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36AF: THE 'INT' FUNCTION (offset +27)
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).
Input
Output
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
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
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
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