lavfi/gradfun: fix rounding in MMX code.

Current code divides before increasing precision.

Also reduce upper bound for strength from 255 to 64.  This will prevent
an overflow in the SSSE3 and MMX filter_line code: delta is expressed as
an u16 being shifted by 2 to the left. If it overflows, having a
strength not above 64 will make sure that m is set to 0 (making the
m*m*delta >> 14 expression void).

A value above 64 should not make any sense unless gradfun is used as
a blur filter.

Signed-off-by: Anton Khirnov <anton@khirnov.net>

diff --git a/doc/filters.texi b/doc/filters.texi
index 9b39ea50efead8cffa6cd10102621279319c7ea0..88888c60e389165c18c2a338d1c9d4e4a6fbe4f0 100644 (file)
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -1142,7 +1142,7 @@ The filter takes two optional parameters, separated by ':':
 
 @var{strength} is the maximum amount by which the filter will change
 any one pixel. Also the threshold for detecting nearly flat
-regions. Acceptable values range from .51 to 255, default value is
+regions. Acceptable values range from .51 to 64, default value is
 1.2, out-of-range values will be clipped to the valid range.
 
 @var{radius} is the neighborhood to fit the gradient to. A larger

diff --git a/libavfilter/vf_gradfun.c b/libavfilter/vf_gradfun.c
index 80b7e412e31ecb467978752ab63ed60da0ac975c..900ef604e8df5d4057ceaac2a6d672b40803e30f 100644 (file)
--- a/libavfilter/vf_gradfun.c
+++ b/libavfilter/vf_gradfun.c
@@ -128,7 +128,7 @@ static av_cold int init(AVFilterContext *ctx, const char *args)
     if (args)
         sscanf(args, "%f:%d", &thresh, &radius);
 
-    thresh = av_clipf(thresh, 0.51, 255);
+    thresh = av_clipf(thresh, 0.51, 64);
     gf->thresh = (1 << 15) / thresh;
     gf->radius = av_clip((radius + 1) & ~1, 4, 32);
 

diff --git a/libavfilter/x86/vf_gradfun.c b/libavfilter/x86/vf_gradfun.c
index b4ca86c617137022f3fa906ed7f5d8a40c73ebba..75c117a9a206a8966f1bcb6a4d1492a16dfdffd5 100644 (file)
--- a/libavfilter/x86/vf_gradfun.c
+++ b/libavfilter/x86/vf_gradfun.c
@@ -62,8 +62,8 @@ static void gradfun_filter_line_mmxext(uint8_t *dst, uint8_t *src, uint16_t *dc,
         "pminsw     %%mm7, %%mm2 \n" // m = -max(0, 127-m)
         "pmullw     %%mm2, %%mm2 \n"
         "paddw      %%mm4, %%mm0 \n" // pix += dither
-        "pmulhw     %%mm2, %%mm1 \n"
         "psllw         $2, %%mm1 \n" // m = m*m*delta >> 14
+        "pmulhw     %%mm2, %%mm1 \n"
         "paddw      %%mm1, %%mm0 \n" // pix += m
         "psraw         $7, %%mm0 \n"
         "packuswb   %%mm0, %%mm0 \n"