lib/crc32: remove unused support for CRC32C combination

crc32c_combine() and crc32c_shift() are no longer used (except by the
KUnit test that tests them), and their current implementation is very
slow.  Remove them.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://patch.msgid.link/20250519175012.36581-8-ebiggers@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: ebiggers

include/linux/crc32.h

@@ -76,29 +76,6 @@ static inline u32 crc32_le_combine(u32 crc1, u32 crc2, size_t len2)
 	return crc32_le_shift(crc1, len2) ^ crc2;
 }
 
-u32 crc32c_shift(u32 crc, size_t len);
-
-/**
- * crc32c_combine - Combine two crc32c check values into one. For two sequences
- *		    of bytes, seq1 and seq2 with lengths len1 and len2, crc32c()
- *		    check values were calculated for each, crc1 and crc2.
- *
- * @crc1: crc32c of the first block
- * @crc2: crc32c of the second block
- * @len2: length of the second block
- *
- * Return: The crc32c() check value of seq1 and seq2 concatenated, requiring
- *	   only crc1, crc2, and len2. Note: If seq_full denotes the concatenated
- *	   memory area of seq1 with seq2, and crc_full the crc32c() value of
- *	   seq_full, then crc_full == crc32c_combine(crc1, crc2, len2) when
- *	   crc_full was seeded with the same initializer as crc1, and crc2 seed
- *	   was 0. See also crc_combine_test().
- */
-static inline u32 crc32c_combine(u32 crc1, u32 crc2, size_t len2)
-{
-	return crc32c_shift(crc1, len2) ^ crc2;
-}
-
 #define crc32(seed, data, length)  crc32_le(seed, (unsigned char const *)(data), length)
 
 /*

lib/crc32.c

@@ -119,12 +119,6 @@ u32 crc32_le_shift(u32 crc, size_t len)
 }
 EXPORT_SYMBOL(crc32_le_shift);
 
-u32 crc32c_shift(u32 crc, size_t len)
-{
-	return crc32_generic_shift(crc, len, CRC32C_POLY_LE);
-}
-EXPORT_SYMBOL(crc32c_shift);
-
 u32 crc32_be_base(u32 crc, const u8 *p, size_t len)
 {
 	while (len--)

lib/tests/crc_kunit.c

@@ -391,17 +391,11 @@ static u64 crc32c_wrapper(u64 crc, const u8 *p, size_t len)
 	return crc32c(crc, p, len);
 }
 
-static u64 crc32c_combine_wrapper(u64 crc1, u64 crc2, size_t len2)
-{
-	return crc32c_combine(crc1, crc2, len2);
-}
-
 static const struct crc_variant crc_variant_crc32c = {
 	.bits = 32,
 	.le = true,
 	.poly = 0x82f63b78,
 	.func = crc32c_wrapper,
-	.combine_func = crc32c_combine_wrapper,
 };
 
 static void crc32c_test(struct kunit *test)