vp9dsp: add DC only versions for idct/idct.

before:

time ./avconv -v 0 -nostats -threads 1 -i sintel_vp9_500kbps.webm -f null -
real    0m11.125s
user    0m11.059s
sys     0m0.050s

time ./avconv -v 0 -nostats -threads 1 -i sintel_vp9_500kbps.webm -f null -
real    0m10.944s
user    0m10.819s
sys     0m0.064s

after:

time ./avconv -v 0 -nostats -threads 1 -i sintel_vp9_500kbps.webm -f null -
real    0m8.153s
user    0m8.034s
sys     0m0.050s

time ./avconv -v 0 -nostats -threads 1 -i sintel_vp9_500kbps.webm -f null -
real    0m8.038s
user    0m7.980s
sys     0m0.039s
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/vp9dsp.c

@@ -944,7 +944,7 @@ static av_cold void vp9dsp_intrapred_init(VP9DSPContext *dsp)
 #undef init_intra_pred
 }
 
-#define itxfm_wrapper(type_a, type_b, sz, bits)                             \
+#define itxfm_wrapper(type_a, type_b, sz, bits, has_dconly)                 \
 static void                                                                 \
 type_a ## _ ## type_b ## _ ## sz ## x ## sz ## _add_c(uint8_t *dst,         \
                                                       ptrdiff_t stride,     \
@@ -953,6 +953,22 @@ type_a ## _ ## type_b ## _ ## sz ## x ## sz ## _add_c(uint8_t *dst,         \
 {                                                                           \
     int i, j;                                                               \
     int16_t tmp[sz * sz], out[sz];                                          \
+                                                                            \
+    if (has_dconly && eob == 1) {                                           \
+        const int t  = (((block[0] * 11585 + (1 << 13)) >> 14)              \
+                                   * 11585 + (1 << 13)) >> 14;              \
+        block[0] = 0;                                                       \
+        for (i = 0; i < sz; i++) {                                          \
+            for (j = 0; j < sz; j++)                                        \
+                dst[j * stride] =                                           \
+                    av_clip_uint8(dst[j * stride] +                         \
+                                  (bits ? (t + (1 << (bits - 1))) >> bits   \
+                                        : t));                              \
+            dst++;                                                          \
+        }                                                                   \
+        return;                                                             \
+    }                                                                       \
+                                                                            \
     for (i = 0; i < sz; i++)                                                \
         type_a ## sz ## _1d(tmp + i * sz, block + i, sz, 0);                \
     memset(block, 0, sz * sz * sizeof(*block));                             \
@@ -967,11 +983,11 @@ type_a ## _ ## type_b ## _ ## sz ## x ## sz ## _add_c(uint8_t *dst,         \
     }                                                                       \
 }
 
-#define itxfm_wrap(sz, bits)             \
-    itxfm_wrapper(idct, idct, sz, bits)  \
-    itxfm_wrapper(iadst, idct, sz, bits) \
-    itxfm_wrapper(idct, iadst, sz, bits) \
-    itxfm_wrapper(iadst, iadst, sz, bits)
+#define itxfm_wrap(sz, bits)                 \
+    itxfm_wrapper(idct,  idct,  sz, bits, 1) \
+    itxfm_wrapper(iadst, idct,  sz, bits, 0) \
+    itxfm_wrapper(idct,  iadst, sz, bits, 0) \
+    itxfm_wrapper(iadst, iadst, sz, bits, 0)
 
 #define IN(x) in[x * stride]
 
@@ -1490,7 +1506,7 @@ static av_always_inline void idct32_1d(int16_t *out, const int16_t *in,
     out[31] = t0   - t31;
 }
 
-itxfm_wrapper(idct, idct, 32, 6)
+itxfm_wrapper(idct, idct, 32, 6, 1)
 
 static av_always_inline void iwht4_1d(int16_t *out, const int16_t *in,
                                       ptrdiff_t stride, int pass)
@@ -1523,7 +1539,7 @@ static av_always_inline void iwht4_1d(int16_t *out, const int16_t *in,
     out[3] = t3;
 }
 
-itxfm_wrapper(iwht, iwht, 4, 0)
+itxfm_wrapper(iwht, iwht, 4, 0, 0)
 
 #undef IN
 #undef itxfm_wrapper