[Webkit-unassigned] [Bug 143457] New: Fix -Wparentheses warning with GCC 5 in SaturatedArithmetic.h

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=143457

            Bug ID: 143457
           Summary: Fix -Wparentheses warning with GCC 5 in
                    SaturatedArithmetic.h
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: Minor
          Priority: P2
         Component: Web Template Framework
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mcatanzaro at igalia.com

When building with GCC 5, I can't see any real warnings, because this buddy gets printed 3000 times [1] during compilation:

../../Source/WTF/wtf/SaturatedArithmetic.h: In function ‘bool signedAddOverflows(int32_t, int32_t, int32_t&)’:
../../Source/WTF/wtf/SaturatedArithmetic.h:49:29: warning: suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Wparentheses]
     return !((ua ^ ub) >> 31) & (uresult ^ ua) >> 31;
                             ^

Clang has had this same warning for a while. The warning is spurious [2], but it's a good warning so let's placate it rather than disable. Two solutions:

Add extra parentheses: return (!((ua ^ ub) >> 31)) & (uresult ^ ua) >> 31;

Note that is equivalent to the original code [3].

Another option is to use &&:

!((ua ^ ub) >> 31) && (uresult ^ ua) >> 31;

That looks better to me, since there are fewer parentheses and it avoids the confusing/unnecessary [3] mask.

[1] I just made that up, but it doesn't feel like an unreasonable guess.
[2] & and && both have the same precedence relative to !
[3] Provided I've squinted at this long enough.

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