ref: f4bee75c2b03901d789b2d70d72db5802932656d
dir: /vp9/encoder/vp9_subexp.c/
/*
* Copyright (c) 2013 The WebM project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "vp9/common/vp9_common.h"
#include "vp9/common/vp9_entropy.h"
#include "vp9/encoder/vp9_boolhuff.h"
#include "vp9/encoder/vp9_treewriter.h"
#define vp9_cost_upd ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)) >> 8)
#define vp9_cost_upd256 ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)))
static int update_bits[255];
static int count_uniform(int v, int n) {
int l = get_unsigned_bits(n);
int m;
if (l == 0) return 0;
m = (1 << l) - n;
if (v < m)
return l - 1;
else
return l;
}
static int split_index(int i, int n, int modulus) {
int max1 = (n - 1 - modulus / 2) / modulus + 1;
if (i % modulus == modulus / 2)
i = i / modulus;
else
i = max1 + i - (i + modulus - modulus / 2) / modulus;
return i;
}
static int recenter_nonneg(int v, int m) {
if (v > (m << 1))
return v;
else if (v >= m)
return ((v - m) << 1);
else
return ((m - v) << 1) - 1;
}
static int remap_prob(int v, int m) {
const int n = 255;
const int modulus = MODULUS_PARAM;
int i;
v--;
m--;
if ((m << 1) <= n)
i = recenter_nonneg(v, m) - 1;
else
i = recenter_nonneg(n - 1 - v, n - 1 - m) - 1;
i = split_index(i, n - 1, modulus);
return i;
}
static int count_term_subexp(int word, int k, int num_syms) {
int count = 0;
int i = 0;
int mk = 0;
while (1) {
int b = (i ? k + i - 1 : k);
int a = (1 << b);
if (num_syms <= mk + 3 * a) {
count += count_uniform(word - mk, num_syms - mk);
break;
} else {
int t = (word >= mk + a);
count++;
if (t) {
i = i + 1;
mk += a;
} else {
count += b;
break;
}
}
}
return count;
}
static int prob_diff_update_cost(vp9_prob newp, vp9_prob oldp) {
int delp = remap_prob(newp, oldp);
return update_bits[delp] * 256;
}
static void encode_uniform(vp9_writer *w, int v, int n) {
int l = get_unsigned_bits(n);
int m;
if (l == 0)
return;
m = (1 << l) - n;
if (v < m) {
vp9_write_literal(w, v, l - 1);
} else {
vp9_write_literal(w, m + ((v - m) >> 1), l - 1);
vp9_write_literal(w, (v - m) & 1, 1);
}
}
static void encode_term_subexp(vp9_writer *w, int word, int k, int num_syms) {
int i = 0;
int mk = 0;
while (1) {
int b = (i ? k + i - 1 : k);
int a = (1 << b);
if (num_syms <= mk + 3 * a) {
encode_uniform(w, word - mk, num_syms - mk);
break;
} else {
int t = (word >= mk + a);
vp9_write_literal(w, t, 1);
if (t) {
i = i + 1;
mk += a;
} else {
vp9_write_literal(w, word - mk, b);
break;
}
}
}
}
void vp9_write_prob_diff_update(vp9_writer *w, vp9_prob newp, vp9_prob oldp) {
const int delp = remap_prob(newp, oldp);
encode_term_subexp(w, delp, SUBEXP_PARAM, 255);
}
void vp9_compute_update_table() {
int i;
for (i = 0; i < 254; i++)
update_bits[i] = count_term_subexp(i, SUBEXP_PARAM, 255);
}
int vp9_prob_diff_update_savings_search(const unsigned int *ct,
vp9_prob oldp, vp9_prob *bestp,
vp9_prob upd) {
const int old_b = cost_branch256(ct, oldp);
int bestsavings = 0;
vp9_prob newp, bestnewp = oldp;
const int step = *bestp > oldp ? -1 : 1;
for (newp = *bestp; newp != oldp; newp += step) {
const int new_b = cost_branch256(ct, newp);
const int update_b = prob_diff_update_cost(newp, oldp) + vp9_cost_upd256;
const int savings = old_b - new_b - update_b;
if (savings > bestsavings) {
bestsavings = savings;
bestnewp = newp;
}
}
*bestp = bestnewp;
return bestsavings;
}
int vp9_prob_diff_update_savings_search_model(const unsigned int *ct,
const vp9_prob *oldp,
vp9_prob *bestp,
vp9_prob upd,
int b, int r) {
int i, old_b, new_b, update_b, savings, bestsavings, step;
int newp;
vp9_prob bestnewp, newplist[ENTROPY_NODES], oldplist[ENTROPY_NODES];
vp9_model_to_full_probs(oldp, oldplist);
vpx_memcpy(newplist, oldp, sizeof(vp9_prob) * UNCONSTRAINED_NODES);
for (i = UNCONSTRAINED_NODES, old_b = 0; i < ENTROPY_NODES; ++i)
old_b += cost_branch256(ct + 2 * i, oldplist[i]);
old_b += cost_branch256(ct + 2 * PIVOT_NODE, oldplist[PIVOT_NODE]);
bestsavings = 0;
bestnewp = oldp[PIVOT_NODE];
step = (*bestp > oldp[PIVOT_NODE] ? -1 : 1);
for (newp = *bestp; newp != oldp[PIVOT_NODE]; newp += step) {
if (newp < 1 || newp > 255)
continue;
newplist[PIVOT_NODE] = newp;
vp9_model_to_full_probs(newplist, newplist);
for (i = UNCONSTRAINED_NODES, new_b = 0; i < ENTROPY_NODES; ++i)
new_b += cost_branch256(ct + 2 * i, newplist[i]);
new_b += cost_branch256(ct + 2 * PIVOT_NODE, newplist[PIVOT_NODE]);
update_b = prob_diff_update_cost(newp, oldp[PIVOT_NODE]) +
vp9_cost_upd256;
savings = old_b - new_b - update_b;
if (savings > bestsavings) {
bestsavings = savings;
bestnewp = newp;
}
}
*bestp = bestnewp;
return bestsavings;
}
void vp9_cond_prob_diff_update(vp9_writer *w, vp9_prob *oldp,
vp9_prob upd, unsigned int *ct) {
vp9_prob newp = get_binary_prob(ct[0], ct[1]);
const int savings = vp9_prob_diff_update_savings_search(ct, *oldp, &newp,
upd);
assert(newp >= 1);
if (savings > 0) {
vp9_write(w, 1, upd);
vp9_write_prob_diff_update(w, newp, *oldp);
*oldp = newp;
} else {
vp9_write(w, 0, upd);
}
}