function toFrac( frac ) {
	var sum = 0;
	var i;
	for ( i = 0; i < frac.length; i++ ) {
		if ( frac[ i ] === '1' ) {
			sum += pow( 2.0, -(i+1) );
		}
	}
	return sum;
}
Converts a float's fraction bit sequence to a numeric value.

@private
@param {BinaryString} frac - literal bit representation of a float's fraction bit sequence
@returns {number} fraction value

@example
var v = toFrac( '10001100010111110011000' );
// returns ~0.548

@example
var v = toFrac( '11110101000101011111111' );
// returns ~0.957