depth and picking

I’m having trouble verifying the z values returned by picking. The red book says, and internet searches agree, that the value varies from 0.0 to 1.0 with the returned value first being multiplied by 2^32-1 ( which is ffffffff ) and then rounded to the nearest unsigned integer ( p. 474 of the red book, version 1.1 ). Code on p. 477 prints out the values after being divided by 7fffffff.

  1. Is the count measured from the eye(0) to infinity(1.0)? Or between the near plane of a frustum (0.0) and the far (1.0)?
  2. Why is the divisor 7fffffff? It would seem to need ffffffff to divide back to the original number? The printed values are about 1.5 for my model.