swscale: fix gbrap16 alpha channel issues

Fixes filter-pixfmts-scale test failing on big-endian systems due to
alpSrc not being cast to (const int32_t**).

Also fixes distortions in the output alpha channel values by copying the
alpha channel code from the rgba64 case found elsewhere in output.c.

Fixes ticket 6555.

Signed-off-by: James Cowgill <James.Cowgill@imgtec.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/output.c

@@ -2026,24 +2026,24 @@ yuv2gbrp16_full_X_c(SwsContext *c, const int16_t *lumFilter,
                     const int16_t **lumSrcx, int lumFilterSize,
                     const int16_t *chrFilter, const int16_t **chrUSrcx,
                     const int16_t **chrVSrcx, int chrFilterSize,
-                    const int16_t **alpSrc, uint8_t **dest,
+                    const int16_t **alpSrcx, uint8_t **dest,
                     int dstW, int y)
 {
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(c->dstFormat);
     int i;
-    int hasAlpha = (desc->flags & AV_PIX_FMT_FLAG_ALPHA) && alpSrc;
+    int hasAlpha = (desc->flags & AV_PIX_FMT_FLAG_ALPHA) && alpSrcx;
     uint16_t **dest16 = (uint16_t**)dest;
     const int32_t **lumSrc  = (const int32_t**)lumSrcx;
     const int32_t **chrUSrc = (const int32_t**)chrUSrcx;
     const int32_t **chrVSrc = (const int32_t**)chrVSrcx;
-    int A = 0; // init to silence warning
+    const int32_t **alpSrc  = (const int32_t**)alpSrcx;
 
     for (i = 0; i < dstW; i++) {
         int j;
         int Y = -0x40000000;
         int U = -(128 << 23);
         int V = -(128 << 23);
-        int R, G, B;
+        int R, G, B, A;
 
         for (j = 0; j < lumFilterSize; j++)
             Y += lumSrc[j][i] * (unsigned)lumFilter[j];
@@ -2059,13 +2059,13 @@ yuv2gbrp16_full_X_c(SwsContext *c, const int16_t *lumFilter,
         V >>= 14;
 
         if (hasAlpha) {
-            A = 1 << 18;
+            A = -0x40000000;
 
             for (j = 0; j < lumFilterSize; j++)
                 A += alpSrc[j][i] * lumFilter[j];
 
-            if (A & 0xF8000000)
-                A =  av_clip_uintp2(A, 27);
+            A >>= 1;
+            A += 0x20002000;
         }
 
         Y -= c->yuv2rgb_y_offset;
@@ -2083,7 +2083,7 @@ yuv2gbrp16_full_X_c(SwsContext *c, const int16_t *lumFilter,
         dest16[1][i] = B >> 14;
         dest16[2][i] = R >> 14;
         if (hasAlpha)
-            dest16[3][i] = A >> 11;
+            dest16[3][i] = av_clip_uintp2(A, 30) >> 14;
     }
     if ((!isBE(c->dstFormat)) != (!HAVE_BIGENDIAN)) {
         for (i = 0; i < dstW; i++) {

tests/ref/fate/filter-pixfmts-scale

@@ -23,8 +23,8 @@ gbrap10be           6d89abb9248006c3e9017545e9474654
 gbrap10le           cf974e23f485a10740f5de74a5c8c3df
 gbrap12be           1d9b57766ba9c2192403f43967cb9af0
 gbrap12le           bb1ba1c157717db3dd612a76d38a018e
-gbrap16be           81542b96575d1fe3b239d23899f5ece3
-gbrap16le           6feb8b9da131917abe867e0eaaf07b90
+gbrap16be           c72b935a6e57a8e1c37bff08c2db55b1
+gbrap16le           13eb0e62b1ac9c1c86c81521eaefab5f
 gbrp                dc3387f925f972c61aae7eb23cdc19f0
 gbrp10be            0277d4c3a8498d75e2783fb81379e481
 gbrp10le            f3d70f8ab845c3c9b8f7452e4a6e285a