[FFmpeg-devel] [PATCH] avutil: Rename RSHIFT macro to ROUNDED_RSHIFT

[Carl Eugen Hoyos]

2019-01-21 21:47 GMT+01:00, James Almer <jamrial at gmail.com>:
> 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) <ferdnyc at 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.

I wonder if we should change all macros that do not start with AV/FF
at the next version bump, this seems not unreasonable.

Carl Eugen