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From: Emma Worley <emma@emma.gg>
To: ffmpeg-devel@ffmpeg.org
Date: Tue, 22 Apr 2025 00:42:52 -0700
Message-ID: <20250422074254.77328-1-emma@emma.gg>
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Subject: [FFmpeg-devel] [PATCH v4 1/3] lavc/hashtable: create generic robin
hood hash table
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Adds a generic hash table with the DXV encoder as an initial use case.
Signed-off-by: Emma Worley <emma@emma.gg>
---
libavcodec/Makefile | 2 +
libavcodec/hashtable.c | 192 +++++++++++++++++++++++++++++++++++
libavcodec/hashtable.h | 91 +++++++++++++++++
libavcodec/tests/hashtable.c | 110 ++++++++++++++++++++
4 files changed, 395 insertions(+)
create mode 100644 libavcodec/hashtable.c
create mode 100644 libavcodec/hashtable.h
create mode 100644 libavcodec/tests/hashtable.c
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index 7bd1dbec9a..8071c59378 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -42,6 +42,7 @@ OBJS = ac3_parser.o \
dv_profile.o \
encode.o \
get_buffer.o \
+ hashtable.o \
imgconvert.o \
jni.o \
lcevcdec.o \
@@ -1321,6 +1322,7 @@ TESTPROGS = avcodec \
bitstream_le \
celp_math \
codec_desc \
+ hashtable \
htmlsubtitles \
jpeg2000dwt \
mathops \
diff --git a/libavcodec/hashtable.c b/libavcodec/hashtable.c
new file mode 100644
index 0000000000..4d6d4a9506
--- /dev/null
+++ b/libavcodec/hashtable.c
@@ -0,0 +1,192 @@
+/*
+ * Generic hashtable
+ * Copyright (C) 2024 Connor Worley <connorbworley@gmail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "libavutil/crc.h"
+#include "libavutil/error.h"
+#include "libavutil/mem.h"
+#include "hashtable.h"
+
+#define ALIGN _Alignof(size_t)
+
+struct FFHashtableContext {
+ size_t key_size;
+ size_t key_size_aligned;
+ size_t val_size;
+ size_t val_size_aligned;
+ size_t entry_size;
+ size_t max_entries;
+ size_t utilization;
+ const AVCRC *crc;
+ uint8_t *table;
+ uint8_t *swapbuf;
+};
+
+#define ENTRY_PSL(entry) (entry)
+#define ENTRY_OCC(entry) (ENTRY_PSL(entry) + FFALIGN(sizeof(size_t), ALIGN))
+#define ENTRY_KEY(entry) (ENTRY_OCC(entry) + FFALIGN(sizeof(size_t), ALIGN))
+#define ENTRY_VAL(entry) (ENTRY_KEY(entry) + ctx->key_size_aligned)
+
+#define KEYS_EQUAL(k1, k2) !memcmp(k1, k2, ctx->key_size)
+
+int ff_hashtable_alloc(struct FFHashtableContext **ctx, size_t key_size, size_t val_size, size_t max_entries)
+{
+ struct FFHashtableContext *res = av_malloc(sizeof(struct FFHashtableContext));
+ if (!res)
+ return AVERROR(ENOMEM);
+ res->key_size = key_size;
+ res->key_size_aligned = FFALIGN(key_size, ALIGN);
+ res->val_size = val_size;
+ res->val_size_aligned = FFALIGN(val_size, ALIGN);
+ res->entry_size = FFALIGN(sizeof(size_t), ALIGN)
+ + FFALIGN(sizeof(size_t), ALIGN)
+ + res->key_size_aligned
+ + res->val_size_aligned;
+ res->max_entries = max_entries;
+ res->utilization = 0;
+ res->crc = av_crc_get_table(AV_CRC_32_IEEE);
+ if (!res->crc) {
+ ff_hashtable_freep(&res);
+ return AVERROR_BUG;
+ }
+ res->table = av_calloc(res->max_entries, res->entry_size);
+ if (!res->table) {
+ ff_hashtable_freep(&res);
+ return AVERROR(ENOMEM);
+ }
+ res->swapbuf = av_calloc(2, res->key_size_aligned + res->val_size_aligned);
+ if (!res->swapbuf) {
+ ff_hashtable_freep(&res);
+ return AVERROR(ENOMEM);
+ }
+ *ctx = res;
+ return 0;
+}
+
+static size_t hash_key(const struct FFHashtableContext *ctx, const void *key)
+{
+ return av_crc(ctx->crc, 0, key, ctx->key_size) % ctx->max_entries;
+}
+
+int ff_hashtable_get(const struct FFHashtableContext *ctx, const void *key, void *val)
+{
+ size_t hash = hash_key(ctx, key);
+
+ if (!ctx->utilization)
+ return 0;
+
+ for (size_t psl = 0; psl < ctx->max_entries; psl++) {
+ size_t wrapped_index = (hash + psl) % ctx->max_entries;
+ uint8_t *entry = ctx->table + wrapped_index * ctx->entry_size;
+ if (!*ENTRY_OCC(entry) || *(size_t*)ENTRY_PSL(entry) < psl)
+ return 0;
+ if (KEYS_EQUAL(ENTRY_KEY(entry), key)) {
+ memcpy(val, ENTRY_VAL(entry), ctx->val_size);
+ return 1;
+ }
+ }
+ return 0;
+}
+
+int ff_hashtable_set(struct FFHashtableContext *ctx, const void *key, const void *val)
+{
+ int swapping = 0;
+ size_t psl = 0;
+ size_t hash = hash_key(ctx, key);
+ uint8_t *set = ctx->swapbuf;
+ uint8_t *tmp = ctx->swapbuf + ctx->key_size_aligned + ctx->val_size_aligned;
+
+ memcpy(set, key, ctx->key_size);
+ memcpy(set + ctx->key_size_aligned, val, ctx->val_size);
+
+ for (size_t i = 0; i < ctx->max_entries; i++) {
+ size_t wrapped_index = (hash + i) % ctx->max_entries;
+ uint8_t *entry = ctx->table + wrapped_index * ctx->entry_size;
+ if (!*ENTRY_OCC(entry) || (!swapping && KEYS_EQUAL(ENTRY_KEY(entry), set))) {
+ if (!*ENTRY_OCC(entry))
+ ctx->utilization++;
+ *(size_t*)ENTRY_PSL(entry) = psl;
+ *ENTRY_OCC(entry) = 1;
+ memcpy(ENTRY_KEY(entry), set, ctx->key_size_aligned + ctx->val_size);
+ return 1;
+ }
+ if (*(size_t*)ENTRY_PSL(entry) < psl) {
+ if (ctx->utilization == ctx->max_entries)
+ return 0;
+ swapping = 1;
+ // set needs to swap with entry
+ memcpy(tmp, ENTRY_KEY(entry), ctx->key_size_aligned + ctx->val_size);
+ memcpy(ENTRY_KEY(entry), set, ctx->key_size_aligned + ctx->val_size);
+ FFSWAP(uint8_t*, set, tmp);
+ FFSWAP(size_t, psl, *(size_t*)ENTRY_PSL(entry));
+ }
+ psl++;
+ }
+ return 0;
+}
+
+int ff_hashtable_delete(struct FFHashtableContext *ctx, const void *key)
+{
+ uint8_t *next_entry;
+ size_t hash = hash_key(ctx, key);
+
+ if (!ctx->utilization)
+ return 0;
+
+ for (size_t psl = 0; psl < ctx->max_entries; psl++) {
+ size_t wrapped_index = (hash + psl) % ctx->max_entries;
+ uint8_t *entry = ctx->table + wrapped_index * ctx->entry_size;
+ if (!*ENTRY_OCC(entry) || *(size_t*)ENTRY_PSL(entry) < psl)
+ return 0;
+ if (KEYS_EQUAL(ENTRY_KEY(entry), key)) {
+ *ENTRY_OCC(entry) = 0;
+ for (psl++; psl < ctx->max_entries; psl++) {
+ wrapped_index = (hash + psl) % ctx->max_entries;
+ next_entry = ctx->table + wrapped_index * ctx->entry_size;
+ if (!*ENTRY_OCC(next_entry) || !*(size_t*)ENTRY_PSL(next_entry)) {
+ ctx->utilization--;
+ return 1;
+ }
+ memcpy(entry, next_entry, ctx->entry_size);
+ (*(size_t*)ENTRY_PSL(entry))--;
+ *ENTRY_OCC(next_entry) = 0;
+ entry = next_entry;
+ }
+ }
+ };
+ return 0;
+}
+
+void ff_hashtable_clear(struct FFHashtableContext *ctx)
+{
+ memset(ctx->table, 0, ctx->entry_size * ctx->max_entries);
+}
+
+void ff_hashtable_freep(struct FFHashtableContext **ctx)
+{
+ if (*ctx) {
+ av_freep(&(*ctx)->table);
+ av_freep(&(*ctx)->swapbuf);
+ }
+ av_freep(ctx);
+}
diff --git a/libavcodec/hashtable.h b/libavcodec/hashtable.h
new file mode 100644
index 0000000000..fd28d3bdd7
--- /dev/null
+++ b/libavcodec/hashtable.h
@@ -0,0 +1,91 @@
+/*
+ * Generic hashtable
+ * Copyright (C) 2024 Connor Worley <connorbworley@gmail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_HASHTABLE_H
+#define AVCODEC_HASHTABLE_H
+
+#include <stddef.h>
+
+/* Implements a hash table using Robin Hood open addressing.
+ * See: https://cs.uwaterloo.ca/research/tr/1986/CS-86-14.pdf
+ */
+
+struct FFHashtableContext;
+
+/**
+ * Creates a fixed-sized Robin Hood hash table.
+ *
+ * @param ctx context to allocate and initialize
+ * @param key_size size of key type in bytes
+ * @param val_size size of value type in bytes
+ * @param max_entries maximum number of key-value pairs to store
+ *
+ * @return zero on success, nonzero on error
+ */
+int ff_hashtable_alloc(struct FFHashtableContext **ctx, size_t key_size, size_t val_size, size_t max_entries);
+
+/**
+ * Looks up a value from a hash table given a key.
+ *
+ * @param ctx hash table context
+ * @param key pointer to key data
+ * @param val destination pointer for value data
+ *
+ * @return 1 if the key is found, zero if the key is not found
+ */
+int ff_hashtable_get(const struct FFHashtableContext *ctx, const void *key, void *val);
+
+/**
+ * Stores a value in a hash table given a key.
+ *
+ * @param ctx hash table context
+ * @param key pointer to key data
+ * @param val pointer for value data
+ *
+ * @return 1 if the key is written, zero if the key is not written due to the hash table reaching max capacity
+ */
+int ff_hashtable_set(struct FFHashtableContext *ctx, const void *key, const void *val);
+
+/**
+ * Deletes a value from a hash table given a key.
+ *
+ * @param ctx hash table context
+ * @param key pointer to key data
+ *
+ * @return 1 if the key is deleted, zero if the key is not deleted due to not being found
+ */
+int ff_hashtable_delete(struct FFHashtableContext *ctx, const void *key);
+
+/**
+ * Deletes all values from a hash table.
+ *
+ * @param ctx hash table context
+ */
+void ff_hashtable_clear(struct FFHashtableContext *ctx);
+
+/**
+ * Frees a hash table.
+ *
+ * @param ctx hash table context
+ */
+void ff_hashtable_freep(struct FFHashtableContext **ctx);
+
+#endif
diff --git a/libavcodec/tests/hashtable.c b/libavcodec/tests/hashtable.c
new file mode 100644
index 0000000000..367baf4f96
--- /dev/null
+++ b/libavcodec/tests/hashtable.c
@@ -0,0 +1,110 @@
+/*
+ * Generic hashtable tests
+ * Copyright (C) 2024 Connor Worley <connorbworley@gmail.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdint.h>
+
+#include "libavutil/avassert.h"
+#include "libavcodec/hashtable.h"
+
+int main(void)
+{
+ struct FFHashtableContext *ctx;
+ uint8_t k;
+ uint64_t v;
+
+ // impossibly large allocation should fail gracefully
+ av_assert0(ff_hashtable_alloc(&ctx, -1, -1, -1) < 0);
+
+ // hashtable can store up to 3 uint8_t->uint64_t entries
+ av_assert0(!ff_hashtable_alloc(&ctx, sizeof(k), sizeof(v), 3));
+
+ // unsuccessful deletes return 0
+ k = 1;
+ av_assert0(!ff_hashtable_delete(ctx, &k));
+
+ // unsuccessful gets return 0
+ k = 1;
+ av_assert0(!ff_hashtable_get(ctx, &k, &v));
+
+ // successful sets returns 1
+ k = 1;
+ v = 1;
+ av_assert0(ff_hashtable_set(ctx, &k, &v));
+
+ // get should now contain 1
+ k = 1;
+ v = 0;
+ av_assert0(ff_hashtable_get(ctx, &k, &v));
+ av_assert0(v == 1);
+
+ // updating sets should return 1
+ k = 1;
+ v = 2;
+ av_assert0(ff_hashtable_set(ctx, &k, &v));
+
+ // get should now contain 2
+ k = 1;
+ v = 0;
+ av_assert0(ff_hashtable_get(ctx, &k, &v));
+ av_assert0(v == 2);
+
+ // fill the table
+ k = 2;
+ v = 2;
+ av_assert0(ff_hashtable_set(ctx, &k, &v));
+ k = 3;
+ v = 3;
+ av_assert0(ff_hashtable_set(ctx, &k, &v));
+
+ // inserting sets on a full table should return 0
+ k = 4;
+ v = 4;
+ av_assert0(!ff_hashtable_set(ctx, &k, &v));
+
+ // updating sets on a full table should return 1
+ k = 1;
+ v = 4;
+ av_assert0(ff_hashtable_set(ctx, &k, &v));
+ v = 0;
+ av_assert0(ff_hashtable_get(ctx, &k, &v));
+ av_assert0(v == 4);
+
+ // successful deletes should return 1
+ k = 1;
+ av_assert0(ff_hashtable_delete(ctx, &k));
+
+ // get should now return 0
+ av_assert0(!ff_hashtable_get(ctx, &k, &v));
+
+ // sanity check remaining keys
+ k = 2;
+ v = 0;
+ av_assert0(ff_hashtable_get(ctx, &k, &v));
+ av_assert0(v == 2);
+ k = 3;
+ v = 0;
+ av_assert0(ff_hashtable_get(ctx, &k, &v));
+ av_assert0(v == 3);
+
+ ff_hashtable_freep(&ctx);
+
+ return 0;
+}
--
2.48.0
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