daala_ec: Convert the decoder to use iCDFs

This only changes the internal coding engine. We convert CDFs into
iCDFs at the "bool" reader <-> daala_ec boundary.

Decoder output should not change.

Change-Id: I483dfe3e5588d2038c3c7ec4cd5ba62d6699b920

aom_dsp/daalaboolreader.h

diff --git a/aom_dsp/daalaboolreader.h b/aom_dsp/daalaboolreader.h
index c8271cd..29eae48 100644
--- a/aom_dsp/daalaboolreader.h
+++ b/aom_dsp/daalaboolreader.h
@@ -57,7 +57,7 @@
 }*/
 #endif
 
-  bit = od_ec_decode_bool_q15(&r->ec, p);
+  bit = od_ec_decode_bool_q15(&r->ec, OD_ICDF(p));
 
 #if CONFIG_BITSTREAM_DEBUG
   {
@@ -108,7 +108,17 @@
 
 static INLINE int daala_read_symbol(daala_reader *r, const aom_cdf_prob *cdf,
                                     int nsymbs) {
-  int symb = od_ec_decode_cdf_q15(&r->ec, cdf, nsymbs);
+  int symb;
+#if CONFIG_EC_SMALLMUL
+  {
+    aom_cdf_prob icdf[16];
+    int i;
+    for (i = 0; i < nsymbs; i++) icdf[i] = OD_ICDF(cdf[i]);
+    symb = od_ec_decode_cdf_q15(&r->ec, icdf, nsymbs);
+  }
+#else
+  symb = od_ec_decode_cdf_q15(&r->ec, cdf, nsymbs);
+#endif
 
 #if CONFIG_BITSTREAM_DEBUG
   {

aom_dsp/entdec.c

diff --git a/aom_dsp/entdec.c b/aom_dsp/entdec.c
index c539359..49b176c 100644
--- a/aom_dsp/entdec.c
+++ b/aom_dsp/entdec.c
@@ -148,24 +148,25 @@
   od_ec_dec_refill(dec);
 }
 
-/*Decode a bit that has an fz probability of being a zero in Q15.
-  fz: The probability that the bit is zero, scaled by 32768.
+/*Decode a single binary value.
+  {EC_SMALLMUL} f: The probability that the bit is one, scaled by 32768.
+  {else} f: The probability that the bit is zero, scaled by 32768.
   Return: The value decoded (0 or 1).*/
-int od_ec_decode_bool_q15(od_ec_dec *dec, unsigned fz) {
+int od_ec_decode_bool_q15(od_ec_dec *dec, unsigned f) {
   od_ec_window dif;
   od_ec_window vw;
   unsigned r;
   unsigned r_new;
   unsigned v;
   int ret;
-  OD_ASSERT(0 < fz);
-  OD_ASSERT(fz < 32768U);
+  OD_ASSERT(0 < f);
+  OD_ASSERT(f < 32768U);
   dif = dec->dif;
   r = dec->rng;
   OD_ASSERT(dif >> (OD_EC_WINDOW_SIZE - 16) < r);
   OD_ASSERT(32768U <= r);
 #if CONFIG_EC_SMALLMUL
-  v = (r >> 8) * (uint32_t)(32768U - fz) >> 7;
+  v = (r >> 8) * (uint32_t)f >> 7;
   vw = (od_ec_window)v << (OD_EC_WINDOW_SIZE - 16);
   ret = 1;
   r_new = v;
@@ -175,7 +176,7 @@
     ret = 0;
   }
 #else
-  v = fz * (uint32_t)r >> 15;
+  v = f * (uint32_t)r >> 15;
   vw = (od_ec_window)v << (OD_EC_WINDOW_SIZE - 16);
   ret = 0;
   r_new = v;
@@ -193,6 +194,7 @@
         [s > 0 ? cdf[s - 1] : 0, cdf[s]).
        The values must be monotonically non-increasing, and cdf[nsyms - 1]
         must be 32768.
+       {EC_SMALLMUL}: The CDF contains 32768 minus those values.
   nsyms: The number of symbols in the alphabet.
          This should be at most 16.
   Return: The decoded symbol s.*/
@@ -207,7 +209,7 @@
   dif = dec->dif;
   r = dec->rng;
   OD_ASSERT(dif >> (OD_EC_WINDOW_SIZE - 16) < r);
-  OD_ASSERT(cdf[nsyms - 1] == 32768U);
+  OD_ASSERT(cdf[nsyms - 1] == OD_ICDF(32768U));
   OD_ASSERT(32768U <= r);
 #if CONFIG_EC_SMALLMUL
   c = (unsigned)(dif >> (OD_EC_WINDOW_SIZE - 16));
@@ -215,7 +217,7 @@
   ret = -1;
   do {
     u = v;
-    v = (r >> 8) * (uint32_t)(32768U - cdf[++ret]) >> 7;
+    v = (r >> 8) * (uint32_t)cdf[++ret] >> 7;
   } while (c < v);
   OD_ASSERT(v < u);
   OD_ASSERT(u <= r);

aom_dsp/entdec.h

diff --git a/aom_dsp/entdec.h b/aom_dsp/entdec.h
index 9bab964..e1145e8 100644
--- a/aom_dsp/entdec.h
+++ b/aom_dsp/entdec.h
@@ -70,7 +70,7 @@
 void od_ec_dec_init(od_ec_dec *dec, const unsigned char *buf, uint32_t storage)
     OD_ARG_NONNULL(1) OD_ARG_NONNULL(2);
 
-OD_WARN_UNUSED_RESULT int od_ec_decode_bool_q15(od_ec_dec *dec, unsigned fz)
+OD_WARN_UNUSED_RESULT int od_ec_decode_bool_q15(od_ec_dec *dec, unsigned f)
     OD_ARG_NONNULL(1);
 OD_WARN_UNUSED_RESULT int od_ec_decode_cdf_q15(od_ec_dec *dec,
                                                const uint16_t *cdf, int nsyms)