Array Traversal i++ vs i--

Array Bounds-Check Removal

One of the optimization done in .NET CLR is removing bounds-check when accessing arrays. It's done in certain cases and this excellent blog post discusses these cases (http://blogs.msdn.com/b/clrcodegeneration/archive/2009/08/13/array-bounds-check-elimination-in-the-clr.aspx)

Something that I found really interesting is that it matters as far as bounds-check elimination is concerned whether arrays traversed in an increasing or decreasing order.

for(var i=0;i<someArray.Length;i++){ //array access using i} vs. for(var i=someArray.Length-1;i>=0;i--) { //array access using i }

 So in accessing the array within with the first loop, the bound check is eliminated but in the in the second case (decreasing; i--). The mentioned posts recommend traversing the array in ascending order whenever possible.

Another useful advice from the post is that using the Length property in the condition statement of a for loop is better than using a local variable (unless the local variable is intended to access a subset of the array of course). Interesting stuff.