MergeSort with minimum allocations

The most recent assignment in my data structures class was writing a sort comparison, including a MergeSort. I realize that MergeSort can't be in-place, but I wondered if there was a way to keep the memory allocations to a minimum. I came up with this, which uses one extra buffer (the same size as the source array). After each pass, the source buffer becomes the target and vice versa. Timings indicate that (for arrays containing random numbers), this beats a quicksort. (Apologies for reformatting introduced by HTML...)

int *IterativeMergeSorter::Sort() {
int* src = mArray;
int* tgt = new int[mLength];
for (int swapSize = 1; swapSize < mLength; swapSize *= 2) {
for (int j = 0; j < mLength; j += (2 * swapSize)) {
int start = j;
int sizeOfSrc1 = min(swapSize, mLength - start);
int src2Index = start + swapSize;
int remainder = max(0, mLength - src2Index);
int sizeofSrc2 = min(swapSize, remainder);
Merge(&tgt[start], &src[start], sizeOfSrc1,
&src[src2Index], sizeofSrc2);
}
int* temp = src;
src = tgt;
tgt = temp;
}
if (src != mArray) {
memcpy(mArray, src, mLength * sizeof(int));
tgt = src;
}
delete[] tgt;
return mArray;
}