\ Simulation of Drunkard's Walk in 2 space dimensions
\
\ ---------------------------------------------------
\     (c) Copyright 2000  Julian V. Noble.          \
\       Permission is granted by the author to      \
\       use this software for any application pro-  \
\       vided this copyright notice is preserved.   \
\ ---------------------------------------------------

\ This is an ANS Forth program requiring the
\   FLOAT, FLOAT EXT, FILE and TOOLS EXT wordsets.
\
\ Environmental dependences:
\       Assumes independent floating point stack

MARKER -walk

needs prng.f

\ needs arrays.f

\ Words for splitting a 32-bit integer into 16-bit parts:
\   n = x*2^16 + y

\ HEX  10000 CONSTANT 2^16  DECIMAL

\ : split     ( n -- x y)    2^16  /MOD  ;


\ 1000 CONSTANT Nmax
\ Nmax long 1 CELLS 1array pos{       \ integer-valued vector of
                                    \ visited points


0.1 seed 2!     \ initialize prng

0 VALUE x_now
0 Value y_now

: new_point     \ move to a new location
    prng    4e0  f*  F>S
    CASE
        0  OF  x_now 1+  TO  x_now  ENDOF
        1  OF  x_now 1-  TO  x_now  ENDOF
        2  OF  y_now 1+  TO  y_now  ENDOF
        3  OF  y_now 1-  TO  y_now  ENDOF
    ENDCASE
;


: walk      \ perform the random walk
    0 TO x_now      0 TO y_now      \ initialize
    0 DO  new_point  cr  x_now .  y_now .   LOOP
;