\def\date{06 Jan 2012}\def\source{V1, p.\ 178}\def\author{Udo Wermuth}\input mmix =-3
!!\clearline{\tenbf Program J} ({\tenit Inverse in place\/})\smallskip
N         IS        6                   !! Number of elements in the permutation
t         IS        $255                !! Temporary storage
i         IS        $2                  !! Variables of the algorithm
ii        IS        i                   !! Two characters indicate that the
jj        IS        $3                  !! \quad variable is multiplied by 8
k         IS        jj
mm        IS        $4
          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--4
          LOC       #100
* Inverse a permutation in place        !! \startnumbering
Invert    SET       t,N                 !1! \step J1. Negate all. $t\gets n$.
          SL        mm,t,3              !1! $m\gets n$.
1H        LDO       k,X,mm              !N!
          NEG       k,k                 !N!
          STO       k,X,mm              !N! $X[k]\gets -X[k]$.
          SUB       mm,mm,8             !N! $m\gets m-1$.
          PBP       mm,1B               !N!\bad 1\bad Branch if $m>0$.
          SL        mm,t,3              !1! $m\gets n$.
2H        SR        i,mm,3              !N! \step J2. Initialize. $i\gets m$.
3H        SL        jj,i,3              !A! \step J3. Find neagtive entry. $j\gets i$.
          LDO       i,X,jj              !A! $i\gets X[j]$.
          PBP       i,3B                !A!\bad N\bad To J3 if $i>0$.
4H        NEG       i,i                 !N! \step J4. Invert.
          SL        ii,i,3              !N!
          LDO       t,X,ii              !N! $t\gets X[-i]$
          STO       t,X,jj              !N! \quad and $X[j]\gets X[-i]$.
          SR        t,mm,3              !N! $t\gets m$
          STO       t,X,ii              !N! \quad and $X[-i]\gets m$.
5H        SUB       mm,mm,8             !N! \step J5. Loop on $m$. $m\gets m-1$.
          PBP       mm,2B               !N!\bad 1\bad Branch if $m>0$.\stopnumbering
* inspect memory locations of array X for the result
          TRAP      0,Halt,0
Main      IS        Invert              !! \eop
!!\endwAoA\bye