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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.
This commit is contained in:
James Legg 2020-05-29 13:05:37 +01:00
parent 032fa681a8
commit e2dbed9cfe
1 changed files with 5 additions and 5 deletions
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10
src/video/SDL_blit_N.c
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@ -2183,7 +2183,7 @@ Blit4to4MaskAlpha(SDL_BlitInfo * info)
if (dstfmt->Amask) { if (dstfmt->Amask) {
/* RGB->RGBA, SET_ALPHA */ /* RGB->RGBA, SET_ALPHA */
Uint32 mask = (info->a >> dstfmt->Aloss) << dstfmt->Ashift; Uint32 mask = ((Uint32)info->a >> dstfmt->Aloss) << dstfmt->Ashift;
while (height--) { while (height--) {
/* *INDENT-OFF* */ /* *INDENT-OFF* */
@ -2632,7 +2632,7 @@ BlitNtoNKey(SDL_BlitInfo * info)
if (dstfmt->Amask) { if (dstfmt->Amask) {
/* RGB->RGBA, SET_ALPHA */ /* RGB->RGBA, SET_ALPHA */
Uint32 mask = info->a << dstfmt->Ashift; Uint32 mask = ((Uint32)info->a) << dstfmt->Ashift;
while (height--) { while (height--) {
/* *INDENT-OFF* */ /* *INDENT-OFF* */
DUFFS_LOOP( DUFFS_LOOP(
@ -3059,7 +3059,7 @@ Blit_3or4_to_3or4__same_rgb(SDL_BlitInfo * info)
if (dstfmt->Amask) { if (dstfmt->Amask) {
/* SET_ALPHA */ /* SET_ALPHA */
Uint32 mask = info->a << dstfmt->Ashift; Uint32 mask = ((Uint32)info->a) << dstfmt->Ashift;
#if SDL_BYTEORDER == SDL_LIL_ENDIAN #if SDL_BYTEORDER == SDL_LIL_ENDIAN
int i0 = 0, i1 = 1, i2 = 2; int i0 = 0, i1 = 1, i2 = 2;
#else #else
@ -3148,7 +3148,7 @@ Blit_3or4_to_3or4__inversed_rgb(SDL_BlitInfo * info)
Uint8 s0 = src[i0]; Uint8 s0 = src[i0];
Uint8 s1 = src[i1]; Uint8 s1 = src[i1];
Uint8 s2 = src[i2]; 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 */ /* inversed, compared to Blit_3or4_to_3or4__same_rgb */
*dst32 = (s0 << 16) | (s1 << 8) | (s2) | alphashift; *dst32 = (s0 << 16) | (s1 << 8) | (s2) | alphashift;
dst += 4; dst += 4;
@ -3160,7 +3160,7 @@ Blit_3or4_to_3or4__inversed_rgb(SDL_BlitInfo * info)
} }
} else { } else {
/* SET_ALPHA */ /* SET_ALPHA */
Uint32 mask = info->a << dstfmt->Ashift; Uint32 mask = ((Uint32)info->a) << dstfmt->Ashift;
#if SDL_BYTEORDER == SDL_LIL_ENDIAN #if SDL_BYTEORDER == SDL_LIL_ENDIAN
int i0 = 0, i1 = 1, i2 = 2; int i0 = 0, i1 = 1, i2 = 2;
#else #else