\def\date{04 Jan 2012}\def\source{V1, p.\ 177}\def\author{Udo Wermuth}\input mmix =-3
!!\clearline{\tenbf Program I} ({\tenit Inverse in place\/})\smallskip
N         IS        6                   !! Number of elements in the permutation
j         IS        $2                  !! Variables of the algorithm
i         IS        $3
mm        IS        $4                  !! For $m$ the value is multiplied by 8
          LOC       Data_Segment
X         GREG      @
          OCTA      0                   !! $X[0]$ is not used
          OCTA      6,2,1,5,4,3         !! The data of Table 1.3.3--3
          LOC       #100
* Inverse a permutation in place        !! \startnumbering
Invert    SET       mm,N                !1! \step I1. Initialize.
          SL        mm,mm,3             !1! $m\gets n$.
          NEG       j,1                 !1! $j\gets-1$.
2H        LDO       i,X,mm              !N! \step I2. Next element. $i\gets X[m]$.
          PBN       i,5F                !N!\bad C\bad To I5 if $i<0$.
3H        STO       j,X,mm              !N! \step I3. Invert one. $X[m]\gets j$.
          SR        j,mm,3              !N! 
          NEG       j,j                 !N! $j\gets-m$.
          SL        mm,i,3              !N! $m\gets i$.
          LDO       i,X,mm              !N! $i\gets X[m]$.
4H        PBP       i,3B                !N!\bad C\bad \steq I4. End of cycle? To I3 if $i>0$.
          SET       i,j                 !C! Otherwise set $i\gets j$.
5H        NEG       i,i                 !N! \step I5. Store final value.
          STO       i,X,mm              !N! $X[m]\gets-i$.
6H        SUB       mm,mm,8             !N! \step I6. Loop on $m$.
          PBP       mm,2B               !N!\bad 1\bad To I2 if $m>0$. \stopnumbering
* inspect memory locations of array X for the result
          TRAP      0,Halt,0
Main      IS        Invert              !! \eop
!!\endwAoA\bye