lavfi/dctdnoiz: move DC normalization out of loops.

Make code slightly faster, simpler, clearer.

The filter is still slow as hell, and that change won't cause any
visible performance improvement (it still takes more than one minute to
process a single 1080p frame on a Core 2 here).

libavfilter/vf_dctdnoiz.c

@@ -82,9 +82,10 @@ static float *dct_block(DCTdnoizContext *ctx, const float *src, int src_linesize
         av_dct_calc(ctx->dct, line);
 
         column = ctx->tmp_block + y;
-        for (x = 0; x < BSIZE; x++) {
+        column[0] = line[0] * (1. / sqrt(BSIZE));
-            *line *= x == 0 ? 1. / sqrt(BSIZE) : sqrt(2. / BSIZE);
+        column += BSIZE;
-            *column = *line++;
+        for (x = 1; x < BSIZE; x++) {
+            *column = line[x] * sqrt(2. / BSIZE);
             column += BSIZE;
         }
     }
@@ -92,8 +93,9 @@ static float *dct_block(DCTdnoizContext *ctx, const float *src, int src_linesize
     column = ctx->tmp_block;
     for (x = 0; x < BSIZE; x++) {
         av_dct_calc(ctx->dct, column);
-        for (y = 0; y < BSIZE; y++)
+        column[0] *= 1. / sqrt(BSIZE);
-            column[y] *= y == 0 ? 1. / sqrt(BSIZE) : sqrt(2. / BSIZE);
+        for (y = 1; y < BSIZE; y++)
+            column[y] *= sqrt(2. / BSIZE);
         column += BSIZE;
     }
 
@@ -111,18 +113,18 @@ static void idct_block(DCTdnoizContext *ctx, float *dst, int dst_linesize)
     float *tmp = ctx->tmp_block;
 
     for (y = 0; y < BSIZE; y++) {
-        for (x = 0; x < BSIZE; x++)
+        block[0] *= sqrt(BSIZE);
-            block[x] *= x == 0 ? sqrt(BSIZE) : 1./sqrt(2. / BSIZE);
+        for (x = 1; x < BSIZE; x++)
+            block[x] *= 1./sqrt(2. / BSIZE);
         av_dct_calc(ctx->idct, block);
         block += BSIZE;
     }
 
     block = ctx->block;
     for (y = 0; y < BSIZE; y++) {
-        for (x = 0; x < BSIZE; x++) {
+        tmp[0] = block[y] * sqrt(BSIZE);
-            tmp[x] = block[x*BSIZE + y];
+        for (x = 1; x < BSIZE; x++)
-            tmp[x] *= x == 0 ? sqrt(BSIZE) : 1./sqrt(2. / BSIZE);
+            tmp[x] = block[x*BSIZE + y] * (1./sqrt(2. / BSIZE));
-        }
         av_dct_calc(ctx->idct, tmp);
         for (x = 0; x < BSIZE; x++)
             dst[x*dst_linesize + y] += tmp[x];