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 <redacted>
Acked-by: David Marchand <redacted>

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