On 1/21/2019 4:09 PM, FeRD (Frank Dana) wrote:
> The RSHIFT macro in libavutil/common.h does not actually perform
> a bitwise right-shift, but rather a rounded version of the same
> operation, as is noted by a comment above the macro. The rounded
> divsion macro on the very next line is named ROUNDED_DIV, which
> seems far more clear.
>
> This patch renames RSHIFT to ROUNDED_RSHIFT, then updates all
> uses of the macro to use the new name. (These are all located
> in three codec files under libavcodec/.)
>
> Signed-off-by: FeRD (Frank Dana) <ferd...@gmail.com>
> ---
> libavcodec/mpeg4videodec.c | 4 ++--
> libavcodec/vp3.c | 16 ++++++++--------
> libavcodec/vp56.c | 4 ++--
> libavutil/common.h | 2 +-
> 4 files changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
> index f44ee76bd4..5d63ba12ba 100644
> --- a/libavcodec/mpeg4videodec.c
> +++ b/libavcodec/mpeg4videodec.c
> @@ -601,7 +601,7 @@ static inline int get_amv(Mpeg4DecContext *ctx, int n)
> if (ctx->divx_version == 500 && ctx->divx_build == 413 && a >=
> s->quarter_sample)
> sum = s->sprite_offset[0][n] / (1 << (a - s->quarter_sample));
> else
> - sum = RSHIFT(s->sprite_offset[0][n] * (1 << s->quarter_sample),
> a);
> + sum = ROUNDED_RSHIFT(s->sprite_offset[0][n] * (1 <<
> s->quarter_sample), a);
> } else {
> dx = s->sprite_delta[n][0];
> dy = s->sprite_delta[n][1];
> @@ -623,7 +623,7 @@ static inline int get_amv(Mpeg4DecContext *ctx, int n)
> v += dx;
> }
> }
> - sum = RSHIFT(sum, a + 8 - s->quarter_sample);
> + sum = ROUNDED_RSHIFT(sum, a + 8 - s->quarter_sample);
> }
>
> if (sum < -len)
> diff --git a/libavcodec/vp3.c b/libavcodec/vp3.c
> index a5d8c2ed0b..13b3d6e22a 100644
> --- a/libavcodec/vp3.c
> +++ b/libavcodec/vp3.c
> @@ -861,10 +861,10 @@ static int unpack_vectors(Vp3DecodeContext *s,
> GetBitContext *gb)
>
> if (s->chroma_y_shift) {
> if (s->macroblock_coding[current_macroblock] ==
> MODE_INTER_FOURMV) {
> - motion_x[0] = RSHIFT(motion_x[0] + motion_x[1] +
> - motion_x[2] + motion_x[3], 2);
> - motion_y[0] = RSHIFT(motion_y[0] + motion_y[1] +
> - motion_y[2] + motion_y[3], 2);
> + motion_x[0] = ROUNDED_RSHIFT(motion_x[0] +
> motion_x[1] +
> + motion_x[2] +
> motion_x[3], 2);
> + motion_y[0] = ROUNDED_RSHIFT(motion_y[0] +
> motion_y[1] +
> + motion_y[2] +
> motion_y[3], 2);
> }
> motion_x[0] = (motion_x[0] >> 1) | (motion_x[0] & 1);
> motion_y[0] = (motion_y[0] >> 1) | (motion_y[0] & 1);
> @@ -873,10 +873,10 @@ static int unpack_vectors(Vp3DecodeContext *s,
> GetBitContext *gb)
> s->motion_val[1][frag][1] = motion_y[0];
> } else if (s->chroma_x_shift) {
> if (s->macroblock_coding[current_macroblock] ==
> MODE_INTER_FOURMV) {
> - motion_x[0] = RSHIFT(motion_x[0] + motion_x[1], 1);
> - motion_y[0] = RSHIFT(motion_y[0] + motion_y[1], 1);
> - motion_x[1] = RSHIFT(motion_x[2] + motion_x[3], 1);
> - motion_y[1] = RSHIFT(motion_y[2] + motion_y[3], 1);
> + motion_x[0] = ROUNDED_RSHIFT(motion_x[0] +
> motion_x[1], 1);
> + motion_y[0] = ROUNDED_RSHIFT(motion_y[0] +
> motion_y[1], 1);
> + motion_x[1] = ROUNDED_RSHIFT(motion_x[2] +
> motion_x[3], 1);
> + motion_y[1] = ROUNDED_RSHIFT(motion_y[2] +
> motion_y[3], 1);
> } else {
> motion_x[1] = motion_x[0];
> motion_y[1] = motion_y[0];
> diff --git a/libavcodec/vp56.c b/libavcodec/vp56.c
> index b69fe6c176..9359b48bc6 100644
> --- a/libavcodec/vp56.c
> +++ b/libavcodec/vp56.c
> @@ -197,8 +197,8 @@ static void vp56_decode_4mv(VP56Context *s, int row, int
> col)
>
> /* chroma vectors are average luma vectors */
> if (s->avctx->codec->id == AV_CODEC_ID_VP5) {
> - s->mv[4].x = s->mv[5].x = RSHIFT(mv.x,2);
> - s->mv[4].y = s->mv[5].y = RSHIFT(mv.y,2);
> + s->mv[4].x = s->mv[5].x = ROUNDED_RSHIFT(mv.x,2);
> + s->mv[4].y = s->mv[5].y = ROUNDED_RSHIFT(mv.y,2);
> } else {
> s->mv[4] = s->mv[5] = (VP56mv) {mv.x/4, mv.y/4};
> }
> diff --git a/libavutil/common.h b/libavutil/common.h
> index 8db0291170..0bff7f8f72 100644
> --- a/libavutil/common.h
> +++ b/libavutil/common.h
> @@ -51,7 +51,7 @@
> #endif
>
> //rounded division & shift
> -#define RSHIFT(a,b) ((a) > 0 ? ((a) + ((1<<(b))>>1))>>(b) : ((a) +
> ((1<<(b))>>1)-1)>>(b))
> +#define ROUNDED_RSHIFT(a,b) ((a) > 0 ? ((a) + ((1<<(b))>>1))>>(b) : ((a) +
> ((1<<(b))>>1)-1)>>(b))
common.h is a public installed library, so this would be an API break.
There's also no good way to deprecate a define and replace it with
another while informing the library user, so for something purely
cosmetic like this i don't think it's worth the trouble.
> /* assume b>0 */
> #define ROUNDED_DIV(a,b) (((a)>0 ? (a) + ((b)>>1) : (a) - ((b)>>1))/(b))
> /* Fast a/(1<<b) rounded toward +inf. Assume a>=0 and b>=0 */
>
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