/*

* Copyright (c) 2022 RethinkDNS and its authors.

*

* This Source Code Form is subject to the terms of the Mozilla Public

* License, v. 2.0. If a copy of the MPL was not distributed with this

* file, You can obtain one at http://mozilla.org/MPL/2.0/.

*/

import { W, bufferView } from "./config.js";

import { MaskTop } from "./bufreader.js";

/**

* The BitWriter will create a stream of bytes, letting you write a certain

* number of bits at a time. This is part of the encoder, so it is not

* optimized for memory or speed.

*/

export function BitWriter() {

this.init();

}

BitWriter.prototype = {

init: function () {

this.bits = [];

this.bytes = [];

this.bits16 = [];

this.top = 0;

},

write16(data, numBits) {

// todo: throw error?

if (numBits > 16) {

log.e("writes upto 16 lsb bits; out of range: " + numBits);

return;

}

const n = data;

const brim = 16 - (this.top % 16);

const cur = (this.top / 16) | 0;

const e = this.bits16[cur] | 0;

let remainingBits = 0;

// clear msb

let b = n & MaskTop[16][16 - numBits];

// shift to bit pos to be right at brim-th bit

if (brim >= numBits) {

b = b << (brim - numBits);

} else {

// shave right most bits if there are too many bits than

// what the current element at the brim can accomodate

remainingBits = numBits - brim;

b = b >>> remainingBits;

}

// overlay b on current element, e.

b = e | b;

this.bits16[cur] = b;

// account for the left-over bits shaved off by brim

if (remainingBits > 0) {

b = n & MaskTop[16][16 - remainingBits];

b = b << (16 - remainingBits);

this.bits16[cur + 1] = b;

}

// update top to reflect the bits included

this.top += numBits;

},

/**

* Write some data to the bit string; number(bits) <= 32.

*/

write: function (data, numBits) {

while (numBits > 0) {

// take 16 and then the leftover pass it to write16

const i = ((numBits - 1) / 16) | 0;

const b = data >>> (i * 16);

const l = numBits % 16 === 0 ? 16 : numBits % 16;

this.write16(b, l);

numBits -= l;

}

return;

},

getData: function () {

return this.bitsToBytes();

},

/**

* Get the bitstring represented as a javascript string of bytes

*/

bitsToBytes: function () {

return bufferView[W].from(this.bits16);

},

};