Re: [FFmpeg-devel] [PATCH 2/2] swscale/output: Bias 16bps output calculations to improve non overflowing range for GBRP16/GBRPF32

[Mark Reid <mindmark@gmail.com>]

On Wed, Nov 2, 2022 at 3:52 PM Mark Reid <mindmark@gmail.com> wrote:

>
>
> On Wed, Nov 2, 2022 at 2:03 PM Michael Niedermayer <michael@niedermayer.cc>
> wrote:
>
>> Fixes: integer overflow
>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>> ---
>>  libswscale/output.c       | 25 +++++++++++--------------
>>  libswscale/x86/output.asm | 16 +++++++++++++++-
>>  2 files changed, 26 insertions(+), 15 deletions(-)
>>
>> diff --git a/libswscale/output.c b/libswscale/output.c
>> index df4647adde..5c85bff971 100644
>> --- a/libswscale/output.c
>> +++ b/libswscale/output.c
>> @@ -2372,18 +2372,15 @@ yuv2gbrp16_full_X_c(SwsContext *c, const int16_t
>> *lumFilter,
>>
>>          Y -= c->yuv2rgb_y_offset;
>>          Y *= c->yuv2rgb_y_coeff;
>> -        Y += 1 << 13;
>> +        Y += (1 << 13) - (1 << 29);
>>          R = V * c->yuv2rgb_v2r_coeff;
>>          G = V * c->yuv2rgb_v2g_coeff + U * c->yuv2rgb_u2g_coeff;
>>          B =                            U * c->yuv2rgb_u2b_coeff;
>>
>> -        R = av_clip_uintp2(Y + R, 30);
>> -        G = av_clip_uintp2(Y + G, 30);
>> -        B = av_clip_uintp2(Y + B, 30);
>> +        dest16[2][i] = av_clip_uintp2(((Y + R) >> 14) + (1<<15), 16);
>> +        dest16[0][i] = av_clip_uintp2(((Y + G) >> 14) + (1<<15), 16);
>> +        dest16[1][i] = av_clip_uintp2(((Y + B) >> 14) + (1<<15), 16);
>>
>> -        dest16[0][i] = G >> 14;
>> -        dest16[1][i] = B >> 14;
>> -        dest16[2][i] = R >> 14;
>>          if (hasAlpha)
>>              dest16[3][i] = av_clip_uintp2(A, 30) >> 14;
>>      }
>> @@ -2448,18 +2445,18 @@ yuv2gbrpf32_full_X_c(SwsContext *c, const int16_t
>> *lumFilter,
>>
>>          Y -= c->yuv2rgb_y_offset;
>>          Y *= c->yuv2rgb_y_coeff;
>> -        Y += 1 << 13;
>> +        Y += (1 << 13) - (1 << 29);
>>          R = V * c->yuv2rgb_v2r_coeff;
>>          G = V * c->yuv2rgb_v2g_coeff + U * c->yuv2rgb_u2g_coeff;
>>          B =                            U * c->yuv2rgb_u2b_coeff;
>>
>> -        R = av_clip_uintp2(Y + R, 30);
>> -        G = av_clip_uintp2(Y + G, 30);
>> -        B = av_clip_uintp2(Y + B, 30);
>> +        R = av_clip_uintp2(((Y + R) >> 14) + (1<<15), 16);
>> +        G = av_clip_uintp2(((Y + G) >> 14) + (1<<15), 16);
>> +        B = av_clip_uintp2(((Y + B) >> 14) + (1<<15), 16);
>>
>> -        dest32[0][i] = av_float2int(float_mult * (float)(G >> 14));
>> -        dest32[1][i] = av_float2int(float_mult * (float)(B >> 14));
>> -        dest32[2][i] = av_float2int(float_mult * (float)(R >> 14));
>> +        dest32[0][i] = av_float2int(float_mult * (float)G);
>> +        dest32[1][i] = av_float2int(float_mult * (float)B);
>> +        dest32[2][i] = av_float2int(float_mult * (float)R);
>>          if (hasAlpha)
>>              dest32[3][i] = av_float2int(float_mult *
>> (float)(av_clip_uintp2(A, 30) >> 14));
>>      }
>> diff --git a/libswscale/x86/output.asm b/libswscale/x86/output.asm
>> index 84e94baaf6..f943a27534 100644
>> --- a/libswscale/x86/output.asm
>> +++ b/libswscale/x86/output.asm
>> @@ -44,11 +44,13 @@ pd_yuv2gbrp_y_start:       times 8 dd  (1 << 9)
>>  pd_yuv2gbrp_uv_start:      times 8 dd  ((1 << 9) - (128 << 19))
>>  pd_yuv2gbrp_a_start:       times 8 dd  (1 << 18)
>>  pd_yuv2gbrp16_offset:      times 8 dd  0x10000  ;(1 << 16)
>> -pd_yuv2gbrp16_round13:     times 8 dd  0x02000  ;(1 << 13)
>> +pd_yuv2gbrp16_round13:     times 8 dd  0xE0002000  ;(1 << 13) - (1 << 29)
>>  pd_yuv2gbrp16_a_offset:    times 8 dd  0x20002000
>>  pd_yuv2gbrp16_upper30:     times 8 dd  0x3FFFFFFF ;(1<<30) - 1
>>  pd_yuv2gbrp16_upper27:     times 8 dd  0x07FFFFFF ;(1<<27) - 1
>> +pd_yuv2gbrp16_upper16:     times 8 dd  0x0000FFFF ;(1<<16) - 1
>>
>
> pd_yuv2gbrp16_upper16 doesn't appear to be used anywhere
>

nevermind, I see where it is used now.


>
>
>>  pd_yuv2gbrp16_upperC:      times 8 dd  0xC0000000
>> +pd_yuv2gbrp_debias:        times 8 dd  0x00008000 ;(1 << 29 - 14)
>>  pb_pack_shuffle8:       db  0,  4,  8, 12, \
>>                             -1, -1, -1, -1, \
>>                             -1, -1, -1, -1, \
>> @@ -883,14 +885,26 @@ cglobal yuv2%1_full_X, 12, 14, 16, ptr, lumFilter,
>> lumSrcx, lumFilterSize, chrFi
>>          paddd G, Y
>>          paddd B, Y
>>
>> +%if  DEPTH < 16
>>          CLIPP2 R, 30
>>          CLIPP2 G, 30
>>          CLIPP2 B, 30
>> +%endif
>>
>>          psrad R, RGB_SHIFT
>>          psrad G, RGB_SHIFT
>>          psrad B, RGB_SHIFT
>>
>> +%if  DEPTH >= 16
>> +        paddd R, [pd_yuv2gbrp_debias]
>> +        paddd G, [pd_yuv2gbrp_debias]
>> +        paddd B, [pd_yuv2gbrp_debias]
>> +
>> +        CLIPP2 R, 16
>> +        CLIPP2 G, 16
>> +        CLIPP2 B, 16
>> +%endif
>> +
>>  %if FLOAT
>>          cvtdq2ps R, R
>>          cvtdq2ps G, G
>> --
>> 2.17.1
>>
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