <Matt_Domsch@dell.com>
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* Same crc32 function was used in 5 other places in the kernel.
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* I made one version, and deleted the others.
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* There are various incantations of crc32(). Some use a seed of 0 or ~0.
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* Some xor at the end with ~0. The generic crc32() function takes
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* seed as an argument, and doesn't xor at the end. Then individual
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* users can do whatever they need.
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* drivers/net/smc9194.c uses seed ~0, doesn't xor with ~0.
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* fs/jffs2 uses seed 0, doesn't xor with ~0.
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* fs/partitions/efi.c uses seed ~0, xor's with ~0.
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*
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* This source code is licensed under the GNU General Public License,
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* Version 2. See the file COPYING for more details.
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*/
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#include <linux/crc32.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/compiler.h>
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#include <linux/types.h>
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#include <linux/init.h>
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#include <asm/atomic.h>
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#include "crc32defs.h"
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#if CRC_LE_BITS == 8
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# define tole(x) __constant_cpu_to_le32(x)
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#else
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# define tole(x) (x)
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#endif
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#if CRC_BE_BITS == 8
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# define tobe(x) __constant_cpu_to_be32(x)
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#else
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# define tobe(x) (x)
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#endif
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#include "crc32table.h"
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MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
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MODULE_DESCRIPTION("Ethernet CRC32 calculations");
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MODULE_LICENSE("GPL");
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#if CRC_LE_BITS == 8 || CRC_BE_BITS == 8
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static inline u32
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crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 *tab)
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{
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# ifdef __LITTLE_ENDIAN
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# define DO_CRC(x) crc = tab[(crc ^ (x)) & 255 ] ^ (crc >> 8)
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# else
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# define DO_CRC(x) crc = tab[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
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# endif
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const u32 *b;
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size_t rem_len;
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/* Align it */
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if (unlikely((long)buf & 3 && len)) {
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do {
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DO_CRC(*buf++);
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} while ((--len) && ((long)buf)&3);
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}
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rem_len = len & 3;
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/* load data 32 bits wide, xor data 32 bits wide. */
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len = len >> 2;
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b = (const u32 *)buf;
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for (--b; len; --len) {
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crc ^= *++b; /* use pre increment for speed */
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DO_CRC(0);
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DO_CRC(0);
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DO_CRC(0);
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DO_CRC(0);
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}
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len = rem_len;
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/* And the last few bytes */
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if (len) {
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u8 *p = (u8 *)(b + 1) - 1;
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do {
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DO_CRC(*++p); /* use pre increment for speed */
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} while (--len);
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}
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return crc;
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#undef DO_CRC
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}
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#endif
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/**
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* crc32_le() - Calculate bitwise little-endian Ethernet AUTODIN II CRC32
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* @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
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* other uses, or the previous crc32 value if computing incrementally.
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* @p: pointer to buffer over which CRC is run
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* @len: length of buffer @p
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*/
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u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
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#if CRC_LE_BITS == 1
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/*
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* In fact, the table-based code will work in this case, but it can be
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* simplified by inlining the table in ?: form.
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*/
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u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
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{
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int i;
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while (len--) {
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crc ^= *p++;
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for (i = 0; i < 8; i++)
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crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0);
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}
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return crc;
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}
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#else /* Table-based approach */
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u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
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{
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# if CRC_LE_BITS == 8
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const u32 *tab = crc32table_le;
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crc = __cpu_to_le32(crc);
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crc = crc32_body(crc, p, len, tab);
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return __le32_to_cpu(crc);
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# elif CRC_LE_BITS == 4
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while (len--) {
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crc ^= *p++;
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crc = (crc >> 4) ^ crc32table_le[crc & 15];
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crc = (crc >> 4) ^ crc32table_le[crc & 15];
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}
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return crc;
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# elif CRC_LE_BITS == 2
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while (len--) {
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crc ^= *p++;
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crc = (crc >> 2) ^ crc32table_le[crc & 3];
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crc = (crc >> 2) ^ crc32table_le[crc & 3];
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crc = (crc >> 2) ^ crc32table_le[crc & 3];
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crc = (crc >> 2) ^ crc32table_le[crc & 3];
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}
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return crc;
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# endif
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}
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#endif
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/**
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* crc32_be() - Calculate bitwise big-endian Ethernet AUTODIN II CRC32
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* @crc: seed value for computation. ~0 for Ethernet, sometimes 0 for
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* other uses, or the previous crc32 value if computing incrementally.
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* @p: pointer to buffer over which CRC is run
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* @len: length of buffer @p
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*/
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u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
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#if CRC_BE_BITS == 1
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/*
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* In fact, the table-based code will work in this case, but it can be
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* simplified by inlining the table in ?: form.
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*/
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u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
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{
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int i;
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while (len--) {
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crc ^= *p++ << 24;
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for (i = 0; i < 8; i++)
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crc =
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(crc << 1) ^ ((crc & 0x80000000) ? CRCPOLY_BE :
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0);
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}
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return crc;
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}
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#else /* Table-based approach */
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u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
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{
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# if CRC_BE_BITS == 8
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const u32 *tab = crc32table_be;
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crc = __cpu_to_be32(crc);
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crc = crc32_body(crc, p, len, tab);
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return __be32_to_cpu(crc);
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# elif CRC_BE_BITS == 4
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while (len--) {
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crc ^= *p++ << 24;
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crc = (crc << 4) ^ crc32table_be[crc >> 28];
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crc = (crc << 4) ^ crc32table_be[crc >> 28];
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}
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return crc;
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# elif CRC_BE_BITS == 2
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while (len--) {
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crc ^= *p++ << 24;
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crc = (crc << 2) ^ crc32table_be[crc >> 30];
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crc = (crc << 2) ^ crc32table_be[crc >> 30];
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crc = (crc << 2) ^ crc32table_be[crc >> 30];
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crc = (crc << 2) ^ crc32table_be[crc >> 30];
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}
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return crc;
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# endif
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}
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#endif
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EXPORT_SYMBOL(crc32_le);
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EXPORT_SYMBOL(crc32_be);
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/*
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* A brief CRC tutorial.
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*
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* A CRC is a long-division remainder. You add the CRC to the message,
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* and the whole thing (message+CRC) is a multiple of the given
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* CRC polynomial. To check the CRC, you can either check that the
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* CRC matches the recomputed value, *or* you can check that the
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* remainder computed on the message+CRC is 0. This latter approach
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* is used by a lot of hardware implementations, and is why so many
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* protocols put the end-of-frame flag after the CRC.
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*
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* It's actually the same long division you learned in school, except that
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* - We're working in binary, so the digits are only 0 and 1, and
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* - When dividing polynomials, there are no carries. Rather than add and
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* subtract, we just xor. Thus, we tend to get a bit sloppy about
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* the difference between adding and subtracting.
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*
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* A 32-bit CRC polynomial is actually 33 bits long. But since it's
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* 33 bits long, bit 32 is always going to be set, so usually the CRC
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* is written in hex with the most significant bit omitted. (If you're
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* familiar with the IEEE 754 floating-point format, it's the same idea.)
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*
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* Note that a CRC is computed over a string of *bits*, so you have
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* to decide on the endianness of the bits within each byte. To get
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* the best error-detecting properties, this should correspond to the
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* order they're actually sent. For example, standard RS-232 serial is
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* little-endian; the most significant bit (sometimes used for parity)
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* is sent last. And when appending a CRC word to a message, you should
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* do it in the right order, matching the endianness.
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*
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* Just like with ordinary division, the remainder is always smaller than
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* the divisor (the CRC polynomial) you're dividing by. Each step of the
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* division, you take one more digit (bit) of the dividend and append it
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* to the current remainder. Then you figure out the appropriate multiple
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* of the divisor to subtract to being the remainder back into range.
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* In binary, it's easy - it has to be either 0 or 1, and to make the
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* XOR cancel, it's just a copy of bit 32 of the remainder.
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*
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* When computing a CRC, we don't care about the quotient, so we can
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* throw the quotient bit away, but subtract the appropriate multiple of
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* the polynomial from the remainder and we're back to where we started,
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* ready to process the next bit.
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*
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* A big-endian CRC written this way would be coded like:
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* for (i = 0; i < input_bits; i++) {
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* multiple = remainder & 0x80000000 ? CRCPOLY : 0;
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* remainder = (remainder << 1 | next_input_bit()) ^ multiple;
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* }
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* Notice how, to get at bit 32 of the shifted remainder, we look
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* at bit 31 of the remainder *before* shifting it.
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*
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* But also notice how the next_input_bit() bits we're shifting into
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* the remainder don't actually affect any decision-making until
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* 32 bits later. Thus, the first 32 cycles of this are pretty boring.
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* Also, to add the CRC to a message, we need a 32-bit-long hole for it at
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* the end, so we have to add 32 extra cycles shifting in zeros at the
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* end of every message,
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*
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* So the standard trick is to rearrage merging in the next_input_bit()
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* until the moment it's needed. Then the first 32 cycles can be precomputed,
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* and merging in the final 32 zero bits to make room for the CRC can be
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* skipped entirely.
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* This changes the code to:
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* for (i = 0; i < input_bits; i++) {
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* remainder ^= next_input_bit() << 31;
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* multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
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* remainder = (remainder << 1) ^ multiple;
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* }
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* With this optimization, the little-endian code is simpler:
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* for (i = 0; i < input_bits; i++) {
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* remainder ^= next_input_bit();
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* multiple = (remainder & 1) ? CRCPOLY : 0;
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* remainder = (remainder >> 1) ^ multiple;
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* }
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*
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* Note that the other details of endianness have been hidden in CRCPOLY
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* (which must be bit-reversed) and next_input_bit().
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*
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* However, as long as next_input_bit is returning the bits in a sensible
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* order, we can actually do the merging 8 or more bits at a time rather
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* than one bit at a time:
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* for (i = 0; i < input_bytes; i++) {
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* remainder ^= next_input_byte() << 24;
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* for (j = 0; j < 8; j++) {
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* multiple = (remainder & 0x80000000) ? CRCPOLY : 0;
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* remainder = (remainder << 1) ^ multiple;
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* }
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* }
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* Or in little-endian:
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* for (i = 0; i < input_bytes; i++) {
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* remainder ^= next_input_byte();
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* for (j = 0; j < 8; j++) {
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* multiple = (remainder & 1) ? CRCPOLY : 0;
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* remainder = (remainder << 1) ^ multiple;
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* }
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* }
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* If the input is a multiple of 32 bits, you can even XOR in a 32-bit
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* word at a time and increase the inner loop count to 32.
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*
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* You can also mix and match the two loop styles, for example doing the
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* bulk of a message byte-at-a-time and adding bit-at-a-time processing
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* for any fractional bytes at the end.
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*
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* The only remaining optimization is to the byte-at-a-time table method.
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* Here, rather than just shifting one bit of the remainder to decide
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* in the correct multiple to subtract, we can shift a byte at a time.
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* This produces a 40-bit (rather than a 33-bit) intermediate remainder,
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* but again the multiple of the polynomial to subtract depends only on
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* the high bits, the high 8 bits in this case.
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*
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* The multiple we need in that case is the low 32 bits of a 40-bit
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* value whose high 8 bits are given, and which is a multiple of the
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* generator polynomial. This is simply the CRC-32 of the given
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* one-byte message.
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*
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* Two more details: normally, appending zero bits to a message which
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* is already a multiple of a polynomial produces a larger multiple of that
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* polynomial. To enable a CRC to detect this condition, it's common to
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* invert the CRC before appending it. This makes the remainder of the
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* message+crc come out not as zero, but some fixed non-zero value.
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*
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* The same problem applies to zero bits prepended to the message, and
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* a similar solution is used. Instead of starting with a remainder of
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* 0, an initial remainder of all ones is used. As long as you start
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* the same way on decoding, it doesn't make a difference.
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*/
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#ifdef UNITTEST
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#include <stdlib.h>
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#include <stdio.h>
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#if 0 /*Not used at present */
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static void
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buf_dump(char const *prefix, unsigned char const *buf, size_t len)
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{
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fputs(prefix, stdout);
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while (len--)
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printf(" %02x", *buf++);
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putchar('\n');
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}
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#endif
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static void bytereverse(unsigned char *buf, size_t len)
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{
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while (len--) {
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unsigned char x = bitrev8(*buf);
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*buf++ = x;
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}
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}
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static void random_garbage(unsigned char *buf, size_t len)
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{
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while (len--)
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*buf++ = (unsigned char) random();
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}
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#if 0 /* Not used at present */
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static void store_le(u32 x, unsigned char *buf)
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{
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buf[0] = (unsigned char) x;
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buf[1] = (unsigned char) (x >> 8);
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buf[2] = (unsigned char) (x >> 16);
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buf[3] = (unsigned char) (x >> 24);
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}
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#endif
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static void store_be(u32 x, unsigned char *buf)
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{
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buf[0] = (unsigned char) (x >> 24);
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buf[1] = (unsigned char) (x >> 16);
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buf[2] = (unsigned char) (x >> 8);
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buf[3] = (unsigned char) x;
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}
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/*
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* This checks that CRC(buf + CRC(buf)) = 0, and that
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* CRC commutes with bit-reversal. This has the side effect
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* of bytewise bit-reversing the input buffer, and returns
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* the CRC of the reversed buffer.
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*/
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static u32 test_step(u32 init, unsigned char *buf, size_t len)
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{
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u32 crc1, crc2;
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size_t i;
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crc1 = crc32_be(init, buf, len);
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store_be(crc1, buf + len);
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crc2 = crc32_be(init, buf, len + 4);
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if (crc2)
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printf("\nCRC cancellation fail: 0x%08x should be 0\n",
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crc2);
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for (i = 0; i <= len + 4; i++) {
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crc2 = crc32_be(init, buf, i);
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crc2 = crc32_be(crc2, buf + i, len + 4 - i);
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if (crc2)
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printf("\nCRC split fail: 0x%08x\n", crc2);
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}
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/* Now swap it around for the other test */
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bytereverse(buf, len + 4);
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init = bitrev32(init);
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crc2 = bitrev32(crc1);
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if (crc1 != bitrev32(crc2))
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printf("\nBit reversal fail: 0x%08x -> 0x%08x -> 0x%08x\n",
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crc1, crc2, bitrev32(crc2));
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crc1 = crc32_le(init, buf, len);
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if (crc1 != crc2)
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printf("\nCRC endianness fail: 0x%08x != 0x%08x\n", crc1,
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crc2);
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crc2 = crc32_le(init, buf, len + 4);
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if (crc2)
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printf("\nCRC cancellation fail: 0x%08x should be 0\n",
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crc2);
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for (i = 0; i <= len + 4; i++) {
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crc2 = crc32_le(init, buf, i);
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crc2 = crc32_le(crc2, buf + i, len + 4 - i);
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if (crc2)
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printf("\nCRC split fail: 0x%08x\n", crc2);
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}
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return crc1;
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}
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#define SIZE 64
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#define INIT1 0
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#define INIT2 0
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int main(void)
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{
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unsigned char buf1[SIZE + 4];
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unsigned char buf2[SIZE + 4];
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unsigned char buf3[SIZE + 4];
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int i, j;
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u32 crc1, crc2, crc3;
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for (i = 0; i <= SIZE; i++) {
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printf("\rTesting length %d...", i);
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fflush(stdout);
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random_garbage(buf1, i);
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random_garbage(buf2, i);
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for (j = 0; j < i; j++)
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buf3[j] = buf1[j] ^ buf2[j];
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crc1 = test_step(INIT1, buf1, i);
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crc2 = test_step(INIT2, buf2, i);
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/* Now check that CRC(buf1 ^ buf2) = CRC(buf1) ^ CRC(buf2) */
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crc3 = test_step(INIT1 ^ INIT2, buf3, i);
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if (crc3 != (crc1 ^ crc2))
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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 */
|