Bug 7748 – toPrecision sometimes messes up the last digit on intel Macs

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Maciej Stachowiak]

The JSC implementation of Number.toPrecision sometimes gets a different last digit on intel Macs than on PowerPC Macs or non-Mac intel systems. This is most likely due to a bug in the system pow() function. Nevertheless, I have a patch that works around it by directly coding computation of integer powers of 10.

[Maciej Stachowiak]

Created attachment 7040 [details]
fix by adding intPow10 function

I only replaced toPrecision's use of pow(10.0, n) with intPow10(n). Should I do the same for toExponential and toFixed (even though we have not yet spotted a specific bug with those)? I am guessing they will face the same problem with pow()'s bad rounding of powers of 10.

[Darin Adler]

Comment on attachment 7040 [details]
fix by adding intPow10 function

-          e = static_cast<int>(log10(x));
+          e = static_cast<int>(trunc(log10(x)));

Why that change? Does trunc add value? Why trunc and not floor?

+	      n = floor(x / tens);

Looks like there's a tab in the patch.

r=me

[Maciej Stachowiak]

Finally landed this.