[dpdk-dev] [PATCH v4] eal: add API to align integer to previous power of 2
Pavan Nikhilesh
pbhagavatula at caviumnetworks.com
Wed Apr 4 15:20:16 CEST 2018
Add 32b and 64b API's to align the given integer to the previous power
of 2. Update common auto test to include test for previous power of 2 for
both 32 and 64bit integers.
Signed-off-by: Pavan Nikhilesh <pbhagavatula at caviumnetworks.com>
---
v4 Changes:
- Squash patchset into a single patch.
- Use %PRIu64 instead of %lu
lib/librte_eal/common/include/rte_common.h | 92 ++++++++++++++++++++++++++----
test/test/test_common.c | 26 +++++++++
2 files changed, 107 insertions(+), 11 deletions(-)
diff --git a/lib/librte_eal/common/include/rte_common.h b/lib/librte_eal/common/include/rte_common.h
index c7803e41c..7e147dcf2 100644
--- a/lib/librte_eal/common/include/rte_common.h
+++ b/lib/librte_eal/common/include/rte_common.h
@@ -223,6 +223,51 @@ 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 ********/
/**
@@ -250,15 +295,28 @@ 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
*
@@ -272,16 +330,28 @@ 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 **********/
/**
diff --git a/test/test/test_common.c b/test/test/test_common.c
index d0342430f..7361693b8 100644
--- a/test/test/test_common.c
+++ b/test/test/test_common.c
@@ -3,6 +3,7 @@
*/
#include <stdio.h>
+#include <inttypes.h>
#include <string.h>
#include <math.h>
#include <rte_common.h>
@@ -70,6 +71,9 @@ test_align(void)
#define FAIL_ALIGN(x, i, p)\
{printf(x "() test failed: %u %u\n", i, p);\
return -1;}
+#define FAIL_ALIGN64(x, j, q)\
+ {printf(x "() test failed: %"PRIu64" %"PRIu64"\n", j, q);\
+ return -1; }
#define ERROR_FLOOR(res, i, pow) \
(res % pow) || /* check if not aligned */ \
((res / pow) != (i / pow)) /* check if correct alignment */
@@ -80,6 +84,7 @@ test_align(void)
val / pow != (i / pow) + 1) /* if not aligned, hence +1 */
uint32_t i, p, val;
+ uint64_t j, q;
for (i = 1, p = 1; i <= MAX_NUM; i ++) {
if (rte_align32pow2(i) != p)
@@ -88,6 +93,27 @@ test_align(void)
p <<= 1;
}
+ for (i = 1, p = 1; i <= MAX_NUM; i++) {
+ if (rte_align32prevpow2(i) != p)
+ FAIL_ALIGN("rte_align32prevpow2", i, p);
+ if (rte_is_power_of_2(i + 1))
+ p = i + 1;
+ }
+
+ for (j = 1, q = 1; j <= MAX_NUM ; j++) {
+ if (rte_align64pow2(j) != q)
+ FAIL_ALIGN64("rte_align64pow2", j, q);
+ if (j == q)
+ q <<= 1;
+ }
+
+ for (j = 1, q = 1; j <= MAX_NUM ; j++) {
+ if (rte_align64prevpow2(j) != q)
+ FAIL_ALIGN64("rte_align64prevpow2", j, q);
+ if (rte_is_power_of_2(j + 1))
+ q = j + 1;
+ }
+
for (p = 2; p <= MAX_NUM; p <<= 1) {
if (!rte_is_power_of_2(p))
--
2.16.3
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