[PATCH] Build fails to compile jchuff.c using gcc 4.5 on zLinux

[Adam Farley8]

Hi All,

If you compile jchuff.c (part of javajpeg) without 
"--disable-warnings-as-errors",
then you get an error that kills the build. This is seen in these 
circumstances:

Build: JDK9
gcc and g++ Version: 4.8.5
Platform: zLinux 64bit (s390x)

The error message is: 

/home/adamfarl/hotspot/jdk9/jdk/src/java.desktop/share/native/libjavajpeg/jchuff.c: 
In function 'jGenOptTbl':
/home/adamfarl/hotspot/jdk9/jdk/src/java.desktop/share/native/libjavajpeg/jchuff.c:808:18: 
error: array subscript is below array bounds [-Werror=array-bounds]
      while (bits[j] == 0)
                 ^

It looks to me that this error happens because the while loop can 
technically 
reduce j down to beneath 0, resulting in us attempting to find the array 
entry 
with index -1.

On the basis that if we get down to -1 here bad things will happen 
regardless,
perhaps we should change that line to:

      while ((bits[j] == 0) && (j != 0))

This appears to prevent the compiler failing with this error, by providing 

unambiguous handling for the "index -1" scenario.

Thoughts?

Best Regards

Adam Farley

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