I am trying without much success to convert a very large hex number to decimal. My problem is that using deciaml = parseInt(hex, 16) gives me errors in the number when I try to convert a hex number above 14 digits.
I have no problem with this in Java, but Javascript does not seem to be accurate above 14 digits of hex.
I have tried "BigNumber" but tis gives me the same erroneous result.
I have trawled the web to the best of my ability and found web sites that will do the conversion but cannot figure out how to do the conversion longhand.
I have tried getting each character in turn and multiplying it by its factor i.e. 123456789abcdef 15 * Math.pow(16, 0) + 14 * Math.pow(16, 1).... etc but I think (being a noob) that my subroutines may not hev been all they should be because I got a completely (and I mean really different!) answer.
If it helps you guys I can post what I have written so far for you to look at but I am hoping someone has simple answer for me.
<script>
function Hex2decimal(hex){
var stringLength = hex.length;
var characterPosition = stringLength;
var character;
var hexChars = new Array();
hexChars[0] = "0";
hexChars[1] = "1";
hexChars[2] = "2";
hexChars[3] = "3";
hexChars[4] = "4";
hexChars[5] = "5";
hexChars[6] = "6";
hexChars[7] = "7";
hexChars[8] = "8";
hexChars[9] = "9";
hexChars[10] = "a";
hexChars[11] = "b";
hexChars[12] = "c";
hexChars[13] = "d";
hexChars[14] = "e";
hexChars[15] = "f";
var index = 0;
var hexChar;
var result;
// document.writeln(hex);
while (characterPosition >= 0)
{
// document.writeln(characterPosition);
character = hex.charAt(characterPosition);
while (index < hexChars.length)
{
// document.writeln(index);
document.writeln("String Character = " + character);
hexChar = hexChars[index];
document.writeln("Hex Character = " + hexChar);
if (hexChar == character)
{
result = hexChar;
document.writeln(result);
}
index++
}
// document.write(character);
characterPosition--;
}
return result;
}
</script>
Thank you.
Paul
Ok, let's try this:
function h2d(s) {
function add(x, y) {
var c = 0, r = [];
var x = x.split('').map(Number);
var y = y.split('').map(Number);
while(x.length || y.length) {
var s = (x.pop() || 0) + (y.pop() || 0) + c;
r.unshift(s < 10 ? s : s - 10);
c = s < 10 ? 0 : 1;
}
if(c) r.unshift(c);
return r.join('');
}
var dec = '0';
s.split('').forEach(function(chr) {
var n = parseInt(chr, 16);
for(var t = 8; t; t >>= 1) {
dec = add(dec, dec);
if(n & t) dec = add(dec, '1');
}
});
return dec;
}
Test:
t = 'dfae267ab6e87c62b10b476e0d70b06f8378802d21f34e7'
console.log(h2d(t))
prints
342789023478234789127089427304981273408912349586345899239
which is correct (feel free to verify).
var hex = "7FDDDDDDDDDDDDDDDDDDDDDD";
if (hex.length % 2) { hex = '0' + hex; }
var bn = BigInt('0x' + hex);
var d = bn.toString(10);
BigInt
s are now available in most browsers (except IE).
Earlier in this answer:
BigInt
s are now available in both node.js and Chrome. Firefox shouldn't be far behind.If you need to deal with negative numbers, that requires a bit of work:
Essentially:
function hexToBn(hex) {
if (hex.length % 2) {
hex = '0' + hex;
}
var highbyte = parseInt(hex.slice(0, 2), 16)
var bn = BigInt('0x' + hex);
if (0x80 & highbyte) {
// You'd think `bn = ~bn;` would work... but it doesn't
// manually perform two's compliment (flip bits, add one)
// (because JS binary operators are incorrect for negatives)
bn = BigInt('0b' + bn.toString(2).split('').map(function (i) {
return '0' === i ? 1 : 0
}).join('')) + BigInt(1);
bn = -bn;
}
return bn;
}
Notice that "0x" + "ff" will be considered as 255, so convert your hex value to a string and add "0x" ahead.
function Hex2decimal(hex)
{
return ("0x" + hex) / 1;
}
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