#-- the sub that computes the data (@result) only from it's parameters (@pars)
#   Using @result as an array is just for simplicity. It could be hash-ref or an object
#   or whatever your expected result fits into...
#
sub get_result { my (@pars) = @_; ..... return @result; }


#-- here's your CGI handler
#
sub cgi_handler {
                   ...
                   my (@pars) = ... #-- get params from HTTP request
                   my (@result) = get_result( @pars ); 
                   ...              #-- render HTTP-response from your @result
}


#-- somewhere else in your code... where your original question came from...
#   Instead of a regular function, an object method or a class method or an AUTOSUB etc. 
#   could be called.
#
sub somewhere_else {
  #-- no worry to call cgi_handler(), just call
  @result = get_result( @pars );
  ...
}