capnp-ts/src/types/int64.ts

Strongly typed Cap'n Proto implementation for the browser and Node.js using TypeScript

/**
 * @author jdiaz5513
 */

import initTrace from "debug";

import { MAX_SAFE_INTEGER, VAL32 } from "../constants";
import { pad } from "../util";
import { Uint64 } from "./uint64";

const trace = initTrace("capnp:int64");
trace("load");

/**
 * Represents a signed 64-bit integer stored using a Uint8Array in little-endian format.
 *
 * You may convert this to a primitive number by calling `toNumber()` but be wary of precision loss!
 *
 * The value passed in as the source buffer is expected to be in little-endian format.
 */

export class Int64 extends Uint64 {
  static fromArrayBuffer(source: ArrayBuffer, offset = 0, noCopy = false): Int64 {
    if (noCopy) return new this(new Uint8Array(source, offset, 8));

    return new this(new Uint8Array(source.slice(offset, offset + 8)));
  }

  static fromDataView(source: DataView, offset = 0, noCopy = false): Int64 {
    if (noCopy) {
      return new this(new Uint8Array(source.buffer, source.byteOffset + offset, 8));
    }

    return new this(new Uint8Array(source.buffer.slice(source.byteOffset + offset, source.byteLength + offset + 8)));
  }

  static fromNumber(source: number): Int64 {
    const ret = new this(new Uint8Array(8));

    ret.setValue(source);

    return ret;
  }

  /**
   * Parse a hexadecimal string in **big endian format** as an Int64 value.
   *
   * The value will be negative if the string is either preceded with a `-` sign, or already in the negative 2's
   * complement form.
   *
   * @static
   * @param {string} source The source string.
   * @returns {Int64} The string parsed as a 64-bit signed integer.
   */

  static fromHexString(source: string): Int64 {
    if (source.substr(0, 2) === "0x") source = source.substr(2);

    if (source.length < 1) return Int64.fromNumber(0);

    const neg = source[0] === "-";

    if (neg) source = source.substr(1);

    source = pad(source, 16);

    if (source.length !== 16) {
      throw new RangeError("Source string must contain at most 16 hexadecimal digits.");
    }

    const bytes = source.toLowerCase().replace(/[^\da-f]/g, "");
    const buf = new Uint8Array(new ArrayBuffer(8));

    for (let i = 0; i < 8; i++) {
      buf[7 - i] = parseInt(bytes.substr(i * 2, 2), 16);
    }

    const val = new Int64(buf);

    if (neg) val.negate();

    return val;
  }

  static fromUint8Array(source: Uint8Array, offset = 0, noCopy = false): Int64 {
    if (noCopy) return new this(source.subarray(offset, offset + 8));

    return new this(new Uint8Array(source.buffer.slice(source.byteOffset + offset, source.byteOffset + offset + 8)));
  }

  equals(other: Int64): boolean {
    return super.equals(other);
  }

  inspect(): string {
    return `[Int64 ${this.toString(10)} 0x${this.toHexString()}]`;
  }

  negate(): void {
    for (let b = this.buffer, carry = 1, i = 0; i < 8; i++) {
      const v = (b[i] ^ 0xff) + carry;

      b[i] = v & 0xff;
      carry = v >> 8;
    }
  }

  setValue(loWord: number, hiWord?: number): void {
    let negate = false;
    let lo = loWord;
    let hi = hiWord;

    if (hi === undefined) {
      hi = lo;
      negate = hi < 0;
      hi = Math.abs(hi);
      lo = hi % VAL32;
      hi = hi / VAL32;

      if (hi > VAL32) throw new RangeError(`${loWord} is outside Int64 range`);

      hi = hi >>> 0;
    }

    for (let i = 0; i < 8; i++) {
      this.buffer[i] = lo & 0xff;

      lo = i === 3 ? hi : lo >>> 8;
    }

    if (negate) this.negate();
  }

  toHexString(): string {
    const b = this.buffer;
    const negate = b[7] & 0x80;

    if (negate) this.negate();

    let hex = "";

    for (let i = 7; i >= 0; i--) {
      let v = b[i].toString(16);

      if (v.length === 1) v = "0" + v;

      hex += v;
    }

    if (negate) {
      this.negate();

      hex = "-" + hex;
    }

    return hex;
  }

  /**
   * Convert to a native javascript number.
   *
   * WARNING: do not expect this number to be accurate to integer precision for large (positive or negative) numbers!
   *
   * @param {boolean} allowImprecise If `true`, no check is performed to verify the returned value is accurate;
   * otherwise out-of-range values are clamped to +/-Infinity.
   * @returns {number} A numeric representation of this integer.
   */

  toNumber(allowImprecise?: boolean): number {
    const b = this.buffer;
    const negate = b[7] & 0x80;

    let x = 0;
    let carry = 1;
    let i = 0;
    let m = 1;

    while (i < 8) {
      let v = b[i];

      if (negate) {
        v = (v ^ 0xff) + carry;
        carry = v >> 8;
        v = v & 0xff;
      }

      x += v * m;
      m *= 256;
      i++;
    }

    if (!allowImprecise && x >= MAX_SAFE_INTEGER) {
      trace("Coercing out of range value %d to Infinity.", x);

      return negate ? -Infinity : Infinity;
    }

    return negate ? -x : x;
  }
}