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Add and use SDL_FALLTHROUGH for fallthroughs

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Case fallthrough warnings can be suppressed using the __fallthrough__
compiler attribute. Unfortunately, not all compilers have this
attribute, or even have __has_attribute to check if they have the
__fallthrough__ attribute. [[fallthrough]] is also available in C++17
and the next C2x, but not everyone uses C++17 or C2x.

So define the SDL_FALLTHROUGH macro to deal with those problems - if we
are using C++17 or C2x, it expands to [[fallthrough]]; else if the
compiler has __has_attribute and has the __fallthrough__ attribute, then
it expands to __attribute__((__fallthrough__)); else it expands to an
empty statement, with a /* fallthrough */ comment (it's a do {} while
(0) statement, because users of this macro need to use a semicolon,
because [[fallthrough]] and __attribute__((__fallthrough__)) require a
semicolon).

Applications using SDL are also free to use this macro (because it is
defined in begin_code.h).

All existing /* fallthrough */ comments have been replaced with this
macro. Some of them were unnecessary because they were the last case in
a switch; using SDL_FALLTHROUGH in those cases would result in a compile
error on compilers that support __fallthrough__, for having a
__attribute__((__fallthrough__)) statement that didn't immediately
precede a case label.
This commit is contained in:
Misa
2021-09-27 14:38:12 -07:00
committed by Sam Lantinga
parent 828a0a4a10
commit 66a08aa391
15 changed files with 63 additions and 55 deletions
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24
src/video/SDL_blit.h
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@@ -479,14 +479,14 @@ do { \
#define DUFFS_LOOP8(pixel_copy_increment, width) \
{ int n = (width+7)/8; \
switch (width & 7) { \
case 0: do { pixel_copy_increment; /* fallthrough */ \
case 7: pixel_copy_increment; /* fallthrough */ \
case 6: pixel_copy_increment; /* fallthrough */ \
case 5: pixel_copy_increment; /* fallthrough */ \
case 4: pixel_copy_increment; /* fallthrough */ \
case 3: pixel_copy_increment; /* fallthrough */ \
case 2: pixel_copy_increment; /* fallthrough */ \
case 1: pixel_copy_increment; /* fallthrough */ \
case 0: do { pixel_copy_increment; SDL_FALLTHROUGH; \
case 7: pixel_copy_increment; SDL_FALLTHROUGH; \
case 6: pixel_copy_increment; SDL_FALLTHROUGH; \
case 5: pixel_copy_increment; SDL_FALLTHROUGH; \
case 4: pixel_copy_increment; SDL_FALLTHROUGH; \
case 3: pixel_copy_increment; SDL_FALLTHROUGH; \
case 2: pixel_copy_increment; SDL_FALLTHROUGH; \
case 1: pixel_copy_increment; \
} while ( --n > 0 ); \
} \
}
@@ -495,10 +495,10 @@ do { \
#define DUFFS_LOOP4(pixel_copy_increment, width) \
{ int n = (width+3)/4; \
switch (width & 3) { \
case 0: do { pixel_copy_increment; /* fallthrough */ \
case 3: pixel_copy_increment; /* fallthrough */ \
case 2: pixel_copy_increment; /* fallthrough */ \
case 1: pixel_copy_increment; /* fallthrough */ \
case 0: do { pixel_copy_increment; SDL_FALLTHROUGH; \
case 3: pixel_copy_increment; SDL_FALLTHROUGH; \
case 2: pixel_copy_increment; SDL_FALLTHROUGH; \
case 1: pixel_copy_increment; \
} while (--n > 0); \
} \
}