buffer_ieee754.js

// Copyright (c) 2008, Fair Oaks Labs, Inc.
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//    this list of conditions and the following disclaimer.
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//  * Neither the name of Fair Oaks Labs, Inc. nor the names of its contributors
//    may be used to endorse or promote products derived from this software
//    without specific prior written permission.
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// Modifications to writeIEEE754 to support negative zeroes made by Brian White

exports.readIEEE754 = function(buffer, offset, endian, mLen, nBytes) {
  var e, m,
      bBE = (endian === 'big'),
      eLen = nBytes * 8 - mLen - 1,
      eMax = (1 << eLen) - 1,
      eBias = eMax >> 1,
      nBits = -7,
      i = bBE ? 0 : (nBytes - 1),
      d = bBE ? 1 : -1,
      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);
};

exports.writeIEEE754 = function(buffer, value, offset, endian, mLen, nBytes) {
  var e, m, c,
      bBE = (endian === 'big'),
      eLen = nBytes * 8 - mLen - 1,
      eMax = (1 << eLen) - 1,
      eBias = eMax >> 1,
      rt = (mLen === 23 ? Math.pow(2, -24) - Math.pow(2, -77) : 0),
      i = bBE ? (nBytes-1) : 0,
      d = bBE ? -1 : 1,
      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;
};