[dpdk-dev] [PATCH v3 3/5] common: add missing implementations

[Anatoly Burakov]

Implement missing functions for 32-bit safe bsf, as well as 64-bit
fls and log2.

Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu at intel.com>
---

Notes:
    v3:
    - Added clarification that pos is not checked

 lib/librte_eal/common/include/rte_common.h | 64 +++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
index d115b175c..6883e5c3b 100644
--- a/lib/librte_eal/common/include/rte_common.h
+++ b/lib/librte_eal/common/include/rte_common.h
@@ -456,6 +456,30 @@ rte_bsf32(uint32_t v)
 	return (uint32_t)__builtin_ctz(v);
 }
 
+/**
+ * Searches the input parameter for the least significant set bit
+ * (starting from zero). Safe version (checks for input parameter being zero).
+ *
+ * @warning ``pos`` must be a valid pointer. It is not checked!
+ *
+ * @param v
+ *     The input parameter.
+ * @param pos
+ *     If ``v`` was not 0, this value will contain position of least significant
+ *     bit within the input parameter.
+ * @return
+ *     Returns 0 if ``v`` was 0, otherwise returns 1.
+ */
+static inline int
+rte_bsf32_safe(uint64_t v, uint32_t *pos)
+{
+	if (v == 0)
+		return 0;
+
+	*pos = rte_bsf32(v);
+	return 1;
+}
+
 /**
  * Return the rounded-up log2 of a integer.
  *
@@ -473,7 +497,6 @@ rte_log2_u32(uint32_t v)
 	return rte_bsf32(v);
 }
 
-
 /**
  * Return the last (most-significant) bit set.
  *
@@ -515,6 +538,45 @@ rte_bsf64_safe(uint64_t v, uint32_t *pos)
 	return 1;
 }
 
+/**
+ * Return the last (most-significant) bit set.
+ *
+ * @note The last (most significant) bit is at position 32.
+ * @note rte_fls_u32(0) = 0, rte_fls_u32(1) = 1, rte_fls_u32(0x80000000) = 32
+ *
+ * @param x
+ *     The input parameter.
+ * @return
+ *     The last (most-significant) bit set, or 0 if the input is 0.
+ */
+static inline int
+rte_fls_u64(uint64_t x)
+{
+	return (x == 0) ? 0 : 64 - __builtin_clzll(x);
+}
+
+/**
+ * Return the rounded-up log2 of a integer.
+ *
+ * @param v
+ *     The input parameter.
+ * @return
+ *     The rounded-up log2 of the input, or 0 if the input is 0.
+ */
+static inline uint32_t
+rte_log2_u64(uint64_t v)
+{
+	uint32_t pos = 0;
+	if (v == 0)
+		return 0;
+	v = rte_align64pow2(v);
+	/* TODO: replace with rte_bsf64 when that lands */
+	/* we checked for v being 0 already, so pos is always valid */
+	rte_bsf64_safe(v, &pos);
+	return pos;
+}
+
+
 #ifndef offsetof
 /** Return the offset of a field in a structure. */
 #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)
-- 
2.17.1