comoving volume

hi,
I'm trying to calculate comoving volume in redshift between 0.004 and 3.2 , I have written a code in fortran but as I have to define steps very very small something like 0.00001 it takes days to run this code , I 'm sure there should be subroutines or some thing more logical, so I would appreciate if some one helps me here to solve my problem , also explain more precisely how this volume can be calculated