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Coding for Interviews: Bit Manipulation
<body>
<p>Decimal: <input type="text" id="txtDecimal" value="5"><input type="submit" id="btnGoDecimal" value="Go"></p>
<p>Binary (MSB first): <input type="text" id="txtBinary" value="101"><input type="submit" id="btnGoBinary" value="Go"></p>
<p>
Bit position (LSB is zero): <input type="number" id="numBit" value="0" min="0" max="128"><input type="submit" id="btnGet" value="Get">
<input type="submit" id="btnSet0" value="Set to 0"><input type="submit" id="btnSet1" value="Set to 1">
</p>
<p id="pResult"></p>
</body>
window.onload = function() {
var myNumber;
var toBinary = function (number) {
var bitArray = [];
while (number > 0) {
bitArray.push(number % 2);
number >>= 1;
}
bitArray.reverse();
return bitArray;
};
var toDecimal = function(bitArray) {
var decimal = 0;
for (var i = 0; i < bitArray.length; ++i) {
decimal += bitArray[i]*Math.pow(2, bitArray.length-1-i);
}
return decimal;
};
var getBit = function(number, index) {
var mask = (1 << index);
//
// TODO: operator precedence matters
//
return (number & mask) > 0 ? 1 : 0;
};
var setBit = function(number, index, set) {
var mask = 1 << index;
return set ? number | mask : number & (~mask);
};
var goDecimal = function() {
var inputStr = $("#txtDecimal").val();
if (!inputStr.match(RegExp("^-?[0-9]+$"))) {
alert("Please enter an integer in decimal, without leading zeros.");
return;
}
var inputNum = parseInt(inputStr);
if (inputNum <= 0) {
alert("Please enter a positive integer.");
return;
}
myNumber = inputNum;
$("#txtBinary").val(toBinary(inputNum).join(""));
};
goDecimal();
$("#btnGoDecimal").click(goDecimal);
$("#btnGoBinary").click(function() {
var inputStr = $("#txtBinary").val();
if (!inputStr.match(RegExp("^[01]+$"))) {
alert("Please enter an integer in binary, without separators.");
return;
}
var bitArray = [];
for (var i = 0; i < inputStr.length; ++i) {
bitArray.push(inputStr[i] == 1 ? 1 : 0);
}
myNumber = toDecimal(bitArray);
$("#txtDecimal").val(myNumber);
});
$("#btnGet").click(function() {
var idx = parseInt($("#numBit").val());
$("#pResult").html("Bit is " + (getBit(myNumber, idx) ? "on" : "off"));
});
$("#btnSet0").click(function() {
var idx = parseInt($("#numBit").val());
myNumber = setBit(myNumber, idx, 0);
$("#txtDecimal").val(myNumber);
$("#txtBinary").val(toBinary(myNumber).join(""));
$("#pResult").html("");
});
$("#btnSet1").click(function() {
var idx = parseInt($("#numBit").val());
myNumber = setBit(myNumber, idx, 1);
$("#txtDecimal").val(myNumber);
$("#txtBinary").val(toBinary(myNumber).join(""));
$("#pResult").html("");
});
}
name: Bit twiddling
description: Some description, please keep it in one line
authors:
- Michael Penkov
normalize_css: no
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