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reciprocal: fix off-by-one with 32-bit divisor

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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: 6d45659eac ("eal: add u64-bit variant for reciprocal divide")
Cc: stable@dpdk.org

Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
This commit is contained in:
Pavan Nikhilesh 2019-09-04 00:46:45 +05:30 committed by David Marchand
parent d170527643
commit 9b0a1dadc3
1 changed files with 5 additions and 2 deletions
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7
lib/librte_eal/common/rte_reciprocal.c
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@ -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;