Optimizations

Building arrays via `arr[i] = x` is ~45% faster than `arr.push(x)`. See http://jsperf.com/sylvesterloops/2
Store references to mOrV.elements.
Inline loops instead of call out to map, which calls to forEach.
@megawac that actually seems detrimental in some browsers and only a minor improvement in others: http://jsperf.com/construct-array-of-fixed-size/2