Re: [dpdk-dev] [PATCH v2] hash: fix CRC32c computation

["De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>]

Hi Didier,

> -----Original Message-----
> From: Didier Pallard [mailto:didier.pallard@6wind.com]
> Sent: Tuesday, February 09, 2016 9:34 AM
> To: dev@dpdk.org; Richardson, Bruce; De Lara Guarch, Pablo
> Cc: jean-mickael.guerin@6wind.com; thomas.monjalon@6wind.com
> Subject: [PATCH v2] hash: fix CRC32c computation
> 
> As demonstrated by the following code, CRC32c computation is not valid
> when buffer length is not a multiple of 4 bytes:
> (Output obtained by code below)
> 
> CRC of 1 NULL bytes expected: 0x527d5351
>     soft: 527d5351
>     rte accelerated: 48674bc7
>     rte soft: 48674bc7
> CRC of 2 NULL bytes expected: 0xf16177d2
>     soft: f16177d2
>     rte accelerated: 48674bc7
>     rte soft: 48674bc7
> CRC of 2x1 NULL bytes expected: 0xf16177d2
>     soft: f16177d2
>     rte accelerated: 8c28b28a
>     rte soft: 8c28b28a
> CRC of 3 NULL bytes expected: 0x6064a37a
>     soft: 6064a37a
>     rte accelerated: 48674bc7
>     rte soft: 48674bc7
> CRC of 4 NULL bytes expected: 0x48674bc7
>     soft: 48674bc7
>     rte accelerated: 48674bc7
>     rte soft: 48674bc7
> 
> Values returned by rte_hash_crc functions does not match the one
> computed by a trivial crc32c implementation.
> 
> ARM code is not tested.
> 
> code showing the problem:
> 
> uint8_t null_test[32] = {0};
> 
> static uint32_t crc32c_trivial(uint8_t *buffer, uint32_t length, uint32_t crc)
> {
>     uint32_t i, j;
>     for (i = 0; i < length; ++i)
>     {
>         crc = crc ^ buffer[i];
>         for (j = 0; j < 8; j++)
>             crc = (crc >> 1) ^ 0x80000000 ^ ((~crc & 1) * 0x82f63b78);
>     }
>     return crc;
> }
> 
> void hash_test(void);
> void hash_test(void)
> {
> 	printf("CRC of 1 nul byte expected: 0x527d5351\n");
> 	printf("    soft: %08x\n", crc32c_trivial(null_test, 1, 0));
> 	rte_hash_crc_init_alg();
> 	printf("    rte accelerated: %08x\n", ~rte_hash_crc(null_test, 1,
> 0xFFFFFFFF));
> 	rte_hash_crc_set_alg(CRC32_SW);
> 	printf("    rte soft: %08x\n", ~rte_hash_crc(null_test, 1, 0xFFFFFFFF));
> 
> 	printf("CRC of 2 nul bytes expected: 0xf16177d2\n");
> 	printf("    soft: %08x\n", crc32c_trivial(null_test, 2, 0));
> 	rte_hash_crc_init_alg();
> 	printf("    rte accelerated: %08x\n", ~rte_hash_crc(null_test, 2,
> 0xFFFFFFFF));
> 	rte_hash_crc_set_alg(CRC32_SW);
> 	printf("    rte soft: %08x\n", ~rte_hash_crc(null_test, 2, 0xFFFFFFFF));
> 
> 	printf("CRC of 2x1 nul bytes expected: 0xf16177d2\n");
> 	printf("    soft: %08x\n", crc32c_trivial(null_test, 1,
> crc32c_trivial(null_test, 1, 0)));
> 	rte_hash_crc_init_alg();
> 	printf("    rte accelerated: %08x\n", ~rte_hash_crc(null_test, 1,
> rte_hash_crc(null_test, 1, 0xFFFFFFFF)));
> 	rte_hash_crc_set_alg(CRC32_SW);
> 	printf("    rte soft: %08x\n", ~rte_hash_crc(null_test, 1,
> rte_hash_crc(null_test, 1, 0xFFFFFFFF)));
> 
> 	printf("CRC of 3 nul bytes expected: 0x6064a37a\n");
> 	printf("    soft: %08x\n", crc32c_trivial(null_test, 3, 0));
> 	rte_hash_crc_init_alg();
> 	printf("    rte accelerated: %08x\n", ~rte_hash_crc(null_test, 3,
> 0xFFFFFFFF));
> 	rte_hash_crc_set_alg(CRC32_SW);
> 	printf("    rte soft: %08x\n", ~rte_hash_crc(null_test, 3, 0xFFFFFFFF));
> 
> 	printf("CRC of 4 nul bytes expected: 0x48674bc7\n");
> 	printf("    soft: %08x\n", crc32c_trivial(null_test, 4, 0));
> 	rte_hash_crc_init_alg();
> 	printf("    rte accelerated: %08x\n", ~rte_hash_crc(null_test, 4,
> 0xFFFFFFFF));
> 	rte_hash_crc_set_alg(CRC32_SW);
> 	printf("    rte soft: %08x\n", ~rte_hash_crc(null_test, 4, 0xFFFFFFFF));
> }
> 
> Signed-off-by: Didier Pallard <didier.pallard@6wind.com>
> Acked-by: David Marchand <david.marchand@6wind.com>

It compiles fine now, thanks!
Could you add also tests for not multiple of 4 bytes keys in test_hash_functions.c,
so we make sure from now on that it works (and you can demonstrate that your fix works)?
You could send a patchset with those new tests first and then the fix.

Also, a note in release notes would be welcome :)

Thanks!
Pablo