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 <pbhagavatula@marvell.com>

diff --git a/lib/librte_eal/common/rte_reciprocal.c b/lib/librte_eal/common/rte_reciprocal.c
index f017d0c..1c6d10e 100644 (file)
--- 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;