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| author | Eric Biggers <ebiggers@kernel.org> | 2025-06-06 20:22:28 -0700 |
|---|---|---|
| committer | Eric Biggers <ebiggers@kernel.org> | 2025-06-30 09:31:57 -0700 |
| commit | f2703a104e89077e622e2f34ac686262c5180d71 (patch) | |
| tree | 4886a3c868496d465dac7f53f9b1c91d90823b08 /lib/crc32.c | |
| parent | b0e04dde8e78fd0f08210c594ab29cbbcd841b73 (diff) | |
| download | net-f2703a104e89077e622e2f34ac686262c5180d71.tar.gz | |
lib/crc32: Remove unused combination support
Remove crc32_le_combine() and crc32_le_shift(), since they are no longer
used.
Although combination is an interesting thing that can be done with CRCs,
it turned out that none of the users of it in the kernel were even close
to being worthwhile. All were much better off simply chaining the CRCs
or processing zeroes.
Let's remove the CRC32 combination code for now. It can come back
(potentially optimized with carryless multiplication instructions) if
there is ever a case where it would actually be worthwhile.
Link: https://lore.kernel.org/r/20250607032228.27868-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Diffstat (limited to 'lib/crc32.c')
| -rw-r--r-- | lib/crc32.c | 67 |
1 files changed, 0 insertions, 67 deletions
diff --git a/lib/crc32.c b/lib/crc32.c index 95429861d3aca2..6811b37df2aada 100644 --- a/lib/crc32.c +++ b/lib/crc32.c @@ -25,7 +25,6 @@ /* 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> @@ -51,72 +50,6 @@ u32 crc32c_base(u32 crc, const u8 *p, size_t len) } EXPORT_SYMBOL(crc32c_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 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 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 crc32_le_shift(u32 crc, size_t len) -{ - return crc32_generic_shift(crc, len, CRC32_POLY_LE); -} -EXPORT_SYMBOL(crc32_le_shift); - u32 crc32_be_base(u32 crc, const u8 *p, size_t len) { while (len--) |