QkoSad
66 lines
2.3 KiB
Plaintext
Executable File
66 lines
2.3 KiB
Plaintext
Executable File
// This file is part of www.nand2tetris.org
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// and the book "The Elements of Computing Systems"
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// by Nisan and Schocken, MIT Press.
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// File name: projects/02/ALU.hdl
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/**
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* The ALU (Arithmetic Logic Unit).
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* Computes one of the following functions:
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* x+y, x-y, y-x, 0, 1, -1, x, y, -x, -y, !x, !y,
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* x+1, y+1, x-1, y-1, x&y, x|y on two 16-bit inputs,
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* according to 6 input bits denoted zx,nx,zy,ny,f,no.
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* In addition, the ALU computes two 1-bit outputs:
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* if the ALU output == 0, zr is set to 1; otherwise zr is set to 0;
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* if the ALU output < 0, ng is set to 1; otherwise ng is set to 0.
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*/
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// Implementation: the ALU logic manipulates the x and y inputs
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// and operates on the resulting values, as follows:
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// if (zx == 1) set x = 0 // 16-bit constant
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// if (nx == 1) set x = !x // bitwise not
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// if (zy == 1) set y = 0 // 16-bit constant
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// if (ny == 1) set y = !y // bitwise not
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// if (f == 1) set out = x + y // integer 2's complement addition
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// if (f == 0) set out = x & y // bitwise and
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// if (no == 1) set out = !out // bitwise not
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// if (out == 0) set zr = 1
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// if (out < 0) set ng = 1
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CHIP ALU {
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IN
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x[16], y[16], // 16-bit inputs
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zx, // zero the x input?
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nx, // negate the x input?
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zy, // zero the y input?
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ny, // negate the y input?
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f, // compute out = x + y (if 1) or x & y (if 0)
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no; // negate the out output?
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OUT
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out[16], // 16-bit output
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zr, // 1 if (out == 0), 0 otherwise
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ng; // 1 if (out < 0), 0 otherwise
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PARTS:
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Mux16(a=x,b[0..15]=false,sel=zx,out=outZx);//zx +
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Mux16(a=y,b[0..15]=false,sel=zy,out=outZy);//zy +
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Not16(in=outZx,out=outNx1);//nx1
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Not16(in=outZy,out=outNy1);//ny1
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Mux16(a=outZx,b=outNx1,sel=nx,out=outNx);//nx +
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Mux16(a=outZy,b=outNy1,sel=ny,out=outNy);//ny +
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Add16(a=outNx,b=outNy,out=outF1);//f1 +
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And16(a=outNy,b=outNx,out=outF0);//f0 +
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Mux16(a=outF0,b=outF1,sel=f,out=outF);//f
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Not16(in=outF,out=outNo1);//no +
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Mux16(a=outF, b=outNo1, sel=no, out=out, out[15]=ng, out[0..7]=zr1, out[8..15]=zr2); +
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Or8Way(in=zr1,out=out2);
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Or8Way(in=zr2,out=out3);
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Not(in=out2,out=out4);
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Not(in=out3,out=out5);
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And(a=out4,b=out5,out=zr);
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} |