1907936 - ClampDoubleToUint8 incorrectly rounds towards 0

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect, P1)

Description

[André Bargull [:anba]]

Previously reported at bug 745324. The patch attached to bug 745324 is incomplete and doesn't correctly handle the case when the fractional part is .5.

Comment 1

[André Bargull [:anba]]

Attachment: Bug 1907936: Correctly implement RoundHalfToEven in ClampDoubleToUint8. r=jandem!

There are various ways how to implement half-to-even rounding, this C++
implementation was choosen because it's easy to translate into assembly
instructions.

• Update the x86 implementation to use half-to-even rounding when available.
• Use a single unified implementation for ARM32, because I didn't want to
  spend time trying to make sense of the HasVFPv3 code path which uses
  fixed floating point values.
• ARM64 doesn't need any changes, because it was already using Fcvtns, which
  implements half-to-even rounding.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/e6d1732365c6
Correctly implement RoundHalfToEven in ClampDoubleToUint8. r=jandem

Comment 3

[Serban Stanca [:SerbanS]]

https://hg.mozilla.org/mozilla-central/rev/e6d1732365c6