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qgrayraster: fix UBs involving << with a negative LHS

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Left-shifts of negative values are undefined in C++. In particular,
they don't behave arithmetically.

Reported by UBSan:

  qgrayraster.c:510:19: runtime error: left shift of negative value -1/-42
  qgrayraster.c:537:26: runtime error: left shift of negative value -1/-4/-128
  qgrayraster.c:538:26: runtime error: left shift of negative value -1/-4/-128
  qgrayraster.c:641:28: runtime error: left shift of negative value -1/-42
  qgrayraster.c:676:44: runtime error: left shift of negative value -1/-4/-5/-14/-129
  qgrayraster.c:807:19: runtime error: left shift of negative value -1/-42
  qgrayraster.c:1101:9: runtime error: left shift of negative value -32/-46/-224/-8160
  qgrayraster.c:1102:9: runtime error: left shift of negative value -32/-2626
  qgrayraster.c:1454:36: runtime error: left shift of negative value -32/-96/-224/-466/-2626/-8160
  qgrayraster.c:1535:30: runtime error: left shift of negative value -32/-46/-224/-2626/-8160

Fix by using ordinary multiplication instead, because negative
left-hand-side values don't look like they are an error.

Change-Id: I2e96de51adb4a030de8a49869ddd98a31dab31b3
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
This commit is contained in:
Marc Mutz 2016-03-12 11:34:48 +01:00
parent f24cc53cc2
commit 8141d64527
1 changed files with 2 additions and 2 deletions
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4
src/gui/painting/qgrayraster.c
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@ -202,13 +202,13 @@
#define ONE_PIXEL ( 1L << PIXEL_BITS )
#define PIXEL_MASK ( -1L << PIXEL_BITS )
#define TRUNC( x ) ( (TCoord)( (x) >> PIXEL_BITS ) )
#define SUBPIXELS( x ) ( (TPos)(x) << PIXEL_BITS )
#define SUBPIXELS( x ) ( (TPos)(x) * ( 1 << PIXEL_BITS ) )
#define FLOOR( x ) ( (x) & -ONE_PIXEL )
#define CEILING( x ) ( ( (x) + ONE_PIXEL - 1 ) & -ONE_PIXEL )
#define ROUND( x ) ( ( (x) + ONE_PIXEL / 2 ) & -ONE_PIXEL )
#if PIXEL_BITS >= 6
#define UPSCALE( x ) ( (x) << ( PIXEL_BITS - 6 ) )
#define UPSCALE( x ) ( (x) * ( 1 << ( PIXEL_BITS - 6 ) ) )
#define DOWNSCALE( x ) ( (x) >> ( PIXEL_BITS - 6 ) )
#else
#define UPSCALE( x ) ( (x) >> ( 6 - PIXEL_BITS ) )