Spectrum ROM: Routine at 3851

The address of this routine is found in the table of addresses. It is called indirectly via fp_calc_2, and the routine at sqr continues here.

This subroutine performs the binary operation of raising the first number, X, to the power of the second number, Y.

The subroutine treats the result X**Y as being equivalent to EXP (Y*LN X). It returns this value unless X is zero, in which case it returns 1 if Y is also zero (0**0=1), returns zero if Y is positive, and reports arithmetic overflow if Y is negative.

The address of this routine is found in the table of addresses. It is called indirectly via fp_calc_2, and the routine at sqr continues here. This subroutine performs the binary operation of raising the first number, X, to the power of the second number, Y. The subroutine treats the result X*Y as being equivalent to EXP (YLN X). It returns this value unless X is zero, in which case it returns 1 if Y is also zero (0**0=1), returns zero if Y is positive, and reports arithmetic overflow if Y is negative.
to_power	3851	RST $28	X, Y
	3852	DEFB $01	exchange: Y, X
	3853	DEFB $31	duplicate: Y, X, X
	3854	DEFB $30	f_not: Y, X, (1/0)
	3855	DEFB $00	jump_true to XIS0: Y, X
	3856	DEFB $07	jump_true to XIS0: Y, X
The jump is made if X=0, otherwise EXP (Y*LN X) is formed.
	3857	DEFB $25	ln: Y, LN X
Giving report A if X is negative.
	3858	DEFB $04	multiply: Y*LN X
	3859	DEFB $38	end_calc
	385A	JP exp	Exit via exp to form EXP (Y*LN X).
The value of X is zero so consider the three possible cases involved.
XIS0	385D	DEFB $02	delete: Y
	385E	DEFB $31	duplicate: Y, Y
	385F	DEFB $30	f_not: Y, (1/0)
	3860	DEFB $00	jump_true to ONE: Y
	3861	DEFB $09	jump_true to ONE: Y
The jump is made if X=0 and Y=0, otherwise proceed.
	3862	DEFB $A0	stk_zero: Y, 0
	3863	DEFB $01	exchange: 0, Y
	3864	DEFB $37	greater_0: 0, (1/0)
	3865	DEFB $00	jump_true to LAST: 0
	3866	DEFB $06	jump_true to LAST: 0
The jump is made if X=0 and Y is positive, otherwise proceed.
	3867	DEFB $A1	stk_one: 0, 1
	3868	DEFB $01	exchange: 1, 0
	3869	DEFB $05	division: Exit via division as dividing by zero gives 'arithmetic overflow'.
The result is to be 1 for the operation.
ONE	386A	DEFB $02	delete: -
	386B	DEFB $A1	stk_one: 1
Now return with the 'last value' on the stack being 0**Y.
LAST	386C	DEFB $38	end_calc: (1/0)
	386D	RET	Finished: 'last value' is 0 or 1.