[CHORE] add IEEE-754 Double Precision float support

for an 8 byte representation of floats

src/js/ripple/ieee754.js

@@ -0,0 +1,107 @@
+// Convert a JavaScript number to IEEE-754 Double Precision
+// value represented as an array of 8 bytes (octets)
+//
+// Based on:
+// http://cautionsingularityahead.blogspot.com/2010/04/javascript-and-ieee754-redux.html
+//
+// Found and modified from:
+// https://gist.github.com/bartaz/1119041
+
+var Float = exports.Float = {};
+
+Float.toIEEE754 = function(v, ebits, fbits) {
+
+  var bias = (1 << (ebits - 1)) - 1;
+
+  // Compute sign, exponent, fraction
+  var s, e, f;
+  if (isNaN(v)) {
+    e = (1 << bias) - 1; f = 1; s = 0;
+  }
+  else if (v === Infinity || v === -Infinity) {
+    e = (1 << bias) - 1; f = 0; s = (v < 0) ? 1 : 0;
+  }
+  else if (v === 0) {
+    e = 0; f = 0; s = (1 / v === -Infinity) ? 1 : 0;
+  }
+  else {
+    s = v < 0;
+    v = Math.abs(v);
+
+    if (v >= Math.pow(2, 1 - bias)) {
+      var ln = Math.min(Math.floor(Math.log(v) / Math.LN2), bias);
+      e = ln + bias;
+      f = v * Math.pow(2, fbits - ln) - Math.pow(2, fbits);
+    }
+    else {
+      e = 0;
+      f = v / Math.pow(2, 1 - bias - fbits);
+    }
+  }
+
+  // Pack sign, exponent, fraction
+  var i, bits = [];
+  for (i = fbits; i; i -= 1) { bits.push(f % 2 ? 1 : 0); f = Math.floor(f / 2); }
+  for (i = ebits; i; i -= 1) { bits.push(e % 2 ? 1 : 0); e = Math.floor(e / 2); }
+  bits.push(s ? 1 : 0);
+  bits.reverse();
+  var str = bits.join('');
+
+  // Bits to bytes
+  var bytes = [];
+  while (str.length) {
+    bytes.push(parseInt(str.substring(0, 8), 2));
+    str = str.substring(8);
+  }
+  return bytes;
+}
+
+Float.fromIEEE754 = function(bytes, ebits, fbits) {
+
+  // Bytes to bits
+  var bits = [];
+  for (var i = bytes.length; i; i -= 1) {
+    var byte = bytes[i - 1];
+    for (var j = 8; j; j -= 1) {
+      bits.push(byte % 2 ? 1 : 0); byte = byte >> 1;
+    }
+  }
+  bits.reverse();
+  var str = bits.join('');
+
+  // Unpack sign, exponent, fraction
+  var bias = (1 << (ebits - 1)) - 1;
+  var s = parseInt(str.substring(0, 1), 2) ? -1 : 1;
+  var e = parseInt(str.substring(1, 1 + ebits), 2);
+  var f = parseInt(str.substring(1 + ebits), 2);
+
+  // Produce number
+  if (e === (1 << ebits) - 1) {
+    return f !== 0 ? NaN : s * Infinity;
+  }
+  else if (e > 0) {
+    return s * Math.pow(2, e - bias) * (1 + f / Math.pow(2, fbits));
+  }
+  else if (f !== 0) {
+    return s * Math.pow(2, -(bias-1)) * (f / Math.pow(2, fbits));
+  }
+  else {
+    return s * 0;
+  }
+}
+
+Float.fromIEEE754Double = function(b) { return Float.fromIEEE754(b, 11, 52); }
+Float.toIEEE754Double = function(v) { return   Float.toIEEE754(v, 11, 52); }
+Float.fromIEEE754Single = function(b) { return Float.fromIEEE754(b,  8, 23); }
+Float.toIEEE754Single = function(v) { return   Float.toIEEE754(v,  8, 23); }
+
+
+// Convert array of octets to string binary representation
+// by bartaz
+
+Float.toIEEE754DoubleString = function(v) {
+  return exports.toIEEE754Double(v)
+    .map(function(n){ for(n = n.toString(2);n.length < 8;n="0"+n); return n })
+    .join('')
+    .replace(/(.)(.{11})(.{52})/, "$1 $2 $3")
+}