Fix up signed-integer-overflow warnings

When checking whether a matrix was a pure scale, we subtracted
0x3f800000 from the diagonals; if the diagonal value was already
very negative, we'd underflow. Replace subtraction with XOR.

When dealing with repeating tiled bitmaps, when the bitmap was
very large, we'd multiply an offset by 65535, possibly causing
underflow. Throw in a cast to long (casting to unsigned also
silences the warning and wouldn't involve extension, but I can't
convince myself that it's correct).

BUG=skia:4635
R=mtklein@google.com

Review URL: https://codereview.chromium.org/1504933002

1 files changed, 8 insertions, 6 deletions

diff --git a/src/core/SkBitmapProcState_matrixProcs.cpp b/src/core/SkBitmapProcState_matrixProcs.cpp
index 1870a0e50e..ee61ee8556 100644
--- a/src/core/SkBitmapProcState_matrixProcs.cpp
+++ b/src/core/SkBitmapProcState_matrixProcs.cpp
@@ -95,18 +95,20 @@ static SkBitmapProcState::MatrixProc ClampX_ClampY_Procs[] = {
 };
 
 #define MAKENAME(suffix)        RepeatX_RepeatY ## suffix
-#define TILEX_PROCF(fx, max)    SK_USHIFT16(((fx) & 0xFFFF) * ((max) + 1))
-#define TILEY_PROCF(fy, max)    SK_USHIFT16(((fy) & 0xFFFF) * ((max) + 1))
-#define TILEX_LOW_BITS(fx, max) ((((fx) & 0xFFFF) * ((max) + 1) >> 12) & 0xF)
-#define TILEY_LOW_BITS(fy, max) ((((fy) & 0xFFFF) * ((max) + 1) >> 12) & 0xF)
+#define TILEX_PROCF(fx, max)    SK_USHIFT16((unsigned)((fx) & 0xFFFF) * ((max) + 1))
+#define TILEY_PROCF(fy, max)    SK_USHIFT16((unsigned)((fy) & 0xFFFF) * ((max) + 1))
+#define TILEX_LOW_BITS(fx, max) (((unsigned)((fx) & 0xFFFF) * ((max) + 1) >> 12) & 0xF)
+#define TILEY_LOW_BITS(fy, max) (((unsigned)((fy) & 0xFFFF) * ((max) + 1) >> 12) & 0xF)
 #include "SkBitmapProcState_matrix.h"
 
 struct RepeatTileProcs {
     static unsigned X(const SkBitmapProcState&, SkFixed fx, int max) {
-        return SK_USHIFT16(((fx) & 0xFFFF) * ((max) + 1));
+        SkASSERT(max < 65535);
+        return SK_USHIFT16((unsigned)((fx) & 0xFFFF) * ((max) + 1));
     }
     static unsigned Y(const SkBitmapProcState&, SkFixed fy, int max) {
-        return SK_USHIFT16(((fy) & 0xFFFF) * ((max) + 1));
+        SkASSERT(max < 65535);
+        return SK_USHIFT16((unsigned)((fy) & 0xFFFF) * ((max) + 1));
     }
 };