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[/] [zipcpu/] [trunk/] [sw/] [lib/] [divs.S] - Blame information for rev 69

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Line No. Rev Author Line
1 45 dgisselq
;
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;       DIVS
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;
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;       Given R0,R1, computer R0 = R0/R1 and R1 = R0%R1 for signed R0,R1.
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;       We'll call R0 (input) x, R1(input) y, result is such that
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;       R0 * y + R1 = x.  Now let's work through our signs with an example
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;       where x = +/- 22, and y = +/- 4:
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;
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;       x y
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;       + +     No change, just call divu
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;       - +     (x=-22,y= 4,R0=-5,R1=-2)
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;       + -     (x= 22,y=-4,R0=-5,R1= 2)
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;       - -     (x=-22,y=-4,R0= 5,R1=-2)
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;
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;
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;
17 69 dgisselq
lib_divs: ; Given R0,R1, computer R0 = R0/R1 and R1 = R0%R1 for signed R0,R1
18 45 dgisselq
        SUB     2,SP
19 69 dgisselq
        STO     R2,(SP)
20 45 dgisselq
        STO     R3,2(SP)
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        ;
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        CLR     R3              ; Keep track of resulting sign in R2
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        TST     -1,R0           ; Is R0 negative?
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        MOV     ret_div32s(PC),R2
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        LLO.LT  3,R3            ; If so, resulting sign will be negative, and
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        NEG.LT  R0              ; then we negate R0 (R0 = ABS(R0))
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        MOV.LT  divu_divs_return(PC),R2
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        TST     -1,R1           ; Is R1 negative?
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        XOR.LT  1,R3            ; If so, result will be opposite sign of before
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        NEG.LT  R1              ; Now we get R1=ABS(R1)
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        MOV.LT  divu_divs_return(PC),R2
32 69 dgisselq
        BRA     lib_divu        ; Do our unsigned multiply
33 45 dgisselq
        ; JSR   divu            ; Do our unsigned multiply
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divu_divs_return:
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        TST     1,R3            ; Check resulting sign
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        NEG.NE  R0              ; Need to flip the sign of our result
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        TST     2,R3            ; Now, if R1 was originally negative
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        NEG.NE  R1              ; Then negate R1
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ret_div32s:
40 69 dgisselq
        LOD     (SP),R2
41 45 dgisselq
        LOD     2(SP),R3
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        ADD     2,SP
43 59 dgisselq
        JMP     R2
44 45 dgisselq
 

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