      subroutine passb (nac,ido,ip,l1,idl1,cc,c1,c2,ch,ch2,wa)
      implicit double precision (a-h,o-z)
      dimension       ch(ido,l1,ip)          ,cc(ido,ip,l1)          ,
     1                c1(ido,l1,ip)          ,wa(1)      ,c2(idl1,ip),
     2                ch2(idl1,ip)
      idot = ido/2
      nt = ip*idl1
      ipp2 = ip+2
      ipph = (ip+1)/2
      idp = ip*ido
c
      if (ido .lt. l1) go to 106
      do 103 j=2,ipph
         jc = ipp2-j
         do 102 k=1,l1
            do 101 i=1,ido
               ch(i,k,j) = cc(i,j,k)+cc(i,jc,k)
               ch(i,k,jc) = cc(i,j,k)-cc(i,jc,k)
  101       continue
  102    continue
  103 continue
      do 105 k=1,l1
         do 104 i=1,ido
            ch(i,k,1) = cc(i,1,k)
  104    continue
  105 continue
      go to 112
  106 do 109 j=2,ipph
         jc = ipp2-j
         do 108 i=1,ido
            do 107 k=1,l1
               ch(i,k,j) = cc(i,j,k)+cc(i,jc,k)
               ch(i,k,jc) = cc(i,j,k)-cc(i,jc,k)
  107       continue
  108    continue
  109 continue
      do 111 i=1,ido
         do 110 k=1,l1
            ch(i,k,1) = cc(i,1,k)
  110    continue
  111 continue
  112 idl = 2-ido
      inc = 0
      do 116 l=2,ipph
         lc = ipp2-l
         idl = idl+ido
         do 113 ik=1,idl1
            c2(ik,l) = ch2(ik,1)+wa(idl-1)*ch2(ik,2)
            c2(ik,lc) = wa(idl)*ch2(ik,ip)
  113    continue
         idlj = idl
         inc = inc+ido
         do 115 j=3,ipph
            jc = ipp2-j
            idlj = idlj+inc
            if (idlj .gt. idp) idlj = idlj-idp
            war = wa(idlj-1)
            wai = wa(idlj)
            do 114 ik=1,idl1
               c2(ik,l) = c2(ik,l)+war*ch2(ik,j)
               c2(ik,lc) = c2(ik,lc)+wai*ch2(ik,jc)
  114       continue
  115    continue
  116 continue
      do 118 j=2,ipph
         do 117 ik=1,idl1
            ch2(ik,1) = ch2(ik,1)+ch2(ik,j)
  117    continue
  118 continue
      do 120 j=2,ipph
         jc = ipp2-j
         do 119 ik=2,idl1,2
            ch2(ik-1,j) = c2(ik-1,j)-c2(ik,jc)
            ch2(ik-1,jc) = c2(ik-1,j)+c2(ik,jc)
            ch2(ik,j) = c2(ik,j)+c2(ik-1,jc)
            ch2(ik,jc) = c2(ik,j)-c2(ik-1,jc)
  119    continue
  120 continue
      nac = 1
      if (ido .eq. 2) return
      nac = 0
      do 121 ik=1,idl1
         c2(ik,1) = ch2(ik,1)
  121 continue
      do 123 j=2,ip
         do 122 k=1,l1
            c1(1,k,j) = ch(1,k,j)
            c1(2,k,j) = ch(2,k,j)
  122    continue
  123 continue
      if (idot .gt. l1) go to 127
      idij = 0
      do 126 j=2,ip
         idij = idij+2
         do 125 i=4,ido,2
            idij = idij+2
            do 124 k=1,l1
               c1(i-1,k,j) = wa(idij-1)*ch(i-1,k,j)-wa(idij)*ch(i,k,j)
               c1(i,k,j) = wa(idij-1)*ch(i,k,j)+wa(idij)*ch(i-1,k,j)
  124       continue
  125    continue
  126 continue
      return
  127 idj = 2-ido
      do 130 j=2,ip
         idj = idj+ido
         do 129 k=1,l1
            idij = idj
            do 128 i=4,ido,2
               idij = idij+2
               c1(i-1,k,j) = wa(idij-1)*ch(i-1,k,j)-wa(idij)*ch(i,k,j)
               c1(i,k,j) = wa(idij-1)*ch(i,k,j)+wa(idij)*ch(i-1,k,j)
  128       continue
  129    continue
  130 continue
      return
      end
