[PATCH] hash: fix SSE comparison

[Jieqiang Wang]

__mm_cmpeq_epi16 returns 0xFFFF if the corresponding 16-bit elements are
equal. In original SSE2 implementation for function compare_signatures,
it utilizes _mm_movemask_epi8 to create mask from the MSB of each 8-bit
element, while we should only care about the MSB of lower 8-bit in each
16-bit element.
For example, if the comparison result is all equal, SSE2 path returns
0xFFFF while NEON and default scalar path return 0x5555.
Although this bug is not causing any negative effects since the caller
function solely examines the trailing zeros of each match mask, we
recommend this fix to ensure consistency with NEON and default scalar
code behaviors.

Fixes: c7d93df552c2 ("hash: use partial-key hashing")
Cc: yipeng1.wang at intel.com
Cc: stable at dpdk.org

Signed-off-by: Feifei Wang <feifei.wang2 at arm.com>
Signed-off-by: Jieqiang Wang <jieqiang.wang at arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
---
 lib/hash/rte_cuckoo_hash.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/lib/hash/rte_cuckoo_hash.c b/lib/hash/rte_cuckoo_hash.c
index d92a903bb3..acaa8b74bd 100644
--- a/lib/hash/rte_cuckoo_hash.c
+++ b/lib/hash/rte_cuckoo_hash.c
@@ -1862,17 +1862,19 @@ compare_signatures(uint32_t *prim_hash_matches, uint32_t *sec_hash_matches,
 	/* For match mask the first bit of every two bits indicates the match */
 	switch (sig_cmp_fn) {
 #if defined(__SSE2__)
-	case RTE_HASH_COMPARE_SSE:
+	case RTE_HASH_COMPARE_SSE: {
 		/* Compare all signatures in the bucket */
-		*prim_hash_matches = _mm_movemask_epi8(_mm_cmpeq_epi16(
-				_mm_load_si128(
+		__m128i shift_mask = _mm_set1_epi16(0x0080);
+		__m128i prim_cmp = _mm_cmpeq_epi16(_mm_load_si128(
 					(__m128i const *)prim_bkt->sig_current),
-				_mm_set1_epi16(sig)));
+					_mm_set1_epi16(sig));
+		*prim_hash_matches = _mm_movemask_epi8(_mm_and_si128(prim_cmp, shift_mask));
 		/* Compare all signatures in the bucket */
-		*sec_hash_matches = _mm_movemask_epi8(_mm_cmpeq_epi16(
-				_mm_load_si128(
+		__m128i sec_cmp = _mm_cmpeq_epi16(_mm_load_si128(
 					(__m128i const *)sec_bkt->sig_current),
-				_mm_set1_epi16(sig)));
+					_mm_set1_epi16(sig));
+		*sec_hash_matches = _mm_movemask_epi8(_mm_and_si128(sec_cmp, shift_mask));
+		}
 		break;
 #elif defined(__ARM_NEON)
 	case RTE_HASH_COMPARE_NEON: {
-- 
2.25.1