Add reading/writing of floats and doubles from/to buffers

Code for readIEEE754/writeIEEE754 is from jspack: http://code.google.com/p/jspack/

1 files changed, 118 insertions, 0 deletions

diff --git a/lib/buffer_ieee754.js b/lib/buffer_ieee754.js
new file mode 100644
index 0000000000..5d2af613b9
--- /dev/null
+++ b/lib/buffer_ieee754.js
@@ -0,0 +1,118 @@
+// Copyright (c) 2008, Fair Oaks Labs, Inc.
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+// 
+//  * Redistributions of source code must retain the above copyright notice,
+//    this list of conditions and the following disclaimer.
+// 
+//  * Redistributions in binary form must reproduce the above copyright notice,
+//    this list of conditions and the following disclaimer in the documentation
+//    and/or other materials provided with the distribution.
+// 
+//  * 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.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+//
+// 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;
+};