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[smooth] Fix left shifts of negative numbers. 

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=36241

* src/smooth/ftgrays.c (LEFT_SHIFT): New macro.
(gray_render_conic) [BEZIER_USE_DDA]: Use it.
This commit is contained in:
Werner Lemberg 2021-08-06 08:31:22 +02:00
parent 09195a82a4
commit 6be8bfe499
1 changed files with 16 additions and 11 deletions
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27
src/smooth/ftgrays.c
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@ -1035,6 +1035,9 @@ typedef ptrdiff_t FT_PtrDist;
# include <emmintrin.h>
#endif
#define LEFT_SHIFT( a, b ) (FT_Int64)( (FT_UInt64)(a) << (b) )
static void
gray_render_conic( RAS_ARG_ const FT_Vector* control,
const FT_Vector* to )
@ -1126,13 +1129,15 @@ typedef ptrdiff_t FT_PtrDist;
* EMIT(P)
*
* To ensure accurate results, perform computations on 64-bit
* values, after scaling them by 2^32:
* values, after scaling them by 2^32.
*
* R << 32 = 2 * A << (32 - N - N)
* = A << (33 - 2 *N)
* h = 1 / 2^N
*
* Q << 32 = (2 * B << (32 - N)) + (A << (32 - N - N))
* = (B << (33 - N)) + (A << (32 - N - N))
* R << 32 = 2 * A << (32 - N - N)
* = A << (33 - 2*N)
*
* Q << 32 = (2 * B << (32 - N)) + (A << (32 - N - N))
* = (B << (33 - N)) + (A << (32 - 2*N))
*/
#ifdef __SSE2__
@ -1199,14 +1204,14 @@ typedef ptrdiff_t FT_PtrDist;
bx = p1.x - p0.x;
by = p1.y - p0.y;
rx = ax << ( 33 - 2 * shift );
ry = ay << ( 33 - 2 * shift );
rx = LEFT_SHIFT( ax, 33 - 2 * shift );
ry = LEFT_SHIFT( ay, 33 - 2 * shift );
qx = ( bx << ( 33 - shift ) ) + ( ax << ( 32 - 2 * shift ) );
qy = ( by << ( 33 - shift ) ) + ( ay << ( 32 - 2 * shift ) );
qx = LEFT_SHIFT( bx, 33 - shift ) + LEFT_SHIFT( ax, 32 - 2 * shift );
qy = LEFT_SHIFT( by, 33 - shift ) + LEFT_SHIFT( ay, 32 - 2 * shift );
px = (FT_Int64)p0.x << 32;
py = (FT_Int64)p0.y << 32;
px = LEFT_SHIFT( p0.x, 32 );
py = LEFT_SHIFT( p0.y, 32 );
for ( count = 1U << shift; count > 0; count-- )
{