Second Chapter

Half adder

carry=進位值

CHIP HalfAdder {
    IN a, b;    // 1-bit inputs
    OUT sum,    // Right bit of a + b 
        carry;  // Left bit of a + b

    PARTS:
    Xor(a=a,b=b,out=sum);
    And(a=a,b=b,out=carry);
}

Full adder

CHIP FullAdder {
    IN a, b, c;  // 1-bit inputs
    OUT sum,     // Right bit of a + b + c
        carry;   // Left bit of a + b + c
    PARTS:
    Xor(a=a,b=b,out=ab);
    Xor(a=ab,b=c,out=sum);
    And(a=ab,b=c,out=abc);
    And(a=a,b=b,out=aandb);
    Or(a=aandb,b=abc,out=carry);
}

Add16

//最低位用半加器，因為不需要考慮來自低位的進位。

CHIP Add16 {
    IN a[16], b[16];
    OUT out[16];

    PARTS:
    HalfAdder(a=a[0], b=b[0], sum=out[0], carry=c0);
    FullAdder(a=a[1], b=b[1], c=c0, sum=out[1], carry=c1);
    FullAdder(a=a[2], b=b[2], c=c1, sum=out[2], carry=c2);
    FullAdder(a=a[3], b=b[3], c=c2, sum=out[3], carry=c3);
    FullAdder(a=a[4], b=b[4], c=c3, sum=out[4], carry=c4);
    FullAdder(a=a[5], b=b[5], c=c4, sum=out[5], carry=c5);
    FullAdder(a=a[6], b=b[6], c=c5, sum=out[6], carry=c6);
    FullAdder(a=a[7], b=b[7], c=c6, sum=out[7], carry=c7);
    FullAdder(a=a[8], b=b[8], c=c7, sum=out[8], carry=c8);
    FullAdder(a=a[9], b=b[9], c=c8, sum=out[9], carry=c9);
    FullAdder(a=a[10], b=b[10], c=c9, sum=out[10], carry=c10);
    FullAdder(a=a[11], b=b[11], c=c10, sum=out[11], carry=c11);
    FullAdder(a=a[12], b=b[12], c=c11, sum=out[12], carry=c12);
    FullAdder(a=a[13], b=b[13], c=c12, sum=out[13], carry=c13);
    FullAdder(a=a[14], b=b[14], c=c13, sum=out[14], carry=c14);
    FullAdder(a=a[15], b=b[15], c=c14, sum=out[15], carry=ignored);
}

Inc16

完成16－bit的自加1

CHIP Inc16 {
    IN in[16];
    OUT out[16];

    PARTS:
    Add16(a=in,b[0]=true,out=out);
}

ALU

CHIP ALU {
    IN  
        x[16], y[16],  // 16-bit inputs        
        zx, // zero the x input?
        nx, // negate the x input?
        zy, // zero the y input?
        ny, // negate the y input?
        f,  // compute out = x + y (if 1) or x & y (if 0)
        no; // negate the out output?

    OUT 
        out[16], // 16-bit output
        zr, // 1 if (out == 0), 0 otherwise
        ng; // 1 if (out < 0),  0 otherwise

    PARTS:
    Mux16(a=x,b=false,sel=zx,out=muxx);
    Not16(in=muxx,out=notx);
    Mux16(a=muxx,b=notx,sel=nx,out=mnx);

    Mux16(a=y,b=false,sel=zy,out=muxy);
    Not16(in=muxy,out=noty);
    Mux16(a=muxy,b=noty,sel=ny,out=mny);

    And16(a=mnx,b=mny,out=andxy);
    Add16(a=mnx,b=mny,out=addxy);

    Mux16(a=andxy,b=addxy,sel=f,out=outa);
    Not16(in=outa,out=nout);
    Mux16(a=outa,b=nout,sel=no,out=o1);
    And16(a=outa,b=nout,out[0..7]=outLow,out[8..15]=outHigh);
    Or8Way(in=outLow,out=orLow);
    Or8Way(in=outHigh,out=orHigh);
    Or(a=orLow, b=orHigh, out=notzr);
    Not(in=notzr, out=zr);    
    And16(a=o1,b=o1,out[15]=ng);
    And16(a=o1,b=o1,out=out);

    }