varint.js

export function readVarintRemainder(l, s, p) {
    var buf = p.buf,
        h, b;

    b = buf[p.pos++]; h  = (b & 0x70) >> 4;  if (b < 0x80) return toNum(l, h, s);
    b = buf[p.pos++]; h |= (b & 0x7f) << 3;  if (b < 0x80) return toNum(l, h, s);
    b = buf[p.pos++]; h |= (b & 0x7f) << 10; if (b < 0x80) return toNum(l, h, s);
    b = buf[p.pos++]; h |= (b & 0x7f) << 17; if (b < 0x80) return toNum(l, h, s);
    b = buf[p.pos++]; h |= (b & 0x7f) << 24; if (b < 0x80) return toNum(l, h, s);
    b = buf[p.pos++]; h |= (b & 0x01) << 31; if (b < 0x80) return toNum(l, h, s);

    throw new Error('Expected varint not more than 10 bytes');
}

function toNum(low, high, isSigned) {
    if (isSigned) {
        return high * 0x100000000 + (low >>> 0);
    }

    return ((high >>> 0) * 0x100000000) + (low >>> 0);
}

export function writeBigVarint(val, pbf) {
    var low, high;

    if (val >= 0) {
        low  = (val % 0x100000000) | 0;
        high = (val / 0x100000000) | 0;
    } else {
        low  = ~(-val % 0x100000000);
        high = ~(-val / 0x100000000);

        if (low ^ 0xffffffff) {
            low = (low + 1) | 0;
        } else {
            low = 0;
            high = (high + 1) | 0;
        }
    }

    if (val >= 0x10000000000000000 || val < -0x10000000000000000) {
        throw new Error('Given varint doesn\'t fit into 10 bytes');
    }

    pbf.realloc(10);

    writeBigVarintLow(low, high, pbf);
    writeBigVarintHigh(high, pbf);
}

function writeBigVarintLow(low, high, pbf) {
    pbf.buf[pbf.pos++] = low & 0x7f | 0x80; low >>>= 7;
    pbf.buf[pbf.pos++] = low & 0x7f | 0x80; low >>>= 7;
    pbf.buf[pbf.pos++] = low & 0x7f | 0x80; low >>>= 7;
    pbf.buf[pbf.pos++] = low & 0x7f | 0x80; low >>>= 7;
    pbf.buf[pbf.pos]   = low & 0x7f;
}

function writeBigVarintHigh(high, pbf) {
    var lsb = (high & 0x07) << 4;

    pbf.buf[pbf.pos++] |= lsb         | ((high >>>= 3) ? 0x80 : 0); if (!high) return;
    pbf.buf[pbf.pos++]  = high & 0x7f | ((high >>>= 7) ? 0x80 : 0); if (!high) return;
    pbf.buf[pbf.pos++]  = high & 0x7f | ((high >>>= 7) ? 0x80 : 0); if (!high) return;
    pbf.buf[pbf.pos++]  = high & 0x7f | ((high >>>= 7) ? 0x80 : 0); if (!high) return;
    pbf.buf[pbf.pos++]  = high & 0x7f | ((high >>>= 7) ? 0x80 : 0); if (!high) return;
    pbf.buf[pbf.pos++]  = high & 0x7f;
}