On 2015-03-18 17:51, Yerden Zhumabekov wrote:
> Fix rte_hash_crc() function. Casting uint64_t pointer to uin32_t
> may trigger a compiler warning about breaking strict-aliasing rules.
> To avoid that, introduce a lookup table which is used to mask out
> a remainder of data.
>
> See issue #1, http://dpdk.org/ml/archives/dev/2015-March/015174.html
>
> Signed-off-by: Yerden Zhumabekov <e_zhumabekov at sts.kz>
> ---
> lib/librte_hash/rte_hash_crc.h | 31 +++++++++++++++----------------
> 1 file changed, 15 insertions(+), 16 deletions(-)
>
> diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
> index 3dcd362..e81920f 100644
> --- a/lib/librte_hash/rte_hash_crc.h
> +++ b/lib/librte_hash/rte_hash_crc.h
> @@ -323,6 +323,16 @@ static const uint32_t crc32c_tables[8][256] = {{
> 0xE54C35A1, 0xAC704886, 0x7734CFEF, 0x3E08B2C8, 0xC451B7CC, 0x8D6DCAEB,
> 0x56294D82, 0x1F1530A5
> }};
>
> +static const uint64_t odd_8byte_mask[] = {
> + 0x00FFFFFFFFFFFFFF,
> + 0x0000FFFFFFFFFFFF,
> + 0x000000FFFFFFFFFF,
> + 0x00000000FFFFFFFF,
> + 0x0000000000FFFFFF,
> + 0x000000000000FFFF,
> + 0x00000000000000FF,
> +};
> +
> #define CRC32_UPD(crc, n) \
> (crc32c_tables[(n)][(crc) & 0xFF] ^ \
> crc32c_tables[(n)-1][((crc) >> 8) & 0xFF])
> @@ -535,38 +545,27 @@ static inline uint32_t
> rte_hash_crc(const void *data, uint32_t data_len, uint32_t init_val)
> {
> unsigned i;
> - uint64_t temp = 0;
> + uint64_t temp;
> const uint64_t *p64 = (const uint64_t *)data;
>
> for (i = 0; i < data_len / 8; i++) {
> init_val = rte_hash_crc_8byte(*p64++, init_val);
> }
>
> - switch (7 - (data_len & 0x07)) {
> + i = 7 - (data_len & 0x07);
Great idea with lookup table!
Only one question here: why keeping this magic at all now?
If you sort odd_8byte_mask opposite direction you can do something like that
data_len &= 0x07;
switch (data_len & 0x07) {
case 1:
case 2:
case 3:
case 4:
temp = odd_8byte_mask[data_len] & *p64;
init_val = rte_hash_crc_4byte(temp, init_val);
case 5:
case 6:
case 7:
temp = odd_8byte_mask[data_len] & *p64;
init_val = rte_hash_crc_8byte(temp, init_val);
break;
default:
break;
}
Or
data_len &= 0x07;
if (data_len > 0) {
temp = odd_8byte_mask[data_len] & *p64;
if (data_len <= 4)
init_val = rte_hash_crc_4byte(temp, init_val);
else
init_val = rte_hash_crc_8byte(temp, init_val);
}
Is there something obvious what I am not seeing here?
Pawel
> + switch (i) {
> case 0:
> - temp |= (uint64_t) *((const uint8_t *)p64 + 6) << 48;
> - /* Fallthrough */
> case 1:
> - temp |= (uint64_t) *((const uint8_t *)p64 + 5) << 40;
> - /* Fallthrough */
> case 2:
> - temp |= (uint64_t) *((const uint8_t *)p64 + 4) << 32;
> - temp |= *((const uint32_t *)p64);
> + temp = odd_8byte_mask[i] & *p64;
> init_val = rte_hash_crc_8byte(temp, init_val);
> break;
> case 3:
> - init_val = rte_hash_crc_4byte(*(const uint32_t *)p64, init_val);
> - break;
> case 4:
> - temp |= *((const uint8_t *)p64 + 2) << 16;
> - /* Fallthrough */
> case 5:
> - temp |= *((const uint8_t *)p64 + 1) << 8;
> - /* Fallthrough */
> case 6:
> - temp |= *((const uint8_t *)p64);
> + temp = odd_8byte_mask[i] & *p64;
> init_val = rte_hash_crc_4byte(temp, init_val);
> - /* Fallthrough */
> default:
> break;
> }
>
--
Pawel
