1380031 - Math.E not equal to Math.exp(1)

Status: RESOLVED FIXED

(Core :: JavaScript: Standard Library, defect, P3)

Description

[Seth]

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0
Build ID: 20170628075643

Steps to reproduce:

The constant Math.E (The number e) should be the same as Math.exp(1) (e^1=e), but Math.exp(1) has an extra (wrong) digit. Math.E is correct to 15 decimal places, Math.exp(1) has 16 decimal places, and the 16th digit is a 5, but the correct 16th digit would be 2. This leads to the unexpected result of Math.E being unequal to Math.exp(1)

console.log(Math.E, Math.exp(1), Math.E===Math.exp(1));


Actual results:

2.718281828459045, 2.7182818284590455, false


Expected results:

2.718281828459045, 2.718281828459045, true

It works as expected in Google's web browser.

Comment 1

[André Bargull [:anba]]

Interesting: https://github.com/v8/v8/blob/4a03a23565315c4558b4ba003b25c6869b8366e7/src/base/ieee754.cc#L1543-L1547

Comment 2

[Tooru Fujisawa [:arai]]

now we're using imported fdlibm's exp function, and looks like the issue doesn't happen before fdlibm (bug 933257), at least on macOS 10.12.5.
we could either switch to system exp function or apply the same fix as v8.

Comment 3

[André Bargull [:anba]]

Hmm, I think it makes sense to apply the same fix as V8 did, because that way we don't have to worry about platform differences, which could be an issue if the system exp function is used.

Comment 4

[Jim Mathies [:jimm]]

P3, unassigned -> fix optional for 57

Comment 5

[André Bargull [:anba]]

Attachment: Bug 1380031: Ensure Math.exp(1) returns Math.E. r=arai!

Comment 6

[André Bargull [:anba]]

Try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=6d1b93f0792688a2ee8f68c13951ae53b4cff2a2

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/0808c449b015
Ensure Math.exp(1) returns Math.E. r=arai

Comment 8

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/0808c449b015

Comment 9

[Peter Van der Beken [:peterv]]

https://hg.mozilla.org/projects/ash/rev/0808c449b0156fc7adbdddba77f4a1d2eff11040
Bug 1380031: Ensure Math.exp(1) returns Math.E. r=arai