genericvector: Fix minimum size

Commit 907de5995f tried to improve
GenericVector, but missed a case where vectors with less than
kDefaultVectorSize were allocated. This resulted in additional
alloc / free operations.

Commit a28b2a033d (before memory optimization)
oem 0: total heap usage: 739,238 allocs, 739,237 frees, 161,699,214 bytes allocated
oem 1: total heap usage: 690,182 allocs, 690,175 frees, 144,470,400 bytes allocated
oem 2: total heap usage: 728,213 allocs, 728,206 frees, 182,885,824 bytes allocated

Commit fd3f8f9b2d without genericvector change
oem 0: total heap usage: 738,980 allocs, 738,979 frees, 161,697,150 bytes allocated
oem 1: total heap usage: 690,182 allocs, 690,175 frees, 144,470,400 bytes allocated
oem 2: total heap usage: 728,213 allocs, 728,206 frees, 182,885,824 bytes allocated
=> Improvements for oem 0, no change for oem 1 and oem 2.

Commit fd3f8f9b2d
oem 0: total heap usage: 772,648 allocs, 772,647 frees, 160,083,901 bytes allocated
oem 1: total heap usage: 748,591 allocs, 748,584 frees, 143,581,672 bytes allocated
oem 2: total heap usage: 764,796 allocs, 764,789 frees, 181,212,197 bytes allocated
=> Less bytes allocated, but more allocs / frees = bad for performance.

Commit fd3f8f9b2d with this patch
oem 0: total heap usage: 677,537 allocs, 677,536 frees, 160,444,634 bytes allocated
oem 1: total heap usage: 653,812 allocs, 653,805 frees, 143,423,008 bytes allocated
oem 2: total heap usage: 670,029 allocs, 670,022 frees, 181,517,760 bytes allocated
=> Improvements for all three cases.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

ccutil/genericvector.h

@@ -658,6 +658,7 @@ template <typename T>
 void GenericVector<T>::reserve(int size) {
   if (size_reserved_ >= size || size <= 0)
     return;
+  if (size < kDefaultVectorSize) size = kDefaultVectorSize;
   T* new_array = new T[size];
   for (int i = 0; i < size_used_; ++i)
     new_array[i] = data_[i];