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Remove default-zero for `physfsrwops_seek` variable pos 

This default-zero allowed the bug introduced in
68b47307b4 (and fixed in
4c371734b5) not to generate a compiler
warning for `-Wuninitialized`, since it was initialized to `0`.
However, `0` is not a correct starting value for this variable.  Remove
the initialization and require every code path to assign a meaningful
value.

Switch to use `std::in_range` to validate that no truncation occurs, and
trust that the compiler will optimize this out when the type passed to
`std::in_range` can represent all values that the argument can
represent.
This commit is contained in:
Kp 2023-05-27 13:19:31 +00:00
parent 695e8b9ba1
commit 03cedbb4cc
1 changed files with 27 additions and 17 deletions
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44
common/misc/physfsrwops.cpp
View File

@ -45,7 +45,7 @@ namespace {
static SDL_RWops_callback_seek_position physfsrwops_seek(SDL_RWops *rw, const SDL_RWops_callback_seek_position offset, const int whence)
{
PHYSFS_File *handle = reinterpret_cast<PHYSFS_File *>(rw->hidden.unknown.data1);
SDL_RWops_callback_seek_position pos = 0;
SDL_RWops_callback_seek_position pos;
if (whence == SEEK_SET)
{
@ -62,21 +62,35 @@ static SDL_RWops_callback_seek_position physfsrwops_seek(SDL_RWops *rw, const SD
return(-1);
} /* if */
#if SDL_MAJOR_VERSION == 1
pos = static_cast<int>(current);
if (static_cast<PHYSFS_sint64>(pos) != current)
if (!std::in_range<SDL_RWops_callback_seek_position>(current))
{
SDL_SetError("Can't fit current file position in an int!");
return(-1);
} /* if */
#else
pos = current;
#endif
if (offset == 0) /* this is a "tell" call. We're done. */
return(pos);
return current;
pos += offset;
/* When `SDL_RWops_callback_seek_position` is `int`, this assignment
* converts to a narrower type, but the call to std::in_range above
* rejected any values for which the narrowing would change the
* observed value. An assignment which prohibits narrowing would be
* ill-formed, since the compile-time check for narrowing is
* context-free and assumes the worst case. Therefore, an
* initialization that prohibited narrowing would trigger a compile
* error.
*
* When `SDL_RWops_callback_seek_position` is `Sint64`, then on
* x86_64-w64-mingw32,
* `static_cast<SDL_RWops_callback_seek_position>(v)` triggers
* `-Wuseless-cast`.
*
* When `SDL_RWops_callback_seek_position` is `Sint64`, then on
* x86_64-pc-linux-gnu,
* `static_cast<SDL_RWops_callback_seek_position>(v)` is accepted
* without issue.
*/
const SDL_RWops_callback_seek_position rwcurrent = current;
pos = rwcurrent + offset;
} /* else if */
else if (whence == SEEK_END)
@ -88,18 +102,14 @@ static SDL_RWops_callback_seek_position physfsrwops_seek(SDL_RWops *rw, const SD
return(-1);
} /* if */
#if SDL_MAJOR_VERSION == 1
pos = static_cast<int>(len);
if (static_cast<PHYSFS_sint64>(pos) != len)
if (!std::in_range<SDL_RWops_callback_seek_position>(len))
{
SDL_SetError("Can't fit end-of-file position in an int!");
return(-1);
} /* if */
#else
pos = len;
#endif
pos += offset;
const SDL_RWops_callback_seek_position rwlen = len;
pos = rwlen + offset;
} /* else if */
else