calloc

[Dieter Rothmeier]

According to Harbison + Steele's book, calloc returns a region of
memory with all bits set to zero. They also point out that pointers
filled with zero bits do not necessarily have the value NULL, nor
do arithmetic values consisting of zero bits have necessarily have the value 
zero. How can this be? I always thought a pointer consisting of zero bits
is NULL. 

A puzzled programmer,
Dieter Rothmeier