[PATCH v4 2/4] hash: optimize compare signature for NEON

[Yoan Picchi <yoan.picchi@arm.com>]

Upon a successful comparison, NEON sets all the bits in the lane to 1
We can skip shifting by simply masking with specific masks.

Signed-off-by: Yoan Picchi <yoan.picchi@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Nathan Brown <nathan.brown@arm.com>
---
 lib/hash/rte_cuckoo_hash.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/lib/hash/rte_cuckoo_hash.c b/lib/hash/rte_cuckoo_hash.c
index 0550165584..a07dd3a28d 100644
--- a/lib/hash/rte_cuckoo_hash.c
+++ b/lib/hash/rte_cuckoo_hash.c
@@ -1871,19 +1871,17 @@ compare_signatures_dense(uint32_t *prim_hash_matches, uint32_t *sec_hash_matches
 	/* For match mask every bits indicates the match */
 	switch (sig_cmp_fn) {
 	case RTE_HASH_COMPARE_NEON: {
-		uint16x8_t vmat, vsig, x;
-		int16x8_t shift = {0, 1, 2, 3, 4, 5, 6, 7};
+		uint16x8_t vmat, x;
+		const uint16x8_t mask = {0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80};
+		const uint16x8_t vsig = vld1q_dup_u16((uint16_t const *)&sig);
 
-		vsig = vld1q_dup_u16((uint16_t const *)&sig);
 		/* Compare all signatures in the primary bucket */
-		vmat = vceqq_u16(vsig,
-			vld1q_u16((uint16_t const *)prim_bkt->sig_current));
-		x = vshlq_u16(vandq_u16(vmat, vdupq_n_u16(0x0001)), shift);
+		vmat = vceqq_u16(vsig, vld1q_u16((uint16_t const *)prim_bkt->sig_current));
+		x = vandq_u16(vmat, mask);
 		*prim_hash_matches = (uint32_t)(vaddvq_u16(x));
 		/* Compare all signatures in the secondary bucket */
-		vmat = vceqq_u16(vsig,
-			vld1q_u16((uint16_t const *)sec_bkt->sig_current));
-		x = vshlq_u16(vandq_u16(vmat, vdupq_n_u16(0x0001)), shift);
+		vmat = vceqq_u16(vsig, vld1q_u16((uint16_t const *)sec_bkt->sig_current));
+		x = vandq_u16(vmat, mask);
 		*sec_hash_matches = (uint32_t)(vaddvq_u16(x));
 		}
 		break;
-- 
2.25.1