SupremeTechnopriest/whitney-buffers

export function read (buffer, offset, mLen, nBytes) {
  let e, m
  const eLen = nBytes * 8 - mLen - 1
  const eMax = (1 << eLen) - 1
  const eBias = eMax >> 1
  let nBits = -7
  let i = (nBytes - 1)
  const d = -1
  let s = buffer[offset + i]

  i += d

  e = s & ((1 << (-nBits)) - 1)
  s >>= (-nBits)
  nBits += eLen
  for (; nBits > 0; e = e * 256 + buffer[offset + i], i += d, nBits -= 8) {}

  m = e & ((1 << (-nBits)) - 1)
  e >>= (-nBits)
  nBits += mLen
  for (; nBits > 0; m = m * 256 + buffer[offset + i], i += d, nBits -= 8) {}

  if (e === 0) {
    e = 1 - eBias
  } else if (e === eMax) {
    return m ? NaN : ((s ? -1 : 1) * Infinity)
  } else {
    m = m + Math.pow(2, mLen)
    e = e - eBias
  }
  return (s ? -1 : 1) * m * Math.pow(2, e - mLen)
}

export function write (buffer, value, offset, mLen, nBytes) {
  let e, m, c
  let eLen = nBytes * 8 - mLen - 1
  const eMax = (1 << eLen) - 1
  const eBias = eMax >> 1
  const rt = (mLen === 23 ? Math.pow(2, -24) - Math.pow(2, -77) : 0)
  let i = 0
  const d = 1
  const s = value < 0 || (value === 0 && 1 / value < 0) ? 1 : 0

  value = Math.abs(value)

  if (isNaN(value) || value === Infinity) {
    m = isNaN(value) ? 1 : 0
    e = eMax
  } else {
    e = Math.floor(Math.log(value) / Math.LN2)
    if (value * (c = Math.pow(2, -e)) < 1) {
      e--
      c *= 2
    }
    if (e + eBias >= 1) {
      value += rt / c
    } else {
      value += rt * Math.pow(2, 1 - eBias)
    }
    if (value * c >= 2) {
      e++
      c /= 2
    }

    if (e + eBias >= eMax) {
      m = 0
      e = eMax
    } else if (e + eBias >= 1) {
      m = (value * c - 1) * Math.pow(2, mLen)
      e = e + eBias
    } else {
      m = value * Math.pow(2, eBias - 1) * Math.pow(2, mLen)
      e = 0
    }
  }

  for (; mLen >= 8; buffer[offset + i] = m & 0xff, i += d, m /= 256, mLen -= 8) {}

  e = (e << mLen) | m
  eLen += mLen
  for (; eLen > 0; buffer[offset + i] = e & 0xff, i += d, e /= 256, eLen -= 8) {}

  buffer[offset + i - d] |= s * 128
}

export default { read, write }