Created attachment 645875 [details] [diff] [review] don't use == with float layout/generic/nsTextFrameThebes.cpp currently has some equality comparison with float point. While it looks like they should be valid in a really strict compiler, on x86 there can be some problems. The x87 stack has higher precision than a float. If one side of the comparison is coming from a computation on the stack and the other one is loaded from memory, there can be a small difference that causes the comparison to fail.
A try push is at https://tbpl.mozilla.org/?tree=Try&pusher=respindola@mozilla.com.
Comment on attachment 645875 [details] [diff] [review] don't use == with float Review of attachment 645875 [details] [diff] [review]: ----------------------------------------------------------------- ::: layout/generic/nsTextFrameThebes.cpp @@ +6710,5 @@ > } > } > > +bool nsTextFrame::IsCurrentFontInflation(float aInflation) const { > + return fabsf(aInflation - GetFontSizeInflation()) < 1e-6; If aInflation is greater than 1e6 * epsilon, which is roughly 1e+1, then this is no different than the == comparison it replaces. So: - either you know something very specific here about the order of magnitude of aInflation? - or you should use a relative (multiplicative), not absolute, fuzzy comparison. Typically: abs(a - b) < precision * min(abs(a), abs(b))
From what I see in the code, the comparison is always used to check if a value is from a previous call to GetFontSizeInflation. The case I noticed it failing was because one side had been stored (narrowed to a float) and the other wasn't. The difference from the long double to the float was about 1e-8, so I just used 1e-6, but I agree it is not a general solution. Do we have a routine for relative comparison somewhere in the codebase?
Font inflation values will generally be between 0.1 and 10 so this is fine.
btw, gcc >= 3.0 has a -Wfloat-equal warning flag that will warn when a floating point value is compared for equality using the == or != operators. http://gcc.gnu.org/onlinedocs/gcc-3.0.4/gcc_3.html#SEC11
https://hg.mozilla.org/mozilla-central/rev/05852ba29df2
(In reply to Chris Peterson (:cpeterson) from comment #5) > btw, gcc >= 3.0 has a -Wfloat-equal warning flag that will warn when a > floating point value is compared for equality using the == or != operators. > > http://gcc.gnu.org/onlinedocs/gcc-3.0.4/gcc_3.html#SEC11 Filed bug 777803 to enable this warning.
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