7-bit interpolation filters

Purpose:
-Reduce dynamic range of interpolation filter coefficents from 8
bits to 7 bits.
-Inner product for 8-bit input data can be stored in a 16-bit signed
integer.

Impact on compression efficiency:
-Marginal improvement, typically less than 0.5% BDR.

Change-Id: I58d1408307ae7d2a6f9de8965c5877b258703199

av1/common/filter.c

diff --git a/av1/common/filter.c b/av1/common/filter.c
index f653c6d..573f51a 100644
--- a/av1/common/filter.c
+++ b/av1/common/filter.c
@@ -28,6 +28,16 @@
 // Lagrangian interpolation filter
 DECLARE_ALIGNED(256, static const int16_t,
                 sub_pel_filters_8[SUBPEL_SHIFTS][8]) = {
+#if CONFIG_FILTER_7BIT
+  { 0, 0, 0, 128, 0, 0, 0, 0 },      { 0, 2, -6, 126, 8, -2, 0, 0 },
+  { 0, 2, -10, 122, 18, -4, 0, 0 },  { 0, 2, -12, 116, 28, -8, 2, 0 },
+  { 0, 2, -14, 110, 38, -10, 2, 0 }, { 0, 2, -14, 102, 48, -12, 2, 0 },
+  { 0, 2, -16, 94, 58, -12, 2, 0 },  { 0, 2, -14, 84, 66, -12, 2, 0 },
+  { 0, 2, -14, 76, 76, -14, 2, 0 },  { 0, 2, -12, 66, 84, -14, 2, 0 },
+  { 0, 2, -12, 58, 94, -16, 2, 0 },  { 0, 2, -12, 48, 102, -14, 2, 0 },
+  { 0, 2, -10, 38, 110, -14, 2, 0 }, { 0, 2, -8, 28, 116, -12, 2, 0 },
+  { 0, 0, -4, 18, 122, -10, 2, 0 },  { 0, 0, -2, 8, 126, -6, 2, 0 }
+#else
   { 0, 0, 0, 128, 0, 0, 0, 0 },        { 0, 1, -5, 126, 8, -3, 1, 0 },
   { -1, 3, -10, 122, 18, -6, 2, 0 },   { -1, 4, -13, 118, 27, -9, 3, -1 },
   { -1, 4, -16, 112, 37, -11, 4, -1 }, { -1, 5, -18, 105, 48, -14, 4, -1 },
@@ -36,11 +46,22 @@
   { -1, 5, -16, 58, 97, -19, 5, -1 },  { -1, 4, -14, 48, 105, -18, 5, -1 },
   { -1, 4, -11, 37, 112, -16, 4, -1 }, { -1, 3, -9, 27, 118, -13, 4, -1 },
   { 0, 2, -6, 18, 122, -10, 3, -1 },   { 0, 1, -3, 8, 126, -5, 1, 0 }
+#endif
 };
 
 // DCT based filter
 DECLARE_ALIGNED(256, static const int16_t,
                 sub_pel_filters_8sharp[SUBPEL_SHIFTS][8]) = {
+#if CONFIG_FILTER_7BIT
+  { 0, 0, 0, 128, 0, 0, 0, 0 },         { -2, 2, -6, 126, 8, -2, 2, 0 },
+  { -2, 6, -12, 124, 16, -6, 4, -2 },   { -2, 8, -18, 120, 26, -10, 6, -2 },
+  { -4, 10, -22, 116, 38, -14, 6, -2 }, { -4, 10, -22, 108, 48, -18, 8, -2 },
+  { -4, 10, -24, 100, 60, -20, 8, -2 }, { -4, 10, -24, 90, 70, -22, 10, -2 },
+  { -4, 12, -24, 80, 80, -24, 12, -4 }, { -2, 10, -22, 70, 90, -24, 10, -4 },
+  { -2, 8, -20, 60, 100, -24, 10, -4 }, { -2, 8, -18, 48, 108, -22, 10, -4 },
+  { -2, 6, -14, 38, 116, -22, 10, -4 }, { -2, 6, -10, 26, 120, -18, 8, -2 },
+  { -2, 4, -6, 16, 124, -12, 6, -2 },   { 0, 2, -2, 8, 126, -6, 2, -2 }
+#else
   { 0, 0, 0, 128, 0, 0, 0, 0 },         { -1, 3, -7, 127, 8, -3, 1, 0 },
   { -2, 5, -13, 125, 17, -6, 3, -1 },   { -3, 7, -17, 121, 27, -10, 5, -2 },
   { -4, 9, -20, 115, 37, -13, 6, -2 },  { -4, 10, -23, 108, 48, -16, 8, -3 },
@@ -49,7 +70,9 @@
   { -3, 9, -19, 59, 100, -24, 10, -4 }, { -3, 8, -16, 48, 108, -23, 10, -4 },
   { -2, 6, -13, 37, 115, -20, 9, -4 },  { -2, 5, -10, 27, 121, -17, 7, -3 },
   { -1, 3, -6, 17, 125, -13, 5, -2 },   { 0, 1, -3, 8, 127, -7, 3, -1 }
+#endif
 };
+
 #if CONFIG_EXT_INTERP
 DECLARE_ALIGNED(256, static const int16_t,
                 sub_pel_filters_10sharp[SUBPEL_SHIFTS][10]) = {
@@ -124,6 +147,16 @@
 // freqmultiplier = 0.5
 DECLARE_ALIGNED(256, static const int16_t,
                 sub_pel_filters_8smooth[SUBPEL_SHIFTS][8]) = {
+#if CONFIG_FILTER_7BIT
+  { 0, 0, 0, 128, 0, 0, 0, 0 },     { 0, 2, 28, 62, 34, 2, 0, 0 },
+  { 0, 0, 26, 62, 36, 4, 0, 0 },    { 0, 0, 22, 62, 40, 4, 0, 0 },
+  { 0, 0, 20, 60, 42, 6, 0, 0 },    { 0, 0, 18, 58, 44, 8, 0, 0 },
+  { 0, 0, 16, 56, 46, 10, 0, 0 },   { 0, -2, 16, 54, 48, 12, 0, 0 },
+  { 0, -2, 14, 52, 52, 14, -2, 0 }, { 0, 0, 12, 48, 54, 16, -2, 0 },
+  { 0, 0, 10, 46, 56, 16, 0, 0 },   { 0, 0, 8, 44, 58, 18, 0, 0 },
+  { 0, 0, 6, 42, 60, 20, 0, 0 },    { 0, 0, 4, 40, 62, 22, 0, 0 },
+  { 0, 0, 4, 36, 62, 26, 0, 0 },    { 0, 0, 2, 34, 62, 28, 2, 0 }
+#else
   { 0, 0, 0, 128, 0, 0, 0, 0 },       { -3, -1, 32, 64, 38, 1, -3, 0 },
   { -2, -2, 29, 63, 41, 2, -3, 0 },   { -2, -2, 26, 63, 43, 4, -4, 0 },
   { -2, -3, 24, 62, 46, 5, -4, 0 },   { -2, -3, 21, 60, 49, 7, -4, 0 },
@@ -132,6 +165,7 @@
   { 0, -4, 9, 51, 59, 18, -4, -1 },   { 0, -4, 7, 49, 60, 21, -3, -2 },
   { 0, -4, 5, 46, 62, 24, -3, -2 },   { 0, -4, 4, 43, 63, 26, -2, -2 },
   { 0, -3, 2, 41, 63, 29, -2, -2 },   { 0, -3, 1, 38, 64, 32, -1, -3 }
+#endif
 };
 
 #endif  // CONFIG_EXT_INTERP

configure

diff --git a/configure b/configure
index 9e1e05b..1e716d2 100755
--- a/configure
+++ b/configure
@@ -269,6 +269,7 @@
     cb4x4
     palette
     frame_size
+    filter_7bit
 "
 CONFIG_LIST="
     dependency_tracking