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/*
* Aug 8, 2011 Bob Pearson with help from Joakim Tjernlund and George Spelvin
* cleaned up code to current version of sparse and added the slicing-by-8
* algorithm to the closely similar existing slicing-by-4 algorithm.
*
* 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.
*/
/* see: Documentation/staging/crc32.rst for a description of algorithms */
#include <linux/crc32.h>
#include <linux/crc32poly.h>
#include <linux/module.h>
#include <linux/types.h>
#include "crc32table.h"
MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
MODULE_DESCRIPTION("Various CRC32 calculations");
MODULE_LICENSE("GPL");
u32 __pure crc32_le_base(u32 crc, const u8 *p, size_t len)
{
while (len--)
crc = (crc >> 8) ^ crc32table_le[(crc & 255) ^ *p++];
return crc;
}
EXPORT_SYMBOL(crc32_le_base);
u32 __pure crc32c_le_base(u32 crc, const u8 *p, size_t len)
{
while (len--)
crc = (crc >> 8) ^ crc32ctable_le[(crc & 255) ^ *p++];
return crc;
}
EXPORT_SYMBOL(crc32c_le_base);
/*
* This multiplies the polynomials x and y modulo the given modulus.
* This follows the "little-endian" CRC convention that the lsbit
* represents the highest power of x, and the msbit represents x^0.
*/
static u32 __attribute_const__ gf2_multiply(u32 x, u32 y, u32 modulus)
{
u32 product = x & 1 ? y : 0;
int i;
for (i = 0; i < 31; i++) {
product = (product >> 1) ^ (product & 1 ? modulus : 0);
x >>= 1;
product ^= x & 1 ? y : 0;
}
return product;
}
/**
* crc32_generic_shift - Append @len 0 bytes to crc, in logarithmic time
* @crc: The original little-endian CRC (i.e. lsbit is x^31 coefficient)
* @len: The number of bytes. @crc is multiplied by x^(8*@len)
* @polynomial: The modulus used to reduce the result to 32 bits.
*
* It's possible to parallelize CRC computations by computing a CRC
* over separate ranges of a buffer, then summing them.
* This shifts the given CRC by 8*len bits (i.e. produces the same effect
* as appending len bytes of zero to the data), in time proportional
* to log(len).
*/
static u32 __attribute_const__ crc32_generic_shift(u32 crc, size_t len,
u32 polynomial)
{
u32 power = polynomial; /* CRC of x^32 */
int i;
/* Shift up to 32 bits in the simple linear way */
for (i = 0; i < 8 * (int)(len & 3); i++)
crc = (crc >> 1) ^ (crc & 1 ? polynomial : 0);
len >>= 2;
if (!len)
return crc;
for (;;) {
/* "power" is x^(2^i), modulo the polynomial */
if (len & 1)
crc = gf2_multiply(crc, power, polynomial);
len >>= 1;
if (!len)
break;
/* Square power, advancing to x^(2^(i+1)) */
power = gf2_multiply(power, power, polynomial);
}
return crc;
}
u32 __attribute_const__ crc32_le_shift(u32 crc, size_t len)
{
return crc32_generic_shift(crc, len, CRC32_POLY_LE);
}
u32 __attribute_const__ __crc32c_le_shift(u32 crc, size_t len)
{
return crc32_generic_shift(crc, len, CRC32C_POLY_LE);
}
EXPORT_SYMBOL(crc32_le_shift);
EXPORT_SYMBOL(__crc32c_le_shift);
u32 __pure crc32_be_base(u32 crc, const u8 *p, size_t len)
{
while (len--)
crc = (crc << 8) ^ crc32table_be[(crc >> 24) ^ *p++];
return crc;
}
EXPORT_SYMBOL(crc32_be_base);
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