\ ftrig2 05.08.09 NAB
needs fatan
needs ftrig

: ftan ( F: f1 -- f2 )
  fdup fsin fswap fcos f/ ;

: fatan2 ( F: y x -- f )
  fdup f0=  ( x=0? )
  if  fdrop fdup f0= 0=  ( y=0? )
    if  f0< pi
      if  fnegate  then
      2e f/
    then
    exit
  then
  fover f0<  ( y<0)
  fdup f0<  ( x<0)
  f/ fatan
  if ( x<0)  pi
    if ( y<0)  f-  else  f+  then
  else  drop  then ;

: facos ( F: r1 -- r2 )
  1e fover fdup f*  ( Cr1 1 Cr1^2 )
  f- fsqrt  ( Cr1 1-Cr1^2^.5 )
  fswap  fatan2 ;

: fasin ( F: r1 -- r2 )
  1e fover fdup f* ( Sr1 1 Sr1^2 )
  f- fsqrt ( Sr1 1-Sr1^2^.5 )
  fatan2 ;