[x264-devel] [PATCH] Fix float-cast-overflow in x264_ratecontrol_end function.

[BugMaster]

On Mon, 25 Jan 2016 16:05:25 -0800, Alexey Samsonov wrote:
> According to C standard, it is undefined behavior to cast negative
> floating point number to unsigned integer. Float-cast-overflow in
> general is known to produce different results on different architectures.

> Building x264 code with Clang and -fsanitize=float-cast-overflow
> (http://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html#availablle-checks)
> and running it on some real-life examples occasionally produces errors
> of the form:

> encoder/ratecontrol.c:1892: runtime error: value -5011.14 is
> outside the range of representable values of type 'unsigned short'

> Fix these errors by explicitly coding de-facto x86 behavior: casting
> float to uint16_t through int.
> ---
>  encoder/ratecontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

> diff --git a/encoder/ratecontrol.c b/encoder/ratecontrol.c
> index d8d06b3..a16755e 100644
> --- a/encoder/ratecontrol.c
> +++ b/encoder/ratecontrol.c
> @@ -1889,7 +1889,7 @@ int x264_ratecontrol_end( x264_t *h, int bits, int *filler )
>              uint8_t i_type = h->sh.i_type;
>              /* Values are stored as big-endian FIX8.8 */
>              for( int i = 0; i < h->mb.i_mb_count; i++ )
> -                rc->mbtree.qp_buffer[0][i] = endian_fix16( h->fenc->f_qp_offset[i]*256.0 );
> +                rc->mbtree.qp_buffer[0][i] = endian_fix16(
> (int)(h->fenc->f_qp_offset[i]*256.0) );
>              if( fwrite( &i_type, 1, 1, rc->p_mbtree_stat_file_out ) < 1 )
>                  goto fail;
>              if( fwrite( rc->mbtree.qp_buffer[0], sizeof(uint16_t),
> h->mb.i_mb_count, rc->p_mbtree_stat_file_out ) < h->mb.i_mb_count )

Hi. Thanks for the patch. In general I am agree with this change but
imho it should be cast to int16_t and not to int. int16_t should
better explain the limits we expect in this cast (if for some reason
this cast will be with saturation).