shithub: dav1d

--- a/src/decode.c

+++ b/src/decode.c

@@ -413,7 +413,7 @@

     // find reused cache entries

     int i = 0;

     for (int n = 0; n < n_cache && i < pal_sz; n++)

-        if (msac_decode_bool(&ts->msac, EC_BOOL_EPROB))

+        if (msac_decode_bool_equi(&ts->msac))

             used_cache[i++] = cache[n];

     const int n_used_cache = i;

@@ -477,13 +477,13 @@

     uint16_t *const pal = f->frame_thread.pass ?

         f->frame_thread.pal[((t->by >> 1) + (t->bx & 1)) * (f->b4_stride >> 1) +

                             ((t->bx >> 1) + (t->by & 1))][2] : t->pal[2];

-    if (msac_decode_bool(&ts->msac, EC_BOOL_EPROB)) {

+    if (msac_decode_bool_equi(&ts->msac)) {

         const int bits = f->cur.p.bpc - 4 + msac_decode_bools(&ts->msac, 2);

         int prev = pal[0] = msac_decode_bools(&ts->msac, f->cur.p.bpc);

         const int max = (1 << f->cur.p.bpc) - 1;

         for (int i = 1; i < b->pal_sz[1]; i++) {

             int delta = msac_decode_bools(&ts->msac, bits);

-            if (delta && msac_decode_bool(&ts->msac, EC_BOOL_EPROB)) delta = -delta;

+            if (delta && msac_decode_bool_equi(&ts->msac)) delta = -delta;

             prev = pal[i] = (prev + delta) & max;

     } else {

@@ -927,7 +927,7 @@

                 delta_q = msac_decode_bools(&ts->msac, n_bits) + 1 + (1 << n_bits);

             if (delta_q) {

-                if (msac_decode_bool(&ts->msac, EC_BOOL_EPROB)) delta_q = -delta_q;

+                if (msac_decode_bool_equi(&ts->msac)) delta_q = -delta_q;

                 delta_q *= 1 << f->frame_hdr->delta.q.res_log2;

             ts->last_qidx = iclip(ts->last_qidx + delta_q, 1, 255);

@@ -949,7 +949,7 @@

                                    1 + (1 << n_bits);

                     if (delta_lf) {

-                        if (msac_decode_bool(&ts->msac, EC_BOOL_EPROB))

+                        if (msac_decode_bool_equi(&ts->msac))

                             delta_lf = -delta_lf;

                         delta_lf *= 1 << f->frame_hdr->delta.lf.res_log2;

@@ -1572,7 +1572,7 @@

                 } else {

                     b->comp_type = COMP_INTER_SEG;

-                b->mask_sign = msac_decode_bool(&ts->msac, EC_BOOL_EPROB);

+                b->mask_sign = msac_decode_bool_equi(&ts->msac);

                 if (DEBUG_BLOCK_INFO)

                     printf("Post-seg/wedge[%d,wedge_idx=%d,sign=%d]: r=%d\n",

                            b->comp_type == COMP_INTER_WEDGE,

--- a/src/msac.c

+++ b/src/msac.c

@@ -91,6 +91,22 @@

     return ret - 1;

+unsigned msac_decode_bool_equi(MsacContext *const s) {

+    ec_win v, vw, dif = s->dif;

+    uint16_t r = s->rng;

+    unsigned ret;

+    assert((dif >> (EC_WIN_SIZE - 16)) < r);

+    // When the probability is 1/2, f = 16384 >> EC_PROB_SHIFT = 256 and we can

+    // replace the multiply with a simple shift.

+    v = ((r >> 8) << 7) + EC_MIN_PROB;

+    vw   = v << (EC_WIN_SIZE - 16);

+    ret  = dif >= vw;

+    dif -= ret*vw;

+    v   += ret*(r - 2*v);

+    ctx_norm(s, dif, v);

+    return !ret;

+}

 /* Decode a single binary value.

  * f: The probability that the bit is one

  * Return: The value decoded (0 or 1). */

@@ -111,7 +127,7 @@

 unsigned msac_decode_bools(MsacContext *const c, const unsigned l) {

     int v = 0;

     for (int n = (int) l - 1; n >= 0; n--)

-        v = (v << 1) | msac_decode_bool(c, EC_BOOL_EPROB);

+        v = (v << 1) | msac_decode_bool_equi(c);

     return v;

@@ -122,7 +138,7 @@

     int a = 0;

     int b = k;

     while ((2 << b) < n) {

-        if (!msac_decode_bool(c, EC_BOOL_EPROB)) break;

+        if (!msac_decode_bool_equi(c)) break;

         b = k + i++;

         a = (1 << b);

@@ -137,7 +153,7 @@

     assert(l > 1);

     const unsigned m = (1 << l) - n;

     const unsigned v = msac_decode_bools(c, l - 1);

-    return v < m ? v : (v << 1) - m + msac_decode_bool(c, EC_BOOL_EPROB);

+    return v < m ? v : (v << 1) - m + msac_decode_bool_equi(c);

 static void update_cdf(uint16_t *const cdf, const unsigned val,

--- a/src/msac.h

+++ b/src/msac.h

@@ -44,7 +44,6 @@

 } MsacContext;

 #define EC_PROB_SHIFT 6

-#define EC_BOOL_EPROB 256

 void msac_init(MsacContext *c, const uint8_t *data, size_t sz, int disable_cdf_update_flag);

 unsigned msac_decode_symbol(MsacContext *s, const uint16_t *cdf,

@@ -51,6 +50,7 @@

                             const unsigned n_symbols);

 unsigned msac_decode_symbol_adapt(MsacContext *s, uint16_t *cdf,

                                   const unsigned n_symbols);

+unsigned msac_decode_bool_equi(MsacContext *const s);

 unsigned msac_decode_bool(MsacContext *s, unsigned f);

 unsigned msac_decode_bool_adapt(MsacContext *s, uint16_t *cdf);

 unsigned msac_decode_bools(MsacContext *c, unsigned l);

--- a/src/recon_tmpl.c

+++ b/src/recon_tmpl.c

@@ -50,8 +50,8 @@

     int len = 0;

     unsigned val = 1;

-    while (!msac_decode_bool(msac, EC_BOOL_EPROB) && len < 32) len++;

-    while (len--) val = (val << 1) | msac_decode_bool(msac, EC_BOOL_EPROB);

+    while (!msac_decode_bool_equi(msac) && len < 32) len++;

+    while (len--) val = (val << 1) | msac_decode_bool_equi(msac);

     return val - 1;

@@ -152,7 +152,7 @@

         unsigned mask = eob >> 1;

         if (eob_hi_bit) eob |= mask;

         for (mask >>= 1; mask; mask >>= 1) {

-            const int eob_bit = msac_decode_bool(&ts->msac, EC_BOOL_EPROB);

+            const int eob_bit = msac_decode_bool_equi(&ts->msac);

             if (eob_bit) eob |= mask;

         if (dbg)

@@ -231,7 +231,7 @@

             dc_sign = sign ? 0 : 2;

             dq = (dq_tbl[0] * qm_tbl[0] + 16) >> 5;

         } else {

-            sign = msac_decode_bool(&ts->msac, EC_BOOL_EPROB);

+            sign = msac_decode_bool_equi(&ts->msac);

             if (dbg)

             printf("Post-sign[%d=%d=%d]: r=%d\n", i, rc, sign, ts->msac.rng);

             dq = (dq_tbl[1] * qm_tbl[rc] + 16) >> 5;