Mapping range of addresses

[shreyas krishnan]

Hi , 
      I am looking for an efficient data structure  to map from a
range of addresses to a single address.  As it is used at runtime,  I
want it to be as efficient as possible, with perhaps updaing more
important that retreiving.  Are there any examples of  such data
structure  ( and optimized code to use it)  in gcc,binutils  ?

thanks 
Shrey