9 / VERSION 5A 4-27-77 PT
25 ATPI, F 1.570796 /PI/2
41 FLDA% BPATN2,1 /ADDR OF Y
43 FLDA% BPATN2,1+ /ADDR OF X
46 FLDA% YCOR /GET Y - THE TAN
47 FSTA YCOR /SAV FOR A SECOND
52 ATN1, FLDA% XCOR /GET X - THE QUADRAND
53 FSTA XCOR /+MOVE IT TO A SAFE PLACE
60 JA .+4 /TAKE ARCTAN OF Y/X
62 FSTA YCOR /SAVE IT AWAY
63 JGE A2 /SKIP IF 1 OR 3 Q
64 FADD FPIAT2 /ADD PI FOR 4TH Q
68 FSUB FPIAT2 /SUB PI FOR 2ND+3RD QUADS
70 ATASP, FLDA ATPI /X=0 MEANS +-PI/2
75 JLT POSX /IF X POS,ANS IS 0
78 POSX, FLDA FPIAT2 /OTHERWISE,ANS IS PI