diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Kconfig | 8 | ||||
| -rw-r--r-- | lib/Makefile | 1 | ||||
| -rw-r--r-- | lib/crc4.c | 46 |
3 files changed, 55 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig index 0c8b78a9ae2e..d2fd2623721e 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -158,6 +158,14 @@ config CRC32_BIT endchoice +config CRC4 + tristate "CRC4 functions" + help + This option is provided for the case where no in-kernel-tree + modules require CRC4 functions, but a module built outside + the kernel tree does. Such modules that use library CRC4 + functions require M here. + config CRC7 tristate "CRC7 functions" help diff --git a/lib/Makefile b/lib/Makefile index 0166fbc0fa81..90cf124e5feb 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -99,6 +99,7 @@ obj-$(CONFIG_CRC_T10DIF)+= crc-t10dif.o obj-$(CONFIG_CRC_ITU_T) += crc-itu-t.o obj-$(CONFIG_CRC32) += crc32.o obj-$(CONFIG_CRC32_SELFTEST) += crc32test.o +obj-$(CONFIG_CRC4) += crc4.o obj-$(CONFIG_CRC7) += crc7.o obj-$(CONFIG_LIBCRC32C) += libcrc32c.o obj-$(CONFIG_CRC8) += crc8.o diff --git a/lib/crc4.c b/lib/crc4.c new file mode 100644 index 000000000000..cf6db46661be --- /dev/null +++ b/lib/crc4.c @@ -0,0 +1,46 @@ +/* + * crc4.c - simple crc-4 calculations. + * + * This source code is licensed under the GNU General Public License, Version + * 2. See the file COPYING for more details. + */ + +#include <linux/crc4.h> +#include <linux/module.h> + +static const uint8_t crc4_tab[] = { + 0x0, 0x7, 0xe, 0x9, 0xb, 0xc, 0x5, 0x2, + 0x1, 0x6, 0xf, 0x8, 0xa, 0xd, 0x4, 0x3, +}; + +/** + * crc4 - calculate the 4-bit crc of a value. + * @crc: starting crc4 + * @x: value to checksum + * @bits: number of bits in @x to checksum + * + * Returns the crc4 value of @x, using polynomial 0b10111. + * + * The @x value is treated as left-aligned, and bits above @bits are ignored + * in the crc calculations. + */ +uint8_t crc4(uint8_t c, uint64_t x, int bits) +{ + int i; + + /* mask off anything above the top bit */ + x &= (1ull << bits) - 1; + + /* Align to 4-bits */ + bits = (bits + 3) & ~0x3; + + /* Calculate crc4 over four-bit nibbles, starting at the MSbit */ + for (i = bits - 4; i >= 0; i -= 4) + c = crc4_tab[c ^ ((x >> i) & 0xf)]; + + return c; +} +EXPORT_SYMBOL_GPL(crc4); + +MODULE_DESCRIPTION("CRC4 calculations"); +MODULE_LICENSE("GPL"); |