Add method the considers elemsize when computing number of elements that will maximize 2^N bytes block

2 files changed, 21 insertions, 0 deletions

diff --git a/vespalib/src/tests/alloc/alloc_test.cpp b/vespalib/src/tests/alloc/alloc_test.cpp
index c52170fc8ec..d37abb15c2f 100644
--- a/vespalib/src/tests/alloc/alloc_test.cpp
+++ b/vespalib/src/tests/alloc/alloc_test.cpp
@@ -47,6 +47,21 @@ TEST("test roundUp2inN") {
     EXPECT_EQUAL(16u, roundUp2inN(9));
 }
 
+TEST("test roundUp2inN elems") {
+    EXPECT_EQUAL(0u, roundUp2inN(0, 17));
+    EXPECT_EQUAL(1u, roundUp2inN(1, 17));
+    EXPECT_EQUAL(3u, roundUp2inN(2, 17));
+    EXPECT_EQUAL(3u, roundUp2inN(3, 17));
+    EXPECT_EQUAL(7u, roundUp2inN(4, 17));
+    EXPECT_EQUAL(7u, roundUp2inN(5, 17));
+    EXPECT_EQUAL(7u, roundUp2inN(6, 17));
+    EXPECT_EQUAL(7u, roundUp2inN(7, 17));
+    EXPECT_EQUAL(15u, roundUp2inN(8, 17));
+    EXPECT_EQUAL(15u, roundUp2inN(9, 17));
+    EXPECT_EQUAL(15u, roundUp2inN(15, 17));
+    EXPECT_EQUAL(30u, roundUp2inN(16, 17));
+}
+
 TEST("test basics") {
     {
         Alloc h = Alloc::allocHeap(100);
diff --git a/vespalib/src/vespa/vespalib/util/alloc.h b/vespalib/src/vespa/vespalib/util/alloc.h
index 71a3bd2407a..a1bb6af6514 100644
--- a/vespalib/src/vespa/vespalib/util/alloc.h
+++ b/vespalib/src/vespa/vespalib/util/alloc.h
@@ -80,8 +80,14 @@ private:
 
 namespace vespalib {
 
+/// Rounds up to the closest number that is a power of 2
 inline size_t roundUp2inN(size_t minimum) {
     return 2ul << Optimized::msbIdx(minimum - 1);
 }
 
+/// Rounds minElems up to the closest number where minElems*elemSize is a power of 2
+inline size_t roundUp2inN(size_t minElems, size_t elemSize) {
+    return roundUp2inN(minElems * elemSize)/elemSize;
+}
+
 }