frequency conversion

var convert = function () {
														document.getElementById("result").innerHTML = 
															"<font face=\"Geneva, Arial, Helvetica, sans-serif\">" +
															frequencyToNote() + "</font>";
													}
													
													var frequencyToNote = function () {
														var input = Number(document.getElementById("frequency").value);
														if(isNaN(input) || (input == 0))
															return "<font color=\"red\">Enter a numerical value for frequency</font>";
														if((input < 27.5) || (input > 14080))
															return "<font color=\"red\">Enter a frequency in the range 27.5Hz (A0) and 14080Hz (A9)</font>";
														
														var A4 = 440.0;
														var A4_INDEX = 57;
												
														var notes = [
															"C0","C#0","D0","D#0","E0","F0","F#0","G0","G#0","A0","A#0","B0",
															"C1","C#1","D1","D#1","E1","F1","F#1","G1","G#1","A1","A#1","B1",
															"C2","C#2","D2","D#2","E2","F2","F#2","G2","G#2","A2","A#2","B2",
															"C3","C#3","D3","D#3","E3","F3","F#3","G3","G#3","A3","A#3","B3",
															"C4","C#4","D4","D#4","E4","F4","F#4","G4","G#4","A4","A#4","B4",
															"C5","C#5","D5","D#5","E5","F5","F#5","G5","G#5","A5","A#5","B5",
															"C6","C#6","D6","D#6","E6","F6","F#6","G6","G#6","A6","A#6","B6",
															"C7","C#7","D7","D#7","E7","F7","F#7","G7","G#7","A7","A#7","B7",
															"C8","C#8","D8","D#8","E8","F8","F#8","G8","G#8","A8","A#8","B8",
															"C9","C#9","D9","D#9","E9","F9","F#9","G9","G#9","A9","A#9","B9" ];
												
														var MINUS = 0;
														var PLUS = 1;
														
														var frequency;
														var r = Math.pow(2.0, 1.0/12.0);
														var cent = Math.pow(2.0, 1.0/1200.0);
														var r_index = 0;
														var cent_index = 0;
														var side;  
												
														frequency = A4;
													
														if(input >= frequency) {
															while(input >= r*frequency) {
																frequency = r*frequency;
																r_index++;
															}
															while(input > cent*frequency) {
																frequency = cent*frequency;
																cent_index++;
															}
															if((cent*frequency - input) < (input - frequency))
																cent_index++;
															if(cent_index > 50) {
																r_index++;
																cent_index = 100 - cent_index;
																if(cent_index != 0)
																	side = MINUS;
																else
																	side = PLUS;
															}
															else
																side = PLUS;
														}
													
														else {
															while(input <= frequency/r) {
																frequency = frequency/r;
																r_index--;
															}
															while(input < frequency/cent) {
																frequency = frequency/cent;
																cent_index++;
															}
															if((input - frequency/cent) < (frequency - input))
																cent_index++;
															if(cent_index >= 50) {
																r_index--;
																cent_index = 100 - cent_index;
																side = PLUS;
															}
															else {
																if(cent_index != 0)
																	side = MINUS;
																else
																	side = PLUS;
															}  
														}
													
														var result = notes[A4_INDEX + r_index];
														if(side == PLUS)
															result = result + " plus ";
														else
															result = result + " minus ";
														result = result + cent_index + " cents";
														return result;
													}