Basically, the corridor takes up the whole width of the map, from -4096 to +4096 units. The game stores player coordinates in the form of eights of one unit, i.e. a change in position of 1 = 0.125 units. The positions are stored in a 2-byte integer, which has 65536 possible values. This is where the maximum map size comes from: 65536/8 = 8192 possibilities, which are mapped from -4096 to +4096. When you get "past" the edge of the map, the number containing your coordinate wraps-around, i.e. if you're at (4095, 0, 0) and you move 1 unit forward in the x direction, you will find yourself at (0, 0, 0). Because you never actually touched the wall, your velocity remains the same.
As to what Chef-Killer says, I think it is possible if you used a tweaked compiler, I will do some tests.