[dpdk-stable] [PATCH v2] test/common: fix log2 check

[David Marchand]

We recently started to get random failures on the common_autotest ut with
clang on Ubuntu 16.04.6.

Example: https://travis-ci.com/DPDK/dpdk/jobs/263177424

Wrong rte_log2_u64(0) val 0, expected ffffffff
Test Failed

The ut passes 0 to log2() to get an expected value.

Quoting log2 / log(3) manual:
If x is zero, then a pole error occurs, and the functions return
-HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

rte_log2_uXX helpers handle 0 as a special value and return 0.
Let's have dedicated tests for this case.

Fixes: 05c4345ef5c2 ("test: add unit test for integer log2 function")
Cc: stable at dpdk.org

Signed-off-by: David Marchand <david.marchand at redhat.com>
Acked-by: Aaron Conole <aconole at redhat.com>
---
Changelog since v1:
- added comment in rte_log2_uXX API descriptions,

---
 app/test/test_common.c                     | 14 +++++++++++++-
 lib/librte_eal/common/include/rte_common.h |  6 ++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/app/test/test_common.c b/app/test/test_common.c
index 2b856f8ba5..12bd1cad90 100644
--- a/app/test/test_common.c
+++ b/app/test/test_common.c
@@ -216,7 +216,19 @@ test_log2(void)
 	const uint32_t max = 0x10000;
 	const uint32_t step = 1;
 
-	for (i = 0; i < max; i = i + step) {
+	compare = rte_log2_u32(0);
+	if (compare != 0) {
+		printf("Wrong rte_log2_u32(0) val %x, expected 0\n", compare);
+		return TEST_FAILED;
+	}
+
+	compare = rte_log2_u64(0);
+	if (compare != 0) {
+		printf("Wrong rte_log2_u64(0) val %x, expected 0\n", compare);
+		return TEST_FAILED;
+	}
+
+	for (i = 1; i < max; i = i + step) {
 		uint64_t i64;
 
 		/* extend range for 64-bit */
diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
index 459d082d14..7a98071ffe 100644
--- a/lib/librte_eal/common/include/rte_common.h
+++ b/lib/librte_eal/common/include/rte_common.h
@@ -538,6 +538,9 @@ rte_bsf32_safe(uint64_t v, uint32_t *pos)
 /**
  * Return the rounded-up log2 of a integer.
  *
+ * @note Contrary to the logarithm mathematical operation,
+ * rte_log2_u32(0) == 0 and not -inf.
+ *
  * @param v
  *     The input parameter.
  * @return
@@ -632,6 +635,9 @@ rte_fls_u64(uint64_t x)
 /**
  * Return the rounded-up log2 of a 64-bit integer.
  *
+ * @note Contrary to the logarithm mathematical operation,
+ * rte_log2_u32(0) == 0 and not -inf.
+ *
  * @param v
  *     The input parameter.
  * @return
-- 
2.23.0