All zero coeff skip in IDCT 32x32

When all coefficients are zeros, skip the corresponding 1-D inverse
transform. This practice has been used in the SSE2 implementation of
inverse 32x32 DCT. This commit imports this algorithm into the C code.

Change-Id: I0f58bfcb183a569fab85d524d5d9cf8ae8653f86

diff --git a/vp9/common/vp9_idct.c b/vp9/common/vp9_idct.c
index dea923724fed503e9fda8da294aaa3d32edbef9c..5598eb27877436f63ccb333a30d75a0ed0df6f83 100644 (file)
--- a/vp9/common/vp9_idct.c
+++ b/vp9/common/vp9_idct.c
@@ -1253,7 +1253,20 @@ void vp9_short_idct32x32_add_c(int16_t *input, uint8_t *dest, int dest_stride) {
 
   // Rows
   for (i = 0; i < 32; ++i) {
-    idct32_1d(input, outptr);
+    int16_t zero_coeff[16];
+    for (j = 0; j < 16; ++j)
+      zero_coeff[j] = input[2 * j] | input[2 * j + 1];
+    for (j = 0; j < 8; ++j)
+      zero_coeff[j] = zero_coeff[2 * j] | zero_coeff[2 * j + 1];
+    for (j = 0; j < 4; ++j)
+      zero_coeff[j] = zero_coeff[2 * j] | zero_coeff[2 * j + 1];
+    for (j = 0; j < 2; ++j)
+      zero_coeff[j] = zero_coeff[2 * j] | zero_coeff[2 * j + 1];
+
+    if (zero_coeff[0] | zero_coeff[1])
+      idct32_1d(input, outptr);
+    else
+      vpx_memset(outptr, 0, sizeof(int16_t) * 32);
     input += 32;
     outptr += 32;
   }