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float.js

A little mirror class for introspecting the bit-patterns of JS numbers using typed arrays.

Example:

Math.PI.introspect().mantissa;     //             "1001001000011111101101010100010001000010110100011000"
Math.E.introspect().exponent;      //  "10000000000"
(9.0).introspect().toBitString();  // "0100000000100010000000000000000000000000000000000000000000000000"
(-Math.PI).introspect().negative;  // true

Interactively explore at http://dherman.github.com/float.js.

How it works

Internally, this puts the number in a single-element Float64Array typed array and gets its buffer to read the value’s raw bits:

(new Float64Array([n])).buffer

Then it converts that buffer to a string of "1"s and "0"s by viewing the buffer as a Uint8Array and mapping each viewed byte to a binary string with .toString(2). Finally, it creates properties like exponent and mantissa by using [] array indexing, .substring, and .slice to extract the relevant bits.

License

Copyright © 2012 Dave Herman

Licensed under the MIT License.