From: Mike D. Lowis <mike@mdlowis.com>
Date: Thu, 11 Apr 2013 19:47:14 +0000 (-0400)
Subject: Updated vector to allocate in powers of 2
X-Git-Url: https://git.mdlowis.com/?a=commitdiff_plain;h=d98a68159061bab3666dee6b6099c4fd5ce3741b;p=projs%2Flibcds.git

Updated vector to allocate in powers of 2
---

diff --git a/source/vector/vec.c b/source/vector/vec.c
index 19f9f23..298f685 100644
--- a/source/vector/vec.c
+++ b/source/vector/vec.c
@@ -1,8 +1,8 @@
 /**
-    @file vec.c
-    @brief See header for details
-    $Revision$
-    $HeadURL$
+  @file vec.c
+  @brief See header for details
+  $Revision$
+  $HeadURL$
 */
 #include "vec.h"
 #include <stdlib.h>
@@ -70,7 +70,7 @@ void vec_resize(vec_t* p_vec, size_t size, void* data)
 {
     if (size > p_vec->size)
     {
-        vec_reserve(p_vec,size);
+        vec_reserve(p_vec,vec_next_capacity(size));
         for (p_vec->size; p_vec->size < size; p_vec->size++)
         {
             p_vec->p_buffer[ p_vec->size ] = data;
@@ -84,6 +84,23 @@ void vec_resize(vec_t* p_vec, size_t size, void* data)
     }
 }
 
+size_t vec_next_capacity(size_t req_size)
+{
+    size_t next_power = req_size;
+    size_t num_bits = sizeof(size_t) * 8;
+    size_t bit_n;
+
+    /* Find the next highest power of 2 */
+    next_power--;
+    for (bit_n = 1; bit_n < num_bits; bit_n = bit_n << 1)
+    {
+        next_power = next_power | (next_power >> bit_n);
+    }
+    next_power++;
+
+    return next_power;
+}
+
 void vec_shrink_to_fit(vec_t* p_vec)
 {
     p_vec->p_buffer = realloc( p_vec->p_buffer, sizeof(void*) * p_vec->size );
@@ -133,8 +150,8 @@ bool vec_insert(vec_t* p_vec, size_t index, size_t num_elements, ...)
         vec_resize( p_vec, p_vec->size + num_elements, NULL );
         /* Move the displaced items to the end */
         memcpy( &(p_vec->p_buffer[index + num_elements]),
-                &(p_vec->p_buffer[index]),
-                sizeof(void*) * (p_vec->size - index));
+            &(p_vec->p_buffer[index]),
+            sizeof(void*) * (p_vec->size - index));
         /* insert the new items */
         va_start(elements, num_elements);
         new_size = index + num_elements;
@@ -162,8 +179,8 @@ bool vec_erase(vec_t* p_vec, size_t start_idx, size_t end_idx)
         }
         /* Compact the remaining data */
         memcpy( &(p_vec->p_buffer[start_idx]), /* Destination is beginning of erased range */
-                &(p_vec->p_buffer[end_idx+1]), /* Source is end of erased range */
-                sizeof(void*) * (p_vec->size - end_idx));
+            &(p_vec->p_buffer[end_idx+1]), /* Source is end of erased range */
+            sizeof(void*) * (p_vec->size - end_idx));
         /* Shrink the size */
         p_vec->size = p_vec->size - ((end_idx - start_idx) + 1);
         ret = true;
diff --git a/source/vector/vec.h b/source/vector/vec.h
index 99125ae..aa9d2d7 100644
--- a/source/vector/vec.h
+++ b/source/vector/vec.h
@@ -91,6 +91,15 @@ bool vec_empty(vec_t* p_vec);
  */
 void vec_resize(vec_t* p_vec, size_t size, void* data);
 
+/**
+ * @brief Returns the next power of two that is not less than the desired size.
+ *
+ * @param req_size The desired size of the vector.
+ *
+ * @return The necessary capacity.
+ */
+size_t vec_next_capacity(size_t req_size);
+
 /**
  * @brief Shrinks the vector's capacity to equal it's size.
  *
diff --git a/tests/test_vec.cpp b/tests/test_vec.cpp
index 4897aaa..8711815 100644
--- a/tests/test_vec.cpp
+++ b/tests/test_vec.cpp
@@ -145,7 +145,7 @@ namespace {
 
         CHECK( false == p_vec->own_contents );
         CHECK( 5 == p_vec->size );
-        CHECK( 5 == p_vec->capacity );
+        CHECK( 8 == p_vec->capacity );
         CHECK( (void*)0x2A == p_vec->p_buffer[3] );
         CHECK( (void*)0x2A == p_vec->p_buffer[4] );
 
@@ -378,4 +378,26 @@ namespace {
         vec_clear( &vector );
         CHECK(0 == vector.size);
     }
+
+    //TEST(foo)
+    //{
+    //    size_t next_power = 9;
+    //    size_t num_bits = sizeof(size_t) * 8;
+    //    size_t bit_n;
+
+    //    next_power--;
+    //    for (bit_n = 1; bit_n < num_bits; bit_n = bit_n << 1)
+    //    {
+    //        next_power = next_power | (next_power >> bit_n);
+    //    }
+    //    next_power++;
+
+    //    std::cout << next_power << std::endl;
+
+    //    //int n = 7;
+    //    //int exp = 0;
+    //    //while(n>1) { n = n>>1; exp++; }
+    //    //while(exp>=0) { n = n<<1; exp--; }
+    //    //std::cout << n << " " << exp << std::endl;
+    //}
 }