1 /ARCTANGENT ROUTINE OS8 FORTRAN II LIBRARY
11 /COPYRIGHT (C) 1974,1977 BY DIGITAL EQUIPMENT CORPORATION
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46 / VERSION NUMBER IS AVAILABLE AT ENTRY POINTS
65 DCA ACH /TAKE ABSVAL OF ARGUMENT
67 DCA SIGN /AND REMEMBER SIGN
72 JMS INVRS /INVERT ARG - SUBTRACT RESULT FROM PI/2
74 LSTN45, DCA L4# /L4# IS THE "PI/2-RESULT" SWITCH
76 TAD (-1774 /THIS IS AN APPROXIMATE TEST TO SEE
77 SPA CLA /IF THE NEW ARG IS <2-SQRT(3)
79 CALL 1,FAD /PERFORM A "DIFFERENCE OF TANGENTS"
80 ARG SQRT3 /TRANSFORMATION TO SUBTRACT PI/6
82 JMS INVRS /FROM THE RESULT. THE ARG IS TRANSFORMED
83 CALL 0,CHS /INTO SQRT(3)-4/(ARG+SQRT(3))
87 LSTN15, DCA INVRS /USE INVRS AS A SWITCH TO INDICATE THIS
88 CALL 1,STO /TRANSFORMATION OCCURRED
94 ATLOOP, INC L3# /NOW PERFORM A STANDARD TAYLOR SERIES
95 INC L3# /EXPANSION (WITH TRUNCATED COEFFICIENTS)
97 CALL 1,FAD /CONVERGENCE WILL BE GOOD SINCE WE
98 L3, ARG SQRT3 /HAVE MADE THE ARGUMENT BE <.3
105 ARG T /FINISH UP THE SERIES
108 CALL 1,FAD /ADD PI/6 IF NECESSARY
112 CALL 0,CHS /SUBTRACT FROM PI/2 IF NECESSARY
116 TAD ACH /SET SIGN OF RESULT = SIGN OF ARGUMENT
120 INVRS, 0 /INVERSION SUBROUTINE
121 TAD (2014 /ENTERED WITH AC=0 OR 20
122 DCA L4 /AC=0 MEANS 1/FAC, AC=20 MEANS 4/FAC
126 DCA ACH /ACM AND ACL WERE CLEARED BY STORE
131 FMPT, 0 /SUBROUTINE TO MULTIPLY BY T
132 CALL 1,FMP /SAVES A FEW MEASLY LOCATIONS
136 SIGN, 0 /CELL FOR HOLDING SIGN OF ARG
137 T, BLOCK 3 /FLOATING TEMPORARY
141 PIOVR6, 2004;1405;2216 /PI/6
142 PIOVR2, 2016;2207;7325
143 SQRT3, 2016;7331;7272 /SQRT(3)
144 /THE NEXT 4 NUMBERS MUST IMMEDIATELY FOLLOW SQRT3
145 1756;0462;4562 /APPROXIMATELY 1/9
146 5764;4221;3403 /APPROXIMATELY -1/7
147 1766;3141;6672 /APPROXIMATELY 1/5
148 5775;2525;2337 /APPROXIMATELY -1/3