websnark/tools/buildwitness.js

const assert = require("assert");

function writeUint32(h, val) {
    h.dataView.setUint32(h.offset, val, true);
    h.offset += 4;
}


function writeBigInt(h, bi) {
    for (let i=0; i<8; i++) {
        const v = bi.shiftRight(i*32).and(0xFFFFFFFF).toJSNumber();
        writeUint32(h, v);
    }
}


function calculateBuffLen(witness) {
    let size = 0;

    // beta2, delta2
    size += witness.length * 32;

    return size;
}


function buildWitness(witness) {
    const buffLen = calculateBuffLen(witness);

    const buff = new ArrayBuffer(buffLen);

    const h = {
        dataView: new DataView(buff),
        offset: 0
    };

    // writeUint32(h, witness.length);

    for (let i=0; i<witness.length; i++) {
        writeBigInt(h, witness[i]);
    }

    assert.equal(h.offset, buffLen);

    return Buffer.from(buff);
}

module.exports = buildWitness;