7 /SUBROUTINE DATAN2(Y,X)
9 / VERSION 5A 4-27-77 PT
52 FLDA% BPATN2,1 /ADDR OF Y
54 FLDA% BPATN2,1+ /ADDR OF X
58 FSTA YCOR /SAVE FOR A SECOND
63 ATN1, FLDA% XCOR /GET X - THE QUADRAND
64 FSTA XCOR /+MOVE IT TO A SAFE PLACE
71 JA .+4 /TAKE ARCTAN OF Y/X
73 FSTA YCOR /SAVE IT AWAY
74 JGE A2 /SKIP IF 1ST OR 3RD QUADS
75 FADD FPIAT2 /ADD PI FOR 4TH QUAD
77 A2, JXN AT2RTN,2 /DONE IF 1 OR 4 Q
79 FSUB FPIAT2 /2ND OR 3RD Q
81 ATASP, FLDA ATPI /PI/2
89 POSX, FLDA FPIAT2 /X LT 0, ANS = PI