SIMD code will not have to deal with padding itself. Overwriting in that
function may have been possible but involve large overreading of the
sources. Instead, we simply make sure the width to process is always a
multiple of 16. Additionally, there must be some actual area to process
so the SIMD code can have its boundary checks after processing the first
pixels.
---
 libavfilter/vf_nlmeans.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/libavfilter/vf_nlmeans.c b/libavfilter/vf_nlmeans.c
index d222d3913e..3f0a43ee72 100644
--- a/libavfilter/vf_nlmeans.c
+++ b/libavfilter/vf_nlmeans.c
@@ -157,6 +157,9 @@ static void compute_safe_ssd_integral_image_c(uint32_t 
*dst, int dst_linesize_32
 {
     int x, y;
 
+    /* SIMD-friendly assumptions allowed here */
+    av_assert2(!(w & 0xf) && w >= 16 && h >= 1);
+
     for (y = 0; y < h; y++) {
         uint32_t acc = dst[-1] - dst[-dst_linesize_32 - 1];
 
@@ -257,9 +260,16 @@ static void compute_ssd_integral_image(uint32_t *ii, int 
ii_linesize_32,
     // to compare the 2 sources pixels
     const int startx_safe = FFMAX(s1x, s2x);
     const int starty_safe = FFMAX(s1y, s2y);
-    const int endx_safe   = FFMIN(s1x + w, s2x + w);
+    const int u_endx_safe = FFMIN(s1x + w, s2x + w); // unaligned
     const int endy_safe   = FFMIN(s1y + h, s2y + h);
 
+    // deduce the safe area width and height
+    const int safe_pw = (u_endx_safe - startx_safe) & ~0xf;
+    const int safe_ph = endy_safe - starty_safe;
+
+    // adjusted end x position of the safe area after width of the safe area 
gets aligned
+    const int endx_safe = startx_safe + safe_pw;
+
     // top part where only one of s1 and s2 is still readable, or none at all
     compute_unsafe_ssd_integral_image(ii, ii_linesize_32,
                                       0, 0,
@@ -273,24 +283,25 @@ static void compute_ssd_integral_image(uint32_t *ii, int 
ii_linesize_32,
                                       0, starty_safe,
                                       src, linesize,
                                       offx, offy, e, w, h,
-                                      startx_safe, endy_safe - starty_safe);
+                                      startx_safe, safe_ph);
 
     // main and safe part of the integral
     av_assert1(startx_safe - s1x >= 0); av_assert1(startx_safe - s1x < w);
     av_assert1(starty_safe - s1y >= 0); av_assert1(starty_safe - s1y < h);
     av_assert1(startx_safe - s2x >= 0); av_assert1(startx_safe - s2x < w);
     av_assert1(starty_safe - s2y >= 0); av_assert1(starty_safe - s2y < h);
-    compute_safe_ssd_integral_image_c(ii + starty_safe*ii_linesize_32 + 
startx_safe, ii_linesize_32,
-                                      src + (starty_safe - s1y) * linesize + 
(startx_safe - s1x), linesize,
-                                      src + (starty_safe - s2y) * linesize + 
(startx_safe - s2x), linesize,
-                                      endx_safe - startx_safe, endy_safe - 
starty_safe);
+    if (safe_pw && safe_ph)
+        compute_safe_ssd_integral_image_c(ii + starty_safe*ii_linesize_32 + 
startx_safe, ii_linesize_32,
+                                          src + (starty_safe - s1y) * linesize 
+ (startx_safe - s1x), linesize,
+                                          src + (starty_safe - s2y) * linesize 
+ (startx_safe - s2x), linesize,
+                                          safe_pw, safe_ph);
 
     // right part of the integral
     compute_unsafe_ssd_integral_image(ii, ii_linesize_32,
                                       endx_safe, starty_safe,
                                       src, linesize,
                                       offx, offy, e, w, h,
-                                      ii_w - endx_safe, endy_safe - 
starty_safe);
+                                      ii_w - endx_safe, safe_ph);
 
     // bottom part where only one of s1 and s2 is still readable, or none at 
all
     compute_unsafe_ssd_integral_image(ii, ii_linesize_32,
-- 
2.17.0

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