avfilter/vf_spp: Fix overflow in 8bit store slice

Fixes regression with
ffplay -f lavfi -i testsrc=640x480  -vf format=gray,boxblur=20:10,geq="'mod(lum(X,Y),16)*15'",boxblur=10,geq="'abs(mod(lum(X,Y),15)-7)*32'",spp=4:40
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_spp.c

@@ -156,7 +156,7 @@ static void softthresh_c(int16_t dst[64], const int16_t src[64],
     }
 }
 
-static void store_slice_c(uint8_t *dst, const uint16_t *src,
+static void store_slice_c(uint8_t *dst, const int16_t *src,
                           int dst_linesize, int src_linesize,
                           int width, int height, int log2_scale,
                           const uint8_t dither[8][8])

libavfilter/vf_spp.h

@@ -45,7 +45,7 @@ typedef struct {
     int use_bframe_qp;
     int hsub, vsub;
 
-    void (*store_slice)(uint8_t *dst, const uint16_t *src,
+    void (*store_slice)(uint8_t *dst, const int16_t *src,
                         int dst_stride, int src_stride,
                         int width, int height, int log2_scale,
                         const uint8_t dither[8][8]);

libavfilter/x86/vf_spp.c

@@ -174,7 +174,7 @@ static void softthresh_mmx(int16_t dst[64], const int16_t src[64],
     dst[0] = (src[0] + 4) >> 3;
 }
 
-static void store_slice_mmx(uint8_t *dst, const uint16_t *src,
+static void store_slice_mmx(uint8_t *dst, const int16_t *src,
                             int dst_stride, int src_stride,
                             int width, int height, int log2_scale,
                             const uint8_t dither[8][8])