Spectrum ROM: Routine at 36AF

The address of this routine is found in the table of addresses. It is called via the calculator literal +27 by the routines at BEEP, FP_TO_BC, LOG_2_A, PRINT_FP, n_mod_m, exp and get_argt. It is also called indirectly via fp_calc_2.

This subroutine handles the function INT X and returns a 'last value' that is the 'integer part' of the value supplied. Thus INT 2.4 gives 2 but as the subroutine always rounds the result down INT -2.4 gives -3.

The subroutine uses truncate to produce I(X) such that I(2.4)=2 and I(-2.4)=-2. Thus, INT X is given by I(X) when X>=0, and by I(X)-1 for negative values of X that are not already integers, when the result is, of course, I(X).

The address of this routine is found in the table of addresses. It is called via the calculator literal +27 by the routines at BEEP, FP_TO_BC, LOG_2_A, PRINT_FP, n_mod_m, exp and get_argt. It is also called indirectly via fp_calc_2. This subroutine handles the function INT X and returns a 'last value' that is the 'integer part' of the value supplied. Thus INT 2.4 gives 2 but as the subroutine always rounds the result down INT -2.4 gives -3. The subroutine uses truncate to produce I(X) such that I(2.4)=2 and I(-2.4)=-2. Thus, INT X is given by I(X) when X>=0, and by I(X)-1 for negative values of X that are not already integers, when the result is, of course, I(X).
int	36AF	RST $28	X
	36B0	DEFB $31	duplicate: X, X
	36B1	DEFB $36	less_0: X, (1/0)
	36B2	DEFB $00	jump_true to X_NEG: X
	36B3	DEFB $04	jump_true to X_NEG: X
For values of X that have been shown to be greater than or equal to zero there is no jump and I(X) is readily found.
	36B4	DEFB $3A	truncate: I(X)
	36B5	DEFB $38	end_calc
	36B6	RET	Finished.
When X is a negative integer I(X) is returned, otherwise I(X)-1 is returned.
X_NEG	36B7	DEFB $31	duplicate: X, X
	36B8	DEFB $3A	truncate: X, I(X)
	36B9	DEFB $C0	st_mem_0: X, I(X) (mem-0 holds I(X))
	36BA	DEFB $03	subtract: X-I(X)
	36BB	DEFB $E0	get_mem_0: X-I(X), I(X)
	36BC	DEFB $01	exchange: I(X), X-I(X)
	36BD	DEFB $30	f_not: I(X), (1/0)
	36BE	DEFB $00	jump_true to EXIT: I(X)
	36BF	DEFB $03	jump_true to EXIT: I(X)
The jump is made for values of X that are negative integers, otherwise there is no jump and I(X)-1 is calculated.
	36C0	DEFB $A1	stk_one: I(X), 1
	36C1	DEFB $03	subtract: I(X)-1
In either case the subroutine finishes with:
EXIT	36C2	DEFB $38	end_calc: I(X) or I(X)-1
	36C3	RET