#!/usr/bin/env jsish
/* 4 bit adder simulation, in Jsish */
function not(a) { return a == 1 ? 0 : 1; }
function and(a, b) { return a + b < 2 ? 0 : 1; }
function nand(a, b) { return not(and(a, b)); }
function or(a, b) { return nand(nand(a,a), nand(b,b)); }
function xor(a, b) { return nand(nand(nand(a,b), a), nand(nand(a,b), b)); }

function halfAdder(a, b) { return { carry: and(a, b), sum: xor(a, b) }; }
function fullAdder(a, b, c) {
    var h0 = halfAdder(a, b),
        h1 = halfAdder(h0.sum, c);
    return {carry: or(h0.carry, h1.carry), sum: h1.sum };
}

function fourBitAdder(a, b) {
    // set to width 4, pad with 0 if too short and truncate right if too long
    var inA = Array(4),
        inB = Array(4),
        out = Array(4),
        i = 4,
        pass;

    if (a.length < 4) a = '0'.repeat(4 - a.length) + a;
    a = a.slice(-4);
    if (b.length < 4) b = '0'.repeat(4 - b.length) + b;
    b = b.slice(-4);
    while (i--) {
        var re = /0|1/;
        if (a[i] && !re.test(a[i])) throw('bad bit at a[' + i + '] of ' + quote(a[i]));
        if (b[i] && !re.test(b[i])) throw('bad bit at b[' + i + '] of ' + quote(b[i]));
        inA[i] = a[i] != 1 ? 0 : 1;
        inB[i] = b[i] != 1 ? 0 : 1;
    }

    printf('%s + %s = ', a, b);

    // now we can start adding... connecting the constructive blocks
    pass = halfAdder(inA[3], inB[3]);
    out[3] = pass.sum;
    pass = fullAdder(inA[2], inB[2], pass.carry);
    out[2] = pass.sum;
    pass = fullAdder(inA[1], inB[1], pass.carry);
    out[1] = pass.sum;
    pass = fullAdder(inA[0], inB[0], pass.carry);
    out[0] = pass.sum;

    var result = parseInt(pass.carry + out.join(''), 2);
    printf('%s  %d\n', out.join('') + ' carry ' + pass.carry, result);
    return result;
}

if (Interp.conf('unitTest')) {
    var bits = [['0000', '0000'], ['0000', '0001'], ['1000', '0001'],
                ['1010', '0101'], ['1000', '1000'], ['1100', '1100'],
                ['1111', '1111']];
    for (var pair of bits) {
        fourBitAdder(pair[0], pair[1]);
    }
;   fourBitAdder('1', '11');
;   fourBitAdder('10001', '01110');
;// fourBitAdder('0002', 'b');
}

/*
=!EXPECTSTART!=
0000 + 0000 = 0000 carry 0  0
0000 + 0001 = 0001 carry 0  1
1000 + 0001 = 1001 carry 0  9
1010 + 0101 = 1111 carry 0  15
1000 + 1000 = 0000 carry 1  16
1100 + 1100 = 1000 carry 1  24
1111 + 1111 = 1110 carry 1  30
fourBitAdder('1', '11') ==> 0001 + 0011 = 0100 carry 0  4
4
fourBitAdder('10001', '01110') ==> 0001 + 1110 = 1111 carry 0  15
15
fourBitAdder('0002', 'b') ==>
PASS!: err = bad bit at a[3] of "2"
=!EXPECTEND!=
*/