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An Anonymous Coward writes:

https://randomascii.wordpress.com/2020/09/27/floating-point-in-the-browser-part-1-impossible-expectations/ [wordpress.com]

A few years ago I did a lot of thinking and writing about floating-point math. It was good fun, and I learned a lot in the process, but sometimes I go a long time without actually using that hard-earned knowledge. So, I am always inordinately pleased when I end up working on a bug which requires some of that specialized knowledge. Here then is the first of (at least) three tales of floating-point bugs that I have investigated in Chromium. This is a short one.

Apparently the official JSON logo?The title of the bug was “JSON Parses 64-bit Integers Incorrectly”, which doesn’t immediately sound like a floating-point or browser issue, but it was filed in crbug.com and I was asked to take a look. The simplest version of the repro is to open the Chrome developer tools (F12 or Ctrl+Shift+I) and paste this code into the developer console:

        json = JSON.parse(‘{“x”: 2940078943461317278}’); alert(json[‘x’]);

Pasting unknown code into the console window is a good way to get pwned but this code was simple enough that I could tell that it wasn’t malicious. The bug report was nice enough to have included the author’s expectations and actual results:

        What is the expected behavior?
        The integer 2940078943461317278 should be returned.
        What went wrong?
        The integer 2940078943461317000 is returned instead.

Original Submission