factorial using level 2 s-function

hi, i am writing a code to find a factorial using level 2 s-function. the main thing is to learn about the discrete states. i am beginner in a s function. when i run the code in the simulink with constant block and display block as input and output. iam getting '0' as output.

can anyone tell me what i am doing wrong within this code. and suggest me some reference material to learn about s-function to the beginner. all i find till now is whole bunch of codes. which i barely understand.

the code is,

function anil2sfun(block)
function setup(block)
block.numinputports = 1;
block.numoutputports = 1;
block.setprecompinpportinfotodynamic;
block.setprecompoutportinfotodynamic;
block.inputport(1).directfeedthrough = true;
block.regblockmethod('postpropagationsetup', @dopostpropsetup);
block.regblockmethod('outputs', @output);
block.regblockmethod('update', @update);
block.regblockmethod('initializeconditions', @initialconditions);
function dopostpropsetup(block)
block.numdworks = 1;
block.dwork(1).name = 'x0' ;
block.dwork(1).dimensions = 1;
block.dwork(1).datatyprID = 0;
block.dwork(1).complexity = 'real';
block.dwork(1).usedasdiscstate = true;
function output(block)
block.outputport(1).data= block.dwork(1).data * block.inputport(1).data ;
function update(block)
if block.dwork(1).data < block.inputport(1).data 
    block.dwork(1).data =block.dwork(1).data + 1;
end

function initialconditions(block)
block.dwork(1).data=1;
%block.dwork(1).data=block.dialogprm(1).data;