Alpha: proper IDCT selection

Only select the Alpha IDCT if auto or explicitly requested.  Also
disable it in lowres mode.

Originally committed as revision 16666 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/alpha/dsputil_alpha.c

@@ -356,7 +356,11 @@ void dsputil_init_alpha(DSPContext* c, AVCodecContext *avctx)
     put_pixels_clamped_axp_p = c->put_pixels_clamped;
     add_pixels_clamped_axp_p = c->add_pixels_clamped;
 
+    if (!avctx->lowres &&
+        (avctx->idct_algo == FF_IDCT_AUTO ||
+         avctx->idct_algo == FF_IDCT_SIMPLEALPHA)) {
     c->idct_put = simple_idct_put_axp;
     c->idct_add = simple_idct_add_axp;
     c->idct = simple_idct_axp;
+    }
 }

libavcodec/avcodec.h

@@ -1398,6 +1398,7 @@ typedef struct AVCodecContext {
 #define FF_IDCT_FAAN          20
 #define FF_IDCT_EA            21
 #define FF_IDCT_SIMPLENEON    22
+#define FF_IDCT_SIMPLEALPHA   23
 
     /**
      * slice count

libavcodec/options.c

@@ -210,6 +210,7 @@ static const AVOption options[]={
 {"simplearmv5te", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_SIMPLEARMV5TE, INT_MIN, INT_MAX, V|E|D, "idct"},
 {"simplearmv6", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_SIMPLEARMV6, INT_MIN, INT_MAX, V|E|D, "idct"},
 {"simpleneon", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_SIMPLENEON, INT_MIN, INT_MAX, V|E|D, "idct"},
+{"simplealpha", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_SIMPLEALPHA, INT_MIN, INT_MAX, V|E|D, "idct"},
 {"h264", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_H264, INT_MIN, INT_MAX, V|E|D, "idct"},
 {"vp3", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_VP3, INT_MIN, INT_MAX, V|E|D, "idct"},
 {"ipp", NULL, 0, FF_OPT_TYPE_CONST, FF_IDCT_IPP, INT_MIN, INT_MAX, V|E|D, "idct"},