1const bn128 = require("snarkjs").bn128;
 2const bigInt = require("snarkjs").bigInt;
 3const Web3Utils = require("web3-utils");
 4const F = bn128.Fr;
 5
 6const SEED = "mimcsponge";
 7const NROUNDS = 220;
 8
 9exports.getIV = (seed) => {
10    if (typeof seed === "undefined") seed = SEED;
11    const c = Web3Utils.keccak256(seed+"_iv");
12    const cn = bigInt(Web3Utils.toBN(c).toString());
13    const iv = cn.mod(F.q);
14    return iv;
15};
16
17exports.getConstants = (seed, nRounds) => {
18    if (typeof seed === "undefined") seed = SEED;
19    if (typeof nRounds === "undefined") nRounds = NROUNDS;
20    const cts = new Array(nRounds);
21    let c = Web3Utils.keccak256(SEED);
22    for (let i=1; i<nRounds; i++) {
23        c = Web3Utils.keccak256(c);
24
25        const n1 = Web3Utils.toBN(c).mod(Web3Utils.toBN(F.q.toString()));
26        const c2 = Web3Utils.padLeft(Web3Utils.toHex(n1), 64);
27        cts[i] = bigInt(Web3Utils.toBN(c2).toString());
28    }
29    cts[0] = bigInt(0);
30    cts[cts.length - 1] = bigInt(0);
31    return cts;
32};
33
34const cts = exports.getConstants(SEED, NROUNDS);
35
36exports.hash = (_xL_in, _xR_in, _k) =>{
37    let xL = bigInt(_xL_in);
38    let xR = bigInt(_xR_in);
39    const k = bigInt(_k);
40    for (let i=0; i<NROUNDS; i++) {
41        const c = cts[i];
42        const t = (i==0) ? F.add(xL, k) : F.add(F.add(xL, k), c);
43        const xR_tmp = bigInt(xR);
44        if (i < (NROUNDS - 1)) {
45          xR = xL;
46          xL = F.add(xR_tmp, F.exp(t, 5));
47        } else {
48          xR = F.add(xR_tmp, F.exp(t, 5));
49        }
50    }
51    return {
52      xL: F.affine(xL),
53      xR: F.affine(xR),
54    };
55};
56
57exports.multiHash = (arr, key, numOutputs) => {
58    if (typeof(numOutputs) === "undefined") {
59      numOutputs = 1;
60    }
61    if (typeof(key) === "undefined") {
62        key = F.zero;
63    }
64
65    let R = F.zero;
66    let C = F.zero;
67
68    for (let i=0; i<arr.length; i++) {
69      R = F.add(R, bigInt(arr[i]));
70      const S = exports.hash(R, C, key);
71      R = S.xL;
72      C = S.xR;
73    }
74    let outputs = [R];
75    for (let i=1; i < numOutputs; i++) {
76      const S = exports.hash(R, C, key);
77      R = S.xL;
78      C = S.xR;
79      outputs.push(R);
80    }
81    if (numOutputs == 1) {
82      return F.affine(outputs[0]);
83    } else {
84      return outputs.map(x => F.affine(x));
85    }
86};