media/libvpx/vp9/encoder/vp9_subexp.c@ac0c01689b40
media/libvpx/vp9/encoder/vp9_subexp.c
Thu, 15 Jan 2015 15:59:08 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Thu, 15 Jan 2015 15:59:08 +0100
- branch
- TOR_BUG_9701
- changeset 10
- ac0c01689b40
- permissions
- -rw-r--r--
Implement a real Private Browsing Mode condition by changing the API/ABI;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.
1 /*
2 * Copyright (c) 2013 The WebM project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
11 #include "vp9/common/vp9_common.h"
12 #include "vp9/common/vp9_entropy.h"
14 #include "vp9/encoder/vp9_boolhuff.h"
15 #include "vp9/encoder/vp9_treewriter.h"
17 #define vp9_cost_upd ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)) >> 8)
18 #define vp9_cost_upd256 ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)))
20 static int update_bits[255];
22 static int count_uniform(int v, int n) {
23 int l = get_unsigned_bits(n);
24 int m;
25 if (l == 0) return 0;
26 m = (1 << l) - n;
27 if (v < m)
28 return l - 1;
29 else
30 return l;
31 }
33 static int split_index(int i, int n, int modulus) {
34 int max1 = (n - 1 - modulus / 2) / modulus + 1;
35 if (i % modulus == modulus / 2)
36 i = i / modulus;
37 else
38 i = max1 + i - (i + modulus - modulus / 2) / modulus;
39 return i;
40 }
42 static int recenter_nonneg(int v, int m) {
43 if (v > (m << 1))
44 return v;
45 else if (v >= m)
46 return ((v - m) << 1);
47 else
48 return ((m - v) << 1) - 1;
49 }
51 static int remap_prob(int v, int m) {
52 int i;
53 static const int map_table[MAX_PROB - 1] = {
54 // generated by:
55 // map_table[j] = split_index(j, MAX_PROB - 1, MODULUS_PARAM);
56 20, 21, 22, 23, 24, 25, 0, 26, 27, 28, 29, 30, 31, 32, 33,
57 34, 35, 36, 37, 1, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
58 48, 49, 2, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,
59 3, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 4, 74,
60 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 5, 86, 87, 88,
61 89, 90, 91, 92, 93, 94, 95, 96, 97, 6, 98, 99, 100, 101, 102,
62 103, 104, 105, 106, 107, 108, 109, 7, 110, 111, 112, 113, 114, 115, 116,
63 117, 118, 119, 120, 121, 8, 122, 123, 124, 125, 126, 127, 128, 129, 130,
64 131, 132, 133, 9, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144,
65 145, 10, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 11,
66 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 12, 170, 171,
67 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 13, 182, 183, 184, 185,
68 186, 187, 188, 189, 190, 191, 192, 193, 14, 194, 195, 196, 197, 198, 199,
69 200, 201, 202, 203, 204, 205, 15, 206, 207, 208, 209, 210, 211, 212, 213,
70 214, 215, 216, 217, 16, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227,
71 228, 229, 17, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241,
72 18, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 19,
73 };
74 v--;
75 m--;
76 if ((m << 1) <= MAX_PROB)
77 i = recenter_nonneg(v, m) - 1;
78 else
79 i = recenter_nonneg(MAX_PROB - 1 - v, MAX_PROB - 1 - m) - 1;
81 i = map_table[i];
82 return i;
83 }
85 static int count_term_subexp(int word, int k, int num_syms) {
86 int count = 0;
87 int i = 0;
88 int mk = 0;
89 while (1) {
90 int b = (i ? k + i - 1 : k);
91 int a = (1 << b);
92 if (num_syms <= mk + 3 * a) {
93 count += count_uniform(word - mk, num_syms - mk);
94 break;
95 } else {
96 int t = (word >= mk + a);
97 count++;
98 if (t) {
99 i = i + 1;
100 mk += a;
101 } else {
102 count += b;
103 break;
104 }
105 }
106 }
107 return count;
108 }
110 static int prob_diff_update_cost(vp9_prob newp, vp9_prob oldp) {
111 int delp = remap_prob(newp, oldp);
112 return update_bits[delp] * 256;
113 }
115 static void encode_uniform(vp9_writer *w, int v, int n) {
116 int l = get_unsigned_bits(n);
117 int m;
118 if (l == 0)
119 return;
120 m = (1 << l) - n;
121 if (v < m) {
122 vp9_write_literal(w, v, l - 1);
123 } else {
124 vp9_write_literal(w, m + ((v - m) >> 1), l - 1);
125 vp9_write_literal(w, (v - m) & 1, 1);
126 }
127 }
129 static void encode_term_subexp(vp9_writer *w, int word, int k, int num_syms) {
130 int i = 0;
131 int mk = 0;
132 while (1) {
133 int b = (i ? k + i - 1 : k);
134 int a = (1 << b);
135 if (num_syms <= mk + 3 * a) {
136 encode_uniform(w, word - mk, num_syms - mk);
137 break;
138 } else {
139 int t = (word >= mk + a);
140 vp9_write_literal(w, t, 1);
141 if (t) {
142 i = i + 1;
143 mk += a;
144 } else {
145 vp9_write_literal(w, word - mk, b);
146 break;
147 }
148 }
149 }
150 }
152 void vp9_write_prob_diff_update(vp9_writer *w, vp9_prob newp, vp9_prob oldp) {
153 const int delp = remap_prob(newp, oldp);
154 encode_term_subexp(w, delp, SUBEXP_PARAM, 255);
155 }
157 void vp9_compute_update_table() {
158 int i;
159 for (i = 0; i < 254; i++)
160 update_bits[i] = count_term_subexp(i, SUBEXP_PARAM, 255);
161 }
163 int vp9_prob_diff_update_savings_search(const unsigned int *ct,
164 vp9_prob oldp, vp9_prob *bestp,
165 vp9_prob upd) {
166 const int old_b = cost_branch256(ct, oldp);
167 int bestsavings = 0;
168 vp9_prob newp, bestnewp = oldp;
169 const int step = *bestp > oldp ? -1 : 1;
171 for (newp = *bestp; newp != oldp; newp += step) {
172 const int new_b = cost_branch256(ct, newp);
173 const int update_b = prob_diff_update_cost(newp, oldp) + vp9_cost_upd256;
174 const int savings = old_b - new_b - update_b;
175 if (savings > bestsavings) {
176 bestsavings = savings;
177 bestnewp = newp;
178 }
179 }
180 *bestp = bestnewp;
181 return bestsavings;
182 }
184 int vp9_prob_diff_update_savings_search_model(const unsigned int *ct,
185 const vp9_prob *oldp,
186 vp9_prob *bestp,
187 vp9_prob upd,
188 int b, int r) {
189 int i, old_b, new_b, update_b, savings, bestsavings, step;
190 int newp;
191 vp9_prob bestnewp, newplist[ENTROPY_NODES], oldplist[ENTROPY_NODES];
192 vp9_model_to_full_probs(oldp, oldplist);
193 vpx_memcpy(newplist, oldp, sizeof(vp9_prob) * UNCONSTRAINED_NODES);
194 for (i = UNCONSTRAINED_NODES, old_b = 0; i < ENTROPY_NODES; ++i)
195 old_b += cost_branch256(ct + 2 * i, oldplist[i]);
196 old_b += cost_branch256(ct + 2 * PIVOT_NODE, oldplist[PIVOT_NODE]);
198 bestsavings = 0;
199 bestnewp = oldp[PIVOT_NODE];
201 step = (*bestp > oldp[PIVOT_NODE] ? -1 : 1);
203 for (newp = *bestp; newp != oldp[PIVOT_NODE]; newp += step) {
204 if (newp < 1 || newp > 255)
205 continue;
206 newplist[PIVOT_NODE] = newp;
207 vp9_model_to_full_probs(newplist, newplist);
208 for (i = UNCONSTRAINED_NODES, new_b = 0; i < ENTROPY_NODES; ++i)
209 new_b += cost_branch256(ct + 2 * i, newplist[i]);
210 new_b += cost_branch256(ct + 2 * PIVOT_NODE, newplist[PIVOT_NODE]);
211 update_b = prob_diff_update_cost(newp, oldp[PIVOT_NODE]) +
212 vp9_cost_upd256;
213 savings = old_b - new_b - update_b;
214 if (savings > bestsavings) {
215 bestsavings = savings;
216 bestnewp = newp;
217 }
218 }
219 *bestp = bestnewp;
220 return bestsavings;
221 }
223 void vp9_cond_prob_diff_update(vp9_writer *w, vp9_prob *oldp,
224 const unsigned int ct[2]) {
225 const vp9_prob upd = DIFF_UPDATE_PROB;
226 vp9_prob newp = get_binary_prob(ct[0], ct[1]);
227 const int savings = vp9_prob_diff_update_savings_search(ct, *oldp, &newp,
228 upd);
229 assert(newp >= 1);
230 if (savings > 0) {
231 vp9_write(w, 1, upd);
232 vp9_write_prob_diff_update(w, newp, *oldp);
233 *oldp = newp;
234 } else {
235 vp9_write(w, 0, upd);
236 }
237 }
