[dpdk-stable] [dpdk-dev] [PATCH] eal/reciprocal: fix off by one when divisor is 32bit

[pbhagavatula at marvell.com]

From: Pavan Nikhilesh <pbhagavatula at marvell.com>

Fix off by one error in 64bit reciprocal division when divisor is 32bit.

Fixes: 6d45659eacb8 ("eal: add u64-bit variant for reciprocal divide")
Cc: stable at dpdk.org

Signed-off-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
---

Example:
   Division failed, 17358247066007716387/244 =
   		expected 71140356827900476 result 71140356827900477
   Division failed, 17541123788887206374/41475 =
   		expected 422932460250444 result 422932460250445

 lib/librte_eal/common/rte_reciprocal.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/librte_eal/common/rte_reciprocal.c b/lib/librte_eal/common/rte_reciprocal.c
index f017d0c28..1c6d10e73 100644
--- a/lib/librte_eal/common/rte_reciprocal.c
+++ b/lib/librte_eal/common/rte_reciprocal.c
@@ -133,12 +133,15 @@ rte_reciprocal_value_u64(uint64_t d)
 {
 	struct rte_reciprocal_u64 R;
 	uint64_t m;
+	uint64_t r;
 	int l;

 	l = 63 - __builtin_clzll(d);

-	m = divide_128_div_64_to_64((1ULL << l), 0, d, NULL) << 1;
-	m = (1ULL << l) - d ? m + 2 : 1;
+	m = divide_128_div_64_to_64((1ULL << l), 0, d, &r) << 1;
+	if (r << 1 < r || r << 1 >= d)
+		m++;
+	m = (1ULL << l) - d ? m + 1 : 1;
 	R.m = m;

 	R.sh1 = l > 1 ? 1 : l;
--
2.23.0