borc/src/utils.js

Encode and parse data in the Concise Binary Object Representation (CBOR) data format (RFC7049).

'use strict'

const { Buffer } = require('buffer')
const Bignumber = require('bignumber.js').BigNumber

const constants = require('./constants')
const SHIFT32 = constants.SHIFT32
const SHIFT16 = constants.SHIFT16
const MAX_SAFE_HIGH = 0x1fffff

exports.parseHalf = function parseHalf (buf) {
  const sign = buf[0] & 0x80 ? -1 : 1
  const exp = (buf[0] & 0x7C) >> 2
  const mant = ((buf[0] & 0x03) << 8) | buf[1]
  if (!exp) {
    return sign * 5.9604644775390625e-8 * mant
  } else if (exp === 0x1f) {
    return sign * (mant ? 0 / 0 : 2e308) // eslint-disable-line no-loss-of-precision
  } else {
    return sign * Math.pow(2, exp - 25) * (1024 + mant)
  }
}

function toHex (n) {
  if (n < 16) {
    return '0' + n.toString(16)
  }

  return n.toString(16)
}

exports.arrayBufferToBignumber = function (buf) {
  const len = buf.byteLength
  let res = ''
  for (let i = 0; i < len; i++) {
    res += toHex(buf[i])
  }

  return new Bignumber(res, 16)
}

// convert an Object into a Map
exports.buildMap = (obj) => {
  const res = new Map()
  const keys = Object.keys(obj)
  const length = keys.length
  for (let i = 0; i < length; i++) {
    res.set(keys[i], obj[keys[i]])
  }
  return res
}

exports.buildInt32 = (f, g) => {
  return f * SHIFT16 + g
}

exports.buildInt64 = (f1, f2, g1, g2) => {
  const f = exports.buildInt32(f1, f2)
  const g = exports.buildInt32(g1, g2)

  if (f > MAX_SAFE_HIGH) {
    return new Bignumber(f).times(SHIFT32).plus(g)
  } else {
    return (f * SHIFT32) + g
  }
}

exports.writeHalf = function writeHalf (buf, half) {
  // assume 0, -0, NaN, Infinity, and -Infinity have already been caught

  // HACK: everyone settle in.  This isn't going to be pretty.
  // Translate cn-cbor's C code (from Carsten Borman):

  // uint32_t be32;
  // uint16_t be16, u16;
  // union {
  //   float f;
  //   uint32_t u;
  // } u32;
  // u32.f = float_val;

  const u32 = Buffer.allocUnsafe(4)
  u32.writeFloatBE(half, 0)
  const u = u32.readUInt32BE(0)

  // if ((u32.u & 0x1FFF) == 0) { /* worth trying half */

  // hildjj: If the lower 13 bits are 0, we won't lose anything in the conversion
  if ((u & 0x1FFF) !== 0) {
    return false
  }

  //   int s16 = (u32.u >> 16) & 0x8000;
  //   int exp = (u32.u >> 23) & 0xff;
  //   int mant = u32.u & 0x7fffff;

  let s16 = (u >> 16) & 0x8000 // top bit is sign
  const exp = (u >> 23) & 0xff // then 5 bits of exponent
  const mant = u & 0x7fffff

  //   if (exp == 0 && mant == 0)
  //     ;              /* 0.0, -0.0 */

  // hildjj: zeros already handled.  Assert if you don't believe me.

  //   else if (exp >= 113 && exp <= 142) /* normalized */
  //     s16 += ((exp - 112) << 10) + (mant >> 13);
  if ((exp >= 113) && (exp <= 142)) {
    s16 += ((exp - 112) << 10) + (mant >> 13)

  //   else if (exp >= 103 && exp < 113) { /* denorm, exp16 = 0 */
  //     if (mant & ((1 << (126 - exp)) - 1))
  //       goto float32;         /* loss of precision */
  //     s16 += ((mant + 0x800000) >> (126 - exp));
  } else if ((exp >= 103) && (exp < 113)) {
    if (mant & ((1 << (126 - exp)) - 1)) {
      return false
    }
    s16 += ((mant + 0x800000) >> (126 - exp))

    //   } else if (exp == 255 && mant == 0) { /* Inf */
    //     s16 += 0x7c00;

    // hildjj: Infinity already handled

  //   } else
  //     goto float32;           /* loss of range */
  } else {
    return false
  }

  //   ensure_writable(3);
  //   u16 = s16;
  //   be16 = hton16p((const uint8_t*)&u16);
  buf.writeUInt16BE(s16, 0)
  return true
}

exports.keySorter = function (a, b) {
  const lenA = a[0].byteLength
  const lenB = b[0].byteLength

  if (lenA > lenB) {
    return 1
  }

  if (lenB > lenA) {
    return -1
  }

  return a[0].compare(b[0])
}

// Adapted from http://www.2ality.com/2012/03/signedzero.html
exports.isNegativeZero = (x) => {
  return x === 0 && (1 / x < 0)
}

exports.nextPowerOf2 = (n) => {
  let count = 0
  // First n in the below condition is for
  // the case where n is 0
  if (n && !(n & (n - 1))) {
    return n
  }

  while (n !== 0) {
    n >>= 1
    count += 1
  }

  return 1 << count
}