Spectrum ROM: Routine at 14387

The address of this routine is found in the table of addresses. It is called via the calculator literal 34 by the routine at acs. It is also called indirectly via fp_calc_2.

This subroutine handles the function ASN X and returns a real number from -π/2 to π/2 inclusive which is equal to the value in radians of the angle whose sine is X. Thereby if Y=ASN X then X=SIN Y.

This subroutine uses the trigonometric identity TAN (Y/2)=SIN Y/(1+COS Y) to obtain TAN (Y/2) and hence (using ATN) Y/2 and finally Y.

The address of this routine is found in the table of addresses. It is called via the calculator literal 34 by the routine at acs. It is also called indirectly via fp_calc_2. This subroutine handles the function ASN X and returns a real number from -π/2 to π/2 inclusive which is equal to the value in radians of the angle whose sine is X. Thereby if Y=ASN X then X=SIN Y. This subroutine uses the trigonometric identity TAN (Y/2)=SIN Y/(1+COS Y) to obtain TAN (Y/2) and hence (using ATN) Y/2 and finally Y.
asn	14387	RST 40	X
	14388	DEFB 49	duplicate: X, X
	14389	DEFB 49	duplicate: X, X, X
	14390	DEFB 4	multiply: X, X*X
	14391	DEFB 161	stk_one: X, X*X, 1
	14392	DEFB 3	subtract: X, X*X-1
	14393	DEFB 27	negate: X, 1-X*X
	14394	DEFB 40	sqr: X, SQR (1-X*X)
	14395	DEFB 161	stk_one: X, SQR (1-X*X), 1
	14396	DEFB 15	addition: X, 1+SQR (1-X*X)
	14397	DEFB 5	division: X/(1+SQR (1-X*X))=TAN (Y/2)
	14398	DEFB 36	atn: Y/2
	14399	DEFB 49	duplicate: Y/2, Y/2
	14400	DEFB 15	addition: Y=ASN X
	14401	DEFB 56	end_calc
	14402	RET	Finished: 'last value'=ASN X.