how to write a program on matlab

I have a program written on Matlab as follows:

if nargin <2
    error('PERMS1:minrhs','Two Input Arguments are required.')
end
if fix(n) ~= n || fix(b) ~= b ||n < 0 || b < 0 || ~isa(n,'double') || ~isa(b,'double') || ~isreal(n) || ~isreal(b)
  error('PERMS1:nnegint','Input Parameters n and b Must be Non-negative Integers');
end
a=factorial(n:-1:1);
if b>a
    error('PERMS1:brange','Input Parameter b Should be between 1 and n!')
end

p=zeros(1,n);                       %initialize output variable
idx=ones(1,n);                      %initialize loop counters
id=find(a<b,1);                     %locate the level at which the given index stands
for i=id-1:n-1                      %work down to figure out the counter states (idx) in each inner loop
    d=mod(b,a(i+1));                %how far down this loop?
    idx(i)=floor(b/a(i+1))+(d~=0);  %set counter, account for counter resetting
    b=d;
    if d==0                        %adjust indices of inner loops if current loop is reset
        for j=i+1:n-1
            idx(j)=n-j+1;
        end
        break;
    end
end
m=1:n;                  %all possible indices
for i=1:n
    p(i)=m(idx(i));     %set permutation index according to current counter index
    m=m(m~=p(i));       %current premutation index is no longer available
end

n = 8;
x0 = 13294;
c = 21;
x = zeros(1,256);
xi = x0;
i3=zeros(1,n);
for k = 1:256
    i2 = floor(sin((pi/2)*((xi/(gt - 1))+((c+1)/(gt + 1))))*(gt - 1));
    I2 = perms1(8,i2+1);
    I1 = perms1(8,xi+1);
    for i=1:n
        i3(i)= I1(I2(i));
    end
    for i = 1:gt 
            if i3==perms1(8,i)
                x(k)=i;
                break;
            end
    end
    xi = x(k);
    disp(['k=',int2str(k),'x(k)=', int2str(x(k))]);
end
S = zeros(1,256);
for j = 1:256
    S(j)= j ;
end
for i = 1 :256
    j = floor(x(i)/gt*2^8);
    if j==0
        j=256;
    end
    t = 2^8 - i;
    if t==0
        t=256
    end
    a = S(j);
    S(j)= S(t);
    S(t) = a;
end
for i = 1:256
    disp(S(i));
end
xlswrite('D:\test.xlsx',S);

I want to convert i, j = 1: 256 to 0: 255, what should I do?

Please help me!

Answer 1

[Walter Roberson]

for j = 0:255
    S(j+1)= j+1;
end
for i = 0 :255
    j = floor(x(i+1)/gt*2^8);
    if j==-1      %cannot happen
        j=255;
    end
    t = 2^8 - (i+1);
    if t==-1     %cannot happen
        t=255
    end
    a = S(j+1);
    S(j+1)= S(t+1);
    S(t+1) = a;
end
for i = 0:255
    disp(S(i+1));
end