\ fatan 05.8.10 NAB

module fatan

: f+u ( u -- ) ( F: r -- r+u )  0 d>f f+ ;
: f*u ( u -- ) ( F: r -- r*u )  0 d>f f* ;

57.2957795130823e fconstant radsize

public:
\ Source: Abramowitz and Stegun.

: FATAN ( r -- arctan )
  fdup  ( F: r r )
  fdup fdup f* fswap  ( F: r r^2 r )
  13e f* fround f>d drop abs 9 + 
  0e  ( F: r r^2 0 )
  for  ( F: r r^2 val ) ( -- )
    \ val=(i*i*r^2)/(i+i+1+val):
    i 2* 3 +  f+u  ( F: r r^2 tb )
    fover  i 1+ 0 d>f fdup f*  f*  ( F: r r^2 tb ta )
    fswap f/  ( F: r r^2 ta/tb )
  next  ( F: r r^2 val )
  fswap fdrop  ( F: r val )
  \ val=r/(1+val):
  1e f+ f/  ( F: arctan ) ;

: deg>rad ( deg -- rad )  radsize f/ ;
: rad>deg ( rad -- deg )  radsize f* ;

end-module