Commit e2dbed9cfe37bf775c705d105f5c47fa6c8ef425
2020-05-29T13:05:37
SDL_blit: Fix undefined bitshift operations Arithmatic operations promote Uint8 to signed int. If the top bit of a Uint8 is set, and it is left shifted 24 places, then the result is not representable in a signed 32 bit int. This would be undefined behaviour on systems where int is 32 bits.
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diff --git a/src/video/SDL_blit_N.c b/src/video/SDL_blit_N.c
index 39c08f6..3722f23 100644
--- a/src/video/SDL_blit_N.c
+++ b/src/video/SDL_blit_N.c
@@ -2183,7 +2183,7 @@ Blit4to4MaskAlpha(SDL_BlitInfo * info)
if (dstfmt->Amask) {
/* RGB->RGBA, SET_ALPHA */
- Uint32 mask = (info->a >> dstfmt->Aloss) << dstfmt->Ashift;
+ Uint32 mask = ((Uint32)info->a >> dstfmt->Aloss) << dstfmt->Ashift;
while (height--) {
/* *INDENT-OFF* */
@@ -2632,7 +2632,7 @@ BlitNtoNKey(SDL_BlitInfo * info)
if (dstfmt->Amask) {
/* RGB->RGBA, SET_ALPHA */
- Uint32 mask = info->a << dstfmt->Ashift;
+ Uint32 mask = ((Uint32)info->a) << dstfmt->Ashift;
while (height--) {
/* *INDENT-OFF* */
DUFFS_LOOP(
@@ -3059,7 +3059,7 @@ Blit_3or4_to_3or4__same_rgb(SDL_BlitInfo * info)
if (dstfmt->Amask) {
/* SET_ALPHA */
- Uint32 mask = info->a << dstfmt->Ashift;
+ Uint32 mask = ((Uint32)info->a) << dstfmt->Ashift;
#if SDL_BYTEORDER == SDL_LIL_ENDIAN
int i0 = 0, i1 = 1, i2 = 2;
#else
@@ -3148,7 +3148,7 @@ Blit_3or4_to_3or4__inversed_rgb(SDL_BlitInfo * info)
Uint8 s0 = src[i0];
Uint8 s1 = src[i1];
Uint8 s2 = src[i2];
- Uint32 alphashift = src[i3] << dstfmt->Ashift;
+ Uint32 alphashift = ((Uint32)src[i3]) << dstfmt->Ashift;
/* inversed, compared to Blit_3or4_to_3or4__same_rgb */
*dst32 = (s0 << 16) | (s1 << 8) | (s2) | alphashift;
dst += 4;
@@ -3160,7 +3160,7 @@ Blit_3or4_to_3or4__inversed_rgb(SDL_BlitInfo * info)
}
} else {
/* SET_ALPHA */
- Uint32 mask = info->a << dstfmt->Ashift;
+ Uint32 mask = ((Uint32)info->a) << dstfmt->Ashift;
#if SDL_BYTEORDER == SDL_LIL_ENDIAN
int i0 = 0, i1 = 1, i2 = 2;
#else