shithub: dav1d

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Remove confusing math and redundant computations.

--- a/src/env.h

+++ b/src/env.h

@@ -91,35 +91,34 @@

 }

 static inline unsigned cdf_element_prob(const uint16_t *const cdf, const int e) {

-    return (e > 0 ? cdf[e - 1] : 32768) - cdf[e];

+    assert(e > 0);

+    return cdf[e - 1] - cdf[e];

 }

 static inline unsigned gather_left_partition_prob(const uint16_t *const in,

                                                   const enum BlockLevel bl)

 {

-    unsigned out = 32768;

-    out -= cdf_element_prob(in, PARTITION_H);

+    unsigned out = 0;

+    out += cdf_element_prob(in, PARTITION_H);

     if (bl != BL_128X128)

-        out -= cdf_element_prob(in, PARTITION_H4);

-    out -= cdf_element_prob(in, PARTITION_SPLIT);

-    out -= cdf_element_prob(in, PARTITION_T_TOP_SPLIT);

-    out -= cdf_element_prob(in, PARTITION_T_BOTTOM_SPLIT);

-    out -= cdf_element_prob(in, PARTITION_T_LEFT_SPLIT);

-    return 32768 - out;

+        out += cdf_element_prob(in, PARTITION_H4);

+    // Exploit the fact that cdfs for PARTITION_SPLIT, PARTITION_T_TOP_SPLIT,

+    //  PARTITION_T_BOTTOM_SPLIT and PARTITION_T_LEFT_SPLIT are neighbors.

+    out += in[PARTITION_SPLIT - 1] - in[PARTITION_T_LEFT_SPLIT];

+    return out;

 }

 static inline unsigned gather_top_partition_prob(const uint16_t *const in,

                                                  const enum BlockLevel bl)

 {

-    unsigned out = 32768;

-    out -= cdf_element_prob(in, PARTITION_V);

+    unsigned out = 0;

     if (bl != BL_128X128)

-        out -= cdf_element_prob(in, PARTITION_V4);

-    out -= cdf_element_prob(in, PARTITION_SPLIT);

-    out -= cdf_element_prob(in, PARTITION_T_TOP_SPLIT);

-    out -= cdf_element_prob(in, PARTITION_T_LEFT_SPLIT);

-    out -= cdf_element_prob(in, PARTITION_T_RIGHT_SPLIT);

-    return 32768 - out;

+        out += cdf_element_prob(in, PARTITION_V4);

+    // Exploit the fact that cdfs for PARTITION_T_LEFT_SPLIT and PARTITION_T_RIGHT_SPLIT,

+    //  and PARTITION_V, PARTITION_SPLIT and PARTITION_T_TOP_SPLIT are neighbors.

+    out += in[PARTITION_T_LEFT_SPLIT - 1] - in[PARTITION_T_RIGHT_SPLIT];

+    out += in[PARTITION_V - 1] - in[PARTITION_T_TOP_SPLIT];

+    return out;

 }

 static inline enum TxfmTypeSet get_ext_txtp_set(const enum RectTxfmSize tx,