Bug 154725 – [DFG] DFG ArithRound for non-zero-case is incorrect for negative numbers in x86

• Component: JavaScriptCore
• Status: RESOLVED DUPLICATE

[Yusuke Suzuki]

We use branchTruncateDoubleToInt32, it emits cvttsd2si_rr.
But its rounding mode is not floor.

The test case is the following.

function mathRoundDoesNotCareAboutMinusZero(value)
{
    return Math.round(value)|0;
}
noInline(mathRoundDoesNotCareAboutMinusZero);

for (var i = 0; i < 1e4; ++i) {
    var doubleMid = -9901 - 0.6;
    var roundedValue = mathRoundDoesNotCareAboutMinusZero(doubleMid);
    print(doubleMid, roundedValue);
    if (roundedValue !== -9902)
        throw "mathRoundDoesNotCareAboutMinusZero(" + doubleMid + ") = " + roundedValue;
}

[Yusuke Suzuki]

If we can use SSE 4.2 roundss, we should do that (It takes rounding mode!)

[Yusuke Suzuki]

I'll fix this with https://bugs.webkit.org/show_bug.cgi?id=154683

*** This bug has been marked as a duplicate of bug 154683 ***