[dpdk-dev] [PATCH v2 1/2] eal: add API to align integer to previous power of 2

[Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>]

Add 32b and 64b API's to align the given integer to the previous power
of 2.

Signed-off-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>
---
 v2 Changes:
 - Modified api name to `rte_align(32/64)prevpow2` from
 `rte_align(32/64)lowpow2`.
 - corrected fuction to return if the integer is already aligned to
 power of 2.

 lib/librte_eal/common/include/rte_common.h | 43 ++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
index c7803e41c..b2017ee5c 100644
--- a/lib/librte_eal/common/include/rte_common.h
+++ b/lib/librte_eal/common/include/rte_common.h
@@ -259,6 +259,27 @@ rte_align32pow2(uint32_t x)
 	return x + 1;
 }

+/**
+ * Aligns input parameter to the previous power of 2
+ *
+ * @param x
+ *   The integer value to algin
+ *
+ * @return
+ *   Input parameter aligned to the previous power of 2
+ */
+static inline uint32_t
+rte_align32prevpow2(uint32_t x)
+{
+	x |= x >> 1;
+	x |= x >> 2;
+	x |= x >> 4;
+	x |= x >> 8;
+	x |= x >> 16;
+
+	return x - (x >> 1);
+}
+
 /**
  * Aligns 64b input parameter to the next power of 2
  *
@@ -282,6 +303,28 @@ rte_align64pow2(uint64_t v)
 	return v + 1;
 }

+/**
+ * Aligns 64b input parameter to the previous power of 2
+ *
+ * @param v
+ *   The 64b value to align
+ *
+ * @return
+ *   Input parameter aligned to the previous power of 2
+ */
+static inline uint64_t
+rte_align64prevpow2(uint64_t v)
+{
+	v |= v >> 1;
+	v |= v >> 2;
+	v |= v >> 4;
+	v |= v >> 8;
+	v |= v >> 16;
+	v |= v >> 32;
+
+	return v - (v >> 1);
+}
+
 /*********** Macros for calculating min and max **********/

 /**
--
2.16.1