Bug 200412 – Jitted code gives different floating point result

• Component: JavaScriptCore
• Status: NEW

[Vanessa Freudenberg]

Created attachment 375469 [details]
html and js demonstrating the bug

Example code (runnable at https://croquet.studio/static/math-bug.html):

    const pow = require("@stdlib/math/base/special/pow");
    window.StdlibMath = { pow };

    const func = () => window.StdlibMath.pow( 8.96096203115875, -0.6403121474522467 );

    console.log(func());

    let x = 0; for (let i = 0; i < 1000000; i++) x += func();

    console.log(func());

This code prints the same result twice if running in the Safari debugger, and on every other browser (Chrome, Firefox):
  0.24558156189439845
  0.24558156189439845
But the second result is different when run without debugger in Safari on Mac and iOS.
  0.24558156189439845
  0.24558156189439848
Re-running the code also sometimes prints a different second result randomly.

(we're using stdlib-js to avoid the built-in transcendental Math functions because we need deterministic results)

[Radar WebKit Bug Importer]

<rdar://problem/53919887>