New Ghostscript/GhostPDL compiler warnings - 2017-11-20-07:45:03 - 1b64014143a8a571e5dbff3346c6ad902603dda1

Previous Revision: cea5d8a72dab953fe84ab8f7280003d377559fff
 Current Revision: 1b64014143a8a571e5dbff3346c6ad902603dda1

commit 1b64014143a8a571e5dbff3346c6ad902603dda1
Author:     Robin Watts <[email protected]>
AuthorDate: Mon Nov 20 14:33:03 2017 +0000
CommitDate: Mon Nov 20 14:38:01 2017 +0000

    Fix release/debug difference.
    
    In searching for the indeterminism in 11-14.PS, I found that I could
    run the same command line in release and debug builds on peeved, and
    get different results:
    
     touch out1.pgm ref1.pgm && rm out*.pgm ref*.pgm &&
     bin/gs -sOutputFile=ref%d.pgm -dMaxBitmap=10000 -sDEVICE=pgmraw -r300
     -Z: -sDEFAULTPAPERSIZE=letter -dNOPAUSE -dBATCH -K2000000 -dClusterJob
     -dJOBSERVER %rom%Resource/Init/gs_cet.ps cutdown >& ~/log &&
     debugbin/gs -sOutputFile=out%d.pgm -dMaxBitmap=10000 -sDEVICE=pgmraw
     -r300 -Z: -sDEFAULTPAPERSIZE=letter -dNOPAUSE -dBATCH -K2000000
     -dClusterJob -dJOBSERVER %rom%Resource/Init/gs_cet.ps cutdown
     >& ~/log2 && md5sum ref*.pgm out*.pgm && less ~/log ~/log2
    
    After cutting down the file as much as I could, Chris reduced it
    simply to:
    
     3E9 3E9 moveto 1 1 lineto stroke showpage
    
    Thanks for this!
    
    Tracing through the code, I discovered that the difference came down
    to check_diff_overflow, where the release build was assuming that if
    v1 > v0, v0 - v1 < 0, which is acceptable because v0 - v1 has
    overflown, at which point C says the value is unpredictable.
    
    The fix is to detect the overflow before it happens.

base/gxpflat.c



Ghostscript:

new clang warnings (clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)): 

./base/gxpflat.c:274:22: warning: shifting a negative signed value is undefined [-Wshift-negative-value]
        return (v0 < min_fixed + v1);
                     ^~~~~~~~~
./base/gxfixed.h:32:20: note: expanded from macro 'min_fixed'
# define min_fixed min_int
                   ^~~~~~~
./base/std.h:65:21: note: expanded from macro 'min_int'
#define min_int (-1 << (ARCH_SIZEOF_INT * 8 - 1))
                 ~~ ^

./base/gxpflat.c:276:22: warning: shifting a negative signed value is undefined [-Wshift-negative-value]
        return (v0 > max_fixed + v1);
                     ^~~~~~~~~
./base/gxfixed.h:31:20: note: expanded from macro 'max_fixed'
# define max_fixed max_int
                   ^~~~~~~
./base/std.h:66:19: note: expanded from macro 'max_int'
#define max_int (~min_int)
                  ^~~~~~~
./base/std.h:65:21: note: expanded from macro 'min_int'
#define min_int (-1 << (ARCH_SIZEOF_INT * 8 - 1))
                 ~~ ^


http://miles.ghostscript.com:8080/artifex/1b64014143a8a571e5dbff3346c6ad902603dda1/gs-clang-warnings.txt