Why isn't value obtained after Masking accurate in JavaScript?

Question

I was trying to extract last 32 bits from a Hex number in Javascript.

var hex = 0x6C469F301DBBC30;
var last32bit = (hex & 0xFFFFFFFF).toString(16);
log(last32bit); //gives 1dbbc40

The result is 1DBBC40. Shouldn't this supposed to be 1DBBC30 ? Also how do I preserve the 0 before 1DBBC40?

You could try `("00000000"+last32bit).slice(-8)` to preserve — mplungjan, Jul 02 '14 at 12:21
Thanks. That's a rough workaround I guess. But it'll serve my purpose. The filter is still inaccurate though. — Samik Sengupta, Jul 02 '14 at 12:23
Converting them to integers I get 487631152092003376 != 487631152092003392 — Samik Sengupta, Jul 02 '14 at 12:27
Converting them *how*? JavaScript does not represent numbers as integers. — Pointy, Jul 02 '14 at 12:27
If you've got the hex representation of the number, then you can extract the last 32 bits by working on that string representation of the value. — Pointy, Jul 02 '14 at 12:29
Well I did an online conversion of the numbers. I guess this cannot be handled accurately enough in JS. String method works accurately. I was just trying to do this mathematically. — Samik Sengupta, Jul 02 '14 at 12:29

score 3 · Accepted Answer · edited May 23 '17 at 10:26

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The ECMA standard says:

The Number type has exactly 18437736874454810627 (that is, 2⁶⁴−2⁵³+3) values

Your number is too large to be represented exactly by a Number. You should look for a big number library if you wish to accurately represent large numbers. Perhaps one of these libraries would meet your needs.

edited May 23 '17 at 10:26

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answered Jul 02 '14 at 12:26

Dark Falcon

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@SamikSengupta not with native JavaScript numeric facilities. – Pointy Jul 02 '14 at 12:28

Why isn't value obtained after Masking accurate in JavaScript?

1 Answers1