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On 05/19/2011 08:14 PM, Adam Jackson wrote:
> Despite that negative values aren't sensible here, making this unsigned
> is dangerous. Consider get_pointer_generic, which computes a value of
> the form:
>
> void *base + (int x * int stride + int y) * unsigned bpp
>
> The usual arithmetic conversions will coerce the (x*stride + y)
> subexpression to unsigned. Since stride can be negative, this is
> disastrous.
>
> Fixes at least the following piglit tests on Ironlake:
>
> fbo/fbo-blit-d24s8
> spec/ARB_depth_texture/fbo-clear-formats
> spec/EXT_packed_depth_stencil/fbo-clear-formats
>
> Signed-off-by: Adam Jackson <a...@redhat.com>
I don't care which approach we go with. This will likely fix it
everywhere, but I'd like there to be a comment explaining why the return
type must not be unsigned. Otherwise someone will come along in the
future and make it unsigned in the name of "code cleanup."
> ---
> src/mesa/main/formats.c | 2 +-
> src/mesa/main/formats.h | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/mesa/main/formats.c b/src/mesa/main/formats.c
> index 60e8ae3..a46633b 100644
> --- a/src/mesa/main/formats.c
> +++ b/src/mesa/main/formats.c
> @@ -1119,7 +1119,7 @@ _mesa_get_format_name(gl_format format)
> * Normally, a block is 1x1 (a single pixel). But for compressed formats
> * a block may be 4x4 or 8x4, etc.
> */
> -GLuint
> +GLint
> _mesa_get_format_bytes(gl_format format)
> {
> const struct gl_format_info *info = _mesa_get_format_info(format);
> diff --git a/src/mesa/main/formats.h b/src/mesa/main/formats.h
> index df9ed70..0640bbc 100644
> --- a/src/mesa/main/formats.h
> +++ b/src/mesa/main/formats.h
> @@ -216,7 +216,7 @@ typedef enum
> extern const char *
> _mesa_get_format_name(gl_format format);
>
> -extern GLuint
> +extern GLint
> _mesa_get_format_bytes(gl_format format);
>
> extern GLint
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