  To accelerate the algorithms for the dihedral hidden subgroup problem, we
present a new algorithm based on algorithm SV(shortest vector). A subroutine is
given to get a transition quantum state by constructing a phase filter
function, then the measurement basis are derived based on the technique for
solving low density subset problem. Finally, the parity of slope is revealed by
the measurements on the transition quantum state. This algorithm takes O(n)
quantum space and O(n^2) classical space, which is superior to existing
algorithms, for a relatively small n(n<6400),it takes (n^0.5)*(log(max aij))^3
computation time, which is superior to 2^(O(n^0.5)).
