struct Edge
{
	unsigned short		vertexIndex[2];
	unsigned short		triangleIndex[2];
};

struct Triangle
{
	unsigned short		index[3];
};

long BuildEdges(long triangleCount,
		const Triangle *triangleArray, Edge **edgeArray)
{
	// Allocate enough space to hold all edges
	*edgeArray = new Edge[triangleCount * 3];

	long edgeCount = 0;
	Edge *edge = *edgeArray;

	// First pass: find edges
	const Triangle *triangle = triangleArray;
	for (long a = 0; a < triangleCount; a++)
	{
		long i1 = triangle->index[0];
		long i2 = triangle->index[1];
		long i3 = triangle->index[2];

		if (i1 < i2)
		{
			edge->vertexIndex[0] = i1;
			edge->vertexIndex[1] = i2;
			edge->triangleIndex[0] = a;
			edge->triangleIndex[1] = -1;
			edgeCount++;
			edge++;
		}

		if (i2 < i3)
		{
			edge->vertexIndex[0] = i2;
			edge->vertexIndex[1] = i3;
			edge->triangleIndex[0] = a;
			edge->triangleIndex[1] = -1;
			edgeCount++;
			edge++;
		}

		if (i3 < i1)
		{
			edge->vertexIndex[0] = i3;
			edge->vertexIndex[1] = i1;
			edge->triangleIndex[0] = a;
			edge->triangleIndex[1] = -1;
			edgeCount++;
			edge++;
		}

		triangle++;
	}

	// Second pass: match triangles to edges
	triangle = triangleArray;
	for (long a = 0; a < triangleCount; a++)
	{
		long i1 = triangle->index[0];
		long i2 = triangle->index[1];
		long i3 = triangle->index[2];
		
		if (i1 > i2)
		{
			edge = *edgeArray;
			for (long b = 0; b < edgeCount; b++)
			{
				if ((edge->vertexIndex[0] == i2) &&
					(edge->vertexIndex[1] == i1) &&
					(edge->triangleIndex[1] == -1))
				{
					edge->triangleIndex[1] = a;
					break;
				}

				edge++;
			}
		}
		
		if (i2 > i3)
		{
			edge = *edgeArray;
			for (long b = 0; b < edgeCount; b++)
			{
				if ((edge->vertexIndex[0] == i3) &&
					(edge->vertexIndex[1] == i2) &&
					(edge->triangleIndex[1] == -1))
				{
					edge->triangleIndex[1] = a;
					break;
				}

				edge++;
			}
		}
		
		if (i3 > i1)
		{
			edge = *edgeArray;
			for (long b = 0; b < edgeCount; b++)
			{
				if ((edge->vertexIndex[0] == i1) &&
					(edge->vertexIndex[1] == i3) &&
					(edge->triangleIndex[1] == -1))
				{
					edge->triangleIndex[1] = a;
					break;
				}

				edge++;
			}
		}
		
		triangle++;
	}
	
	return (edgeCount);
}