BASIC-MTHPAK

* NAME BASIC-MTHPAK DOC. 70181832000 REV. A PAGE 49

1707 * 1708 * 1709 * ARCTANGENT FUNCTION ROUTINE 1710 * 1711 * CALLING SEQUENCE: 1712 * 1713 * JST ATNF 1714 * DAC ARG POINTER TO THE ARGUMENT 1715 * ......RETURN ARCTANGENT OF ARGUMENT IN A AND B REGISTERS 1716 * 1717 * 1718 * A SIGN FLAG AND A SCALE FACTOR FLAG ARE INITIALZED TO MINUS 1719 * TWO. THE ARGUMENT IS LOADED, AND IF IT IS POSITIVE, THE SIGN FLAG 1720 * IS INCREMENTED BY ONE. IF THE ARGUMENT IS NEGATIVE, THE ARGUMENT 1721 * IS TWO'S COMPLIMENTED. IF THE ABSOLUTE VALUE OF THE ARGUMENT 1722 * IS GREATER THAN OR EQUAL TO FLOATING POINT ONE, THE IDENTITY, 1723 * ATN(X)=PI/2+ATN(-1/X), IS APPLIED. THE REDUCED ARGUMENT IS SAVED 1724 * AND THEN SQUARED. THE POLYNOMIAL IS EVALUATED IN THE REDUCED ARGU- 1725 * MENT SQUARED WITH THE FOLLOWING COEFFICIENTS: C0=1, C1=-.3333315, 1726 * C2=.1999355, C3=-.142089, C4=.1065626, C5=-.07528964, 1727 * C6=.04296961, C7=-.01616574, C8=.002866226. THE POLYNOMIAL RESULT 1728 * IS MULTIPL1ED BY THE REDUCED ARGUMENT. IF THE ABSOLUTE VALUE OF 1729 * THE ORIGINAL ARGUMENT WAS GREATER THAN OR EQUAL TO ZERO, THE SCALE 1730 * FACTOR FLAG WILL BE MINUS ONE. WHEN IT IS 'IRS'ED A SKIP WILL 1731 * OCCUR CAUSING PI/2 TO BE ADDED TO THE RESULT. THE SIGN FLAG IS 1732 * THEN 'IRS'ED, AND IF THE ORIGINAL ARGUMENT WAS POSITIVE, THERE WILL BE 1733 * A SKIP. OTHERWISE THE RESULT IS TWO'S COMPLIMENTED. 1734 * 1735 * 1736 01411 0 000000 ATNF DAC ** ENTRY 1737 01412 0 02 01503 LDA M2 1738 01413 0 04 00650 STA CTMP INITIALIZE SIGN FLAG AND 1739 01414 0 04 01502 STA SFAC SCALE FACTOR FLAG TO MINUS TWO 1740 01415 0 02 01411 LDA ATNF 1741 01416 0 10 00070 JST LARG LOAD THE ARGUMENT 1742 01417 101400 SMI 1743 01420 0 12 00650 IRS CTMP IF POSITIVE, INCREMENT THE SIGN FLAG 1744 01421 100400 SPL 1745 01422 0 10 00122 JST N$22 IF NEGATIVE, TWO'S COMPLIMENT 1746 01423 0 11 01144 CAS F1 COMPARE WITH ONE 1747 01424 101000 NOP 1748 01425 0 01 01446 JMP AT01 IF GREATER OR EQUAL, JUMP TO REDUCE 1749 * THE ARGUMENT 1750 01426 0 10 00104 AT02 JST H$22 SAVE THE REDUCED ARGUMENT AS Z2 1751 01427 0 001170 DAC Z2 1752 01430 0 10 00530 JST M$22 SQUARE IT 1753 01431 0 001170 DAC Z2 1754 01432 0 10 01172 JST FPLY EVALUATE THE POLYNOMIAL IN THE REDICED 1755 01433 0 001500 DAC AT03 ARGUMENT SQUARED 1756 01434 0 10 00530 JST M$22 MULTIPLY RESULT BY THE REDUCED ARGUMENT