goog-varint.ts

// Copyright 2008 Google Inc.  All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Code generated by the Protocol Buffer compiler is owned by the owner
// of the input file used when generating it.  This code is not
// standalone and requires a support library to be linked with it.  This
// support library is itself covered by the above license.


/**
 * Read a 64 bit varint as two JS numbers.
 *
 * Returns tuple:
 * [0]: low bits
 * [0]: high bits
 *
 * Copyright 2008 Google Inc.  All rights reserved.
 *
 * See https://github.com/protocolbuffers/protobuf/blob/8a71927d74a4ce34efe2d8769fda198f52d20d12/js/experimental/runtime/kernel/buffer_decoder.js#L175
 */
export function varint64read(this: ReaderLike): [number, number] {
    let lowBits = 0;
    let highBits = 0;

    for (let shift = 0; shift < 28; shift += 7) {
        let b = this.buf[this.pos++];
        lowBits |= (b & 0x7F) << shift;
        if ((b & 0x80) == 0) {
            this.assertBounds();
            return [lowBits, highBits];
        }
    }

    let middleByte = this.buf[this.pos++];

    // last four bits of the first 32 bit number
    lowBits |= (middleByte & 0x0F) << 28;

    // 3 upper bits are part of the next 32 bit number
    highBits = (middleByte & 0x70) >> 4;

    if ((middleByte & 0x80) == 0) {
        this.assertBounds();
        return [lowBits, highBits];
    }

    for (let shift = 3; shift <= 31; shift += 7) {
        let b = this.buf[this.pos++];
        highBits |= (b & 0x7F) << shift;
        if ((b & 0x80) == 0) {
            this.assertBounds();
            return [lowBits, highBits];
        }
    }

    throw new Error('invalid varint');
}



/**
 * Write a 64 bit varint, given as two JS numbers, to the given bytes array.
 *
 * Copyright 2008 Google Inc.  All rights reserved.
 *
 * See https://github.com/protocolbuffers/protobuf/blob/8a71927d74a4ce34efe2d8769fda198f52d20d12/js/experimental/runtime/kernel/writer.js#L344
 */
export function varint64write(lo: number, hi: number, bytes: number[]): void {
    for (let i = 0; i < 28; i = i + 7) {
        const shift = lo >>> i;
        const hasNext = !((shift >>> 7) == 0 && hi == 0);
        const byte = (hasNext ? shift | 0x80 : shift) & 0xFF;
        bytes.push(byte);
        if (!hasNext) {
            return;
        }
    }

    const splitBits = ((lo >>> 28) & 0x0F) | ((hi & 0x07) << 4);
    const hasMoreBits = !((hi >> 3) == 0);
    bytes.push(
        (hasMoreBits ? splitBits | 0x80 : splitBits) & 0xFF);

    if (!hasMoreBits) {
        return;
    }

    for (let i = 3; i < 31; i = i + 7) {
        const shift = hi >>> i;
        const hasNext = !((shift >>> 7) == 0);
        const byte = (hasNext ? shift | 0x80 : shift) & 0xFF;
        bytes.push(byte);
        if (!hasNext) {
            return;
        }
    }

    bytes.push((hi >>> 31) & 0x01);
}

// constants for binary math
const TWO_PWR_32_DBL = (1 << 16) * (1 << 16);


/**
 * Parse decimal string of 64 bit integer value as two JS numbers.
 *
 * Returns tuple:
 * [0]: minus sign?
 * [1]: low bits
 * [2]: high bits
 *
 * Copyright 2008 Google Inc.
 */
export function int64fromString(dec: string): [boolean, number, number] {
    // Check for minus sign.
    let minus = dec[0] == '-';
    if (minus)
        dec = dec.slice(1);
    // Work 6 decimal digits at a time, acting like we're converting base 1e6
    // digits to binary. This is safe to do with floating point math because
    // Number.isSafeInteger(ALL_32_BITS * 1e6) == true.
    const base = 1e6;
    let lowBits = 0;
    let highBits = 0;

    function add1e6digit(begin: number, end?: number) {
        // Note: Number('') is 0.
        const digit1e6 = Number(dec.slice(begin, end));
        highBits *= base;
        lowBits = lowBits * base + digit1e6;
        // Carry bits from lowBits to highBits
        if (lowBits >= TWO_PWR_32_DBL) {
            highBits = highBits + ((lowBits / TWO_PWR_32_DBL) | 0);
            lowBits = lowBits % TWO_PWR_32_DBL;
        }
    }

    add1e6digit(-24, -18);
    add1e6digit(-18, -12);
    add1e6digit(-12, -6);
    add1e6digit(-6);
    return [minus, lowBits, highBits];
}


/**
 * Format 64 bit integer value (as two JS numbers) to decimal string.
 *
 * Copyright 2008 Google Inc.
 */
export function int64toString(bitsLow: number, bitsHigh: number): string {
    // Skip the expensive conversion if the number is small enough to use the
    // built-in conversions.
    if ((bitsHigh >>> 0) <= 0x1FFFFF) {
        return '' + (TWO_PWR_32_DBL * bitsHigh + (bitsLow >>> 0));
    }

    // What this code is doing is essentially converting the input number from
    // base-2 to base-1e7, which allows us to represent the 64-bit range with
    // only 3 (very large) digits. Those digits are then trivial to convert to
    // a base-10 string.

    // The magic numbers used here are -
    // 2^24 = 16777216 = (1,6777216) in base-1e7.
    // 2^48 = 281474976710656 = (2,8147497,6710656) in base-1e7.

    // Split 32:32 representation into 16:24:24 representation so our
    // intermediate digits don't overflow.
    let low = bitsLow & 0xFFFFFF;
    let mid = (((bitsLow >>> 24) | (bitsHigh << 8)) >>> 0) & 0xFFFFFF;
    let high = (bitsHigh >> 16) & 0xFFFF;

    // Assemble our three base-1e7 digits, ignoring carries. The maximum
    // value in a digit at this step is representable as a 48-bit integer, which
    // can be stored in a 64-bit floating point number.
    let digitA = low + (mid * 6777216) + (high * 6710656);
    let digitB = mid + (high * 8147497);
    let digitC = (high * 2);

    // Apply carries from A to B and from B to C.
    let base = 10000000;
    if (digitA >= base) {
        digitB += Math.floor(digitA / base);
        digitA %= base;
    }

    if (digitB >= base) {
        digitC += Math.floor(digitB / base);
        digitB %= base;
    }

    // Convert base-1e7 digits to base-10, with optional leading zeroes.
    function decimalFrom1e7(digit1e7: number, needLeadingZeros: number) {
        let partial = digit1e7 ? String(digit1e7) : '';
        if (needLeadingZeros) {
            return '0000000'.slice(partial.length) + partial;
        }
        return partial;
    }

    return decimalFrom1e7(digitC, /*needLeadingZeros=*/ 0) +
        decimalFrom1e7(digitB, /*needLeadingZeros=*/ digitC) +
        // If the final 1e7 digit didn't need leading zeros, we would have
        // returned via the trivial code path at the top.
        decimalFrom1e7(digitA, /*needLeadingZeros=*/ 1);
}


/**
 * Write a 32 bit varint, signed or unsigned. Same as `varint64write(0, value, bytes)`
 *
 * Copyright 2008 Google Inc.  All rights reserved.
 *
 * See https://github.com/protocolbuffers/protobuf/blob/1b18833f4f2a2f681f4e4a25cdf3b0a43115ec26/js/binary/encoder.js#L144
 */
export function varint32write(value: number, bytes: number[]): void {
    if (value >= 0) {
        // write value as varint 32
        while (value > 0x7f) {
            bytes.push((value & 0x7f) | 0x80);
            value = value >>> 7;
        }
        bytes.push(value);
    } else {
        for (let i = 0; i < 9; i++) {
            bytes.push(value & 127 | 128);
            value = value >> 7;
        }
        bytes.push(1);
    }
}


/**
 * Read an unsigned 32 bit varint.
 *
 * See https://github.com/protocolbuffers/protobuf/blob/8a71927d74a4ce34efe2d8769fda198f52d20d12/js/experimental/runtime/kernel/buffer_decoder.js#L220
 */
export function varint32read(this: ReaderLike): number {

    let b = this.buf[this.pos++];
    let result = b & 0x7F;
    if ((b & 0x80) == 0) {
        this.assertBounds();
        return result;
    }

    b = this.buf[this.pos++];
    result |= (b & 0x7F) << 7;
    if ((b & 0x80) == 0){
        this.assertBounds();
        return result;
    }

    b = this.buf[this.pos++];
    result |= (b & 0x7F) << 14;
    if ((b & 0x80) == 0){
        this.assertBounds();
        return result;
    }

    b = this.buf[this.pos++];
    result |= (b & 0x7F) << 21;
    if ((b & 0x80) == 0){
        this.assertBounds();
        return result;
    }

    // Extract only last 4 bits
    b = this.buf[this.pos++];
    result |= (b & 0x0F) << 28;

    for (let readBytes = 5; ((b & 0x80) !== 0) && readBytes < 10; readBytes++)
        b = this.buf[this.pos++];

    if ((b & 0x80) != 0)
        throw new Error('invalid varint');

    this.assertBounds();

    // Result can have 32 bits, convert it to unsigned
    return result >>> 0;
}


type ReaderLike = {
    buf: Uint8Array;
    pos: number;
    len: number;
    assertBounds(): void;
}