From 9b0a1dadc345805ca9d7428a977da080d5eee7e2 Mon Sep 17 00:00:00 2001 From: Pavan Nikhilesh Date: Wed, 4 Sep 2019 00:46:45 +0530 Subject: [PATCH] reciprocal: fix off-by-one with 32-bit divisor Fix off-by-one error in 64bit reciprocal division when divisor is 32bit. Caught with the unit test: RTE>>reciprocal_division Validating unsigned 32bit division. Validating unsigned 64bit division. Validating unsigned 64bit division with 32bit divisor. Division failed, 16983222950483802557/819 = expected 20736535959076681 result 20736535959076682 Validating division by power of 2. Test Failed Fixes: 6d45659eacb8 ("eal: add u64-bit variant for reciprocal divide") Cc: stable@dpdk.org Signed-off-by: Pavan Nikhilesh --- 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 f017d0c283..1c6d10e733 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; -- 2.20.1