FFmpeg coverage

Directory: ../../../ffmpeg/
File: src/libavcodec/hashtable.c
Date: 2025-06-05 01:40:37
Exec Total Coverage
Lines: 89 99 89.9%
Functions: 7 7 100.0%
Branches: 39 52 75.0%
Line Branch Exec Source
1 /*
2 * Generic hashtable
3 * Copyright (C) 2025 Emma Worley <emma@emma.gg>
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22 #include <stdint.h>
23 #include <string.h>
24
25 #include "libavutil/attributes.h"
26 #include "libavutil/crc.h"
27 #include "libavutil/error.h"
28 #include "libavutil/macros.h"
29 #include "libavutil/mem.h"
30 #include "hashtable.h"
31
32 #define ALIGN _Alignof(size_t)
33
34 struct FFHashtableContext {
35 size_t key_size;
36 size_t val_size;
37 size_t entry_size;
38 size_t max_entries;
39 size_t nb_entries;
40 const AVCRC *crc;
41 uint8_t *table;
42 uint8_t swapbuf[];
43 };
44
45 /*
46 * Hash table entries are comprised of a probe sequence length (PSL), key, and
47 * value. When the PSL of an entry is zero, it means it is not occupied by a
48 * key/value pair. When the PSL is non-zero, it represents the "distance" of
49 * the entry from its "home" location plus one, where the "home" location is
50 * hash(key) % max_entries.
51 */
52
53 #define ENTRY_PSL_VAL(entry) (*(size_t*)(entry))
54 #define ENTRY_KEY_PTR(entry) ((entry) + sizeof(size_t))
55 #define ENTRY_VAL_PTR(entry) (ENTRY_KEY_PTR(entry) + ctx->key_size)
56
57 #define KEYS_EQUAL(k1, k2) (!memcmp((k1), (k2), ctx->key_size))
58
59 29 av_cold int ff_hashtable_alloc(FFHashtableContext **ctx, size_t key_size,
60 size_t val_size, size_t max_entries)
61 {
62 29 const size_t keyval_size = key_size + val_size;
63
64
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 29 if (keyval_size < key_size || // did (unsigned,defined) wraparound happen?
65 keyval_size > FFMIN(SIZE_MAX - sizeof(size_t) - (ALIGN - 1),
66 (SIZE_MAX - sizeof(FFHashtableContext)) / 2))
67 1 return AVERROR(ERANGE);
68
69 28 FFHashtableContext *res = av_mallocz(sizeof(*res) + 2 * keyval_size);
70
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 28 if (!res)
71 ✗ return AVERROR(ENOMEM);
72 28 res->key_size = key_size;
73 28 res->val_size = val_size;
74 28 res->entry_size = FFALIGN(sizeof(size_t) + keyval_size, ALIGN);
75 28 res->max_entries = max_entries;
76 28 res->nb_entries = 0;
77 28 res->crc = av_crc_get_table(AV_CRC_32_IEEE);
78
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 28 if (!res->crc) {
79 ✗ ff_hashtable_freep(&res);
80 ✗ return AVERROR_BUG;
81 }
82 28 res->table = av_calloc(res->max_entries, res->entry_size);
83
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 28 if (!res->table) {
84 ✗ ff_hashtable_freep(&res);
85 ✗ return AVERROR(ENOMEM);
86 }
87
88 28 *ctx = res;
89 28 return 0;
90 }
91
92 731034 static size_t hash_key(const struct FFHashtableContext *ctx, const void *key)
93 {
94 731034 return av_crc(ctx->crc, 0, key, ctx->key_size) % ctx->max_entries;
95 }
96
97 337209 int ff_hashtable_get(const struct FFHashtableContext *ctx, const void *key, void *val)
98 {
99
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 337209 if (!ctx->nb_entries)
100 1 return 0;
101
102 337208 size_t hash = hash_key(ctx, key);
103
104
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 337436 for (size_t psl = 1; psl <= ctx->max_entries; psl++) {
105 337436 size_t wrapped_index = (hash + psl) % ctx->max_entries;
106 337436 uint8_t *entry = ctx->table + wrapped_index * ctx->entry_size;
107
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 337436 if (ENTRY_PSL_VAL(entry) < psl)
108 // When PSL stops increasing it means there are no further entries
109 // with the same key hash.
110 12054 return 0;
111
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 325382 if (KEYS_EQUAL(ENTRY_KEY_PTR(entry), key)) {
112 325154 memcpy(val, ENTRY_VAL_PTR(entry), ctx->val_size);
113 325154 return 1;
114 }
115 }
116 ✗ return 0;
117 }
118
119 391686 int ff_hashtable_set(struct FFHashtableContext *ctx, const void *key, const void *val)
120 {
121 391686 int swapping = 0;
122 391686 size_t psl = 1;
123 391686 size_t hash = hash_key(ctx, key);
124 391686 size_t wrapped_index = hash % ctx->max_entries;
125 391686 uint8_t *set = ctx->swapbuf;
126 391686 uint8_t *tmp = ctx->swapbuf + ctx->key_size + ctx->val_size;
127
128 391686 memcpy(set, key, ctx->key_size);
129 391686 memcpy(set + ctx->key_size, val, ctx->val_size);
130
131
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 391919 for (size_t i = 0; i < ctx->max_entries; i++) {
132
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 391919 if (++wrapped_index == ctx->max_entries)
133 3 wrapped_index = 0;
134 391919 uint8_t *entry = ctx->table + wrapped_index * ctx->entry_size;
135
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 391919 if (!ENTRY_PSL_VAL(entry) || (!swapping && KEYS_EQUAL(ENTRY_KEY_PTR(entry), set))) {
136
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 391685 if (!ENTRY_PSL_VAL(entry))
137 12059 ctx->nb_entries++;
138 391685 ENTRY_PSL_VAL(entry) = psl;
139 391685 memcpy(ENTRY_KEY_PTR(entry), set, ctx->key_size + ctx->val_size);
140 391685 return 1;
141 }
142
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 234 if (ENTRY_PSL_VAL(entry) < psl) {
143 // When PSL stops increasing it means there are no further entries
144 // with the same key hash. We can only hope to find an unoccupied
145 // entry.
146
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 3 if (ctx->nb_entries == ctx->max_entries)
147 // The table is full so inserts are impossible.
148 1 return 0;
149 // Robin Hood hash tables "steal from the rich" by minimizing the
150 // PSL of the inserted entry.
151 2 swapping = 1;
152 // set needs to swap with entry
153 2 memcpy(tmp, ENTRY_KEY_PTR(entry), ctx->key_size + ctx->val_size);
154 2 memcpy(ENTRY_KEY_PTR(entry), set, ctx->key_size + ctx->val_size);
155 2 FFSWAP(uint8_t*, set, tmp);
156 2 FFSWAP(size_t, psl, ENTRY_PSL_VAL(entry));
157 }
158 233 psl++;
159 }
160 ✗ return 0;
161 }
162
163 2141 int ff_hashtable_delete(struct FFHashtableContext *ctx, const void *key)
164 {
165
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 2141 if (!ctx->nb_entries)
166 1 return 0;
167
168 uint8_t *next_entry;
169 2140 size_t hash = hash_key(ctx, key);
170 2140 size_t wrapped_index = hash % ctx->max_entries;
171
172
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 2140 for (size_t psl = 1; psl <= ctx->max_entries; psl++) {
173
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 2140 if (++wrapped_index == ctx->max_entries)
174 ✗ wrapped_index = 0;
175 2140 uint8_t *entry = ctx->table + wrapped_index * ctx->entry_size;
176
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 2140 if (ENTRY_PSL_VAL(entry) < psl)
177 // When PSL stops increasing it means there are no further entries
178 // with the same key hash.
179 ✗ return 0;
180
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 2140 if (KEYS_EQUAL(ENTRY_KEY_PTR(entry), key)) {
181 2140 ENTRY_PSL_VAL(entry) = 0;
182 // Shift each following entry that will benefit from a reduced PSL.
183
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 2182 for (psl++; psl <= ctx->max_entries; psl++) {
184
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 2182 if (++wrapped_index == ctx->max_entries)
185 1 wrapped_index = 0;
186 2182 next_entry = ctx->table + wrapped_index * ctx->entry_size;
187
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 2182 if (ENTRY_PSL_VAL(next_entry) <= 1) {
188 2140 ctx->nb_entries--;
189 2140 return 1;
190 }
191 42 memcpy(entry, next_entry, ctx->entry_size);
192 42 ENTRY_PSL_VAL(entry)--;
193 42 ENTRY_PSL_VAL(next_entry) = 0;
194 42 entry = next_entry;
195 }
196 }
197 }
198 ✗ return 0;
199 }
200
201 3 void ff_hashtable_clear(struct FFHashtableContext *ctx)
202 {
203 3 memset(ctx->table, 0, ctx->entry_size * ctx->max_entries);
204 3 }
205
206 28 av_cold void ff_hashtable_freep(FFHashtableContext **ctx)
207 {
208
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 28 if (*ctx) {
209 28 av_freep(&(*ctx)->table);
210 28 av_freep(ctx);
211 }
212 28 }
213