eal: add functions for previous power of 2 alignment

[dpdk.git] / lib / librte_eal / common / include / rte_common.h

diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
index 4469aff..6c5bc5a 100644 (file)
--- a/lib/librte_eal/common/include/rte_common.h
+++ b/lib/librte_eal/common/include/rte_common.h
@@ -239,6 +239,51 @@ extern int RTE_BUILD_BUG_ON_detected_error;
 } while(0)
 #endif
 
+/**
+ * Combines 32b inputs most significant set bits into the least
+ * significant bits to construct a value with the same MSBs as x
+ * but all 1's under it.
+ *
+ * @param x
+ *    The integer whose MSBs need to be combined with its LSBs
+ * @return
+ *    The combined value.
+ */
+static inline uint32_t
+rte_combine32ms1b(register uint32_t x)
+{
+       x |= x >> 1;
+       x |= x >> 2;
+       x |= x >> 4;
+       x |= x >> 8;
+       x |= x >> 16;
+
+       return x;
+}
+
+/**
+ * Combines 64b inputs most significant set bits into the least
+ * significant bits to construct a value with the same MSBs as x
+ * but all 1's under it.
+ *
+ * @param v
+ *    The integer whose MSBs need to be combined with its LSBs
+ * @return
+ *    The combined value.
+ */
+static inline uint64_t
+rte_combine64ms1b(register uint64_t v)
+{
+       v |= v >> 1;
+       v |= v >> 2;
+       v |= v >> 4;
+       v |= v >> 8;
+       v |= v >> 16;
+       v |= v >> 32;
+
+       return v;
+}
+
 /*********** Macros to work with powers of 2 ********/
 
 /**
@@ -266,15 +311,28 @@ static inline uint32_t
 rte_align32pow2(uint32_t x)
 {
        x--;
-       x |= x >> 1;
-       x |= x >> 2;
-       x |= x >> 4;
-       x |= x >> 8;
-       x |= x >> 16;
+       x = rte_combine32ms1b(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 = rte_combine32ms1b(x);
+
+       return x - (x >> 1);
+}
+
 /**
  * Aligns 64b input parameter to the next power of 2
  *
@@ -288,16 +346,28 @@ static inline uint64_t
 rte_align64pow2(uint64_t v)
 {
        v--;
-       v |= v >> 1;
-       v |= v >> 2;
-       v |= v >> 4;
-       v |= v >> 8;
-       v |= v >> 16;
-       v |= v >> 32;
+       v = rte_combine64ms1b(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 = rte_combine64ms1b(v);
+
+       return v - (v >> 1);
+}
+
 /*********** Macros for calculating min and max **********/
 
 /**