[FFmpeg-devel] [PATCH v2 1/2] lavu/hashtable: create generic robin hood hash table

[Connor Worley <connorbworley@gmail.com>]

Signed-off-by: Connor Worley <connorbworley@gmail.com>
---
 libavutil/Makefile          |   2 +
 libavutil/hashtable.c       | 183 ++++++++++++++++++++++++++++++++++++
 libavutil/hashtable.h       |  47 +++++++++
 libavutil/tests/hashtable.c | 108 +++++++++++++++++++++
 4 files changed, 340 insertions(+)
 create mode 100644 libavutil/hashtable.c
 create mode 100644 libavutil/hashtable.h
 create mode 100644 libavutil/tests/hashtable.c

diff --git a/libavutil/Makefile b/libavutil/Makefile
index e7709b97d0..be75d464fc 100644
--- a/libavutil/Makefile
+++ b/libavutil/Makefile
@@ -138,6 +138,7 @@ OBJS = adler32.o                                                        \
        fixed_dsp.o                                                      \
        frame.o                                                          \
        hash.o                                                           \
+       hashtable.o                                                      \
        hdr_dynamic_metadata.o                                           \
        hdr_dynamic_vivid_metadata.o                                     \
        hmac.o                                                           \
@@ -251,6 +252,7 @@ TESTPROGS = adler32                                                     \
             file                                                        \
             fifo                                                        \
             hash                                                        \
+            hashtable                                                   \
             hmac                                                        \
             hwdevice                                                    \
             integer                                                     \
diff --git a/libavutil/hashtable.c b/libavutil/hashtable.c
new file mode 100644
index 0000000000..6fa2af8af3
--- /dev/null
+++ b/libavutil/hashtable.c
@@ -0,0 +1,183 @@
+/*
+ * 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 "crc.h"
+#include "error.h"
+#include "mem.h"
+#include "hashtable.h"
+
+struct AVHashtableContext {
+    size_t key_size;
+    size_t val_size;
+    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) + sizeof(size_t))
+#define ENTRY_KEY(entry) (ENTRY_OCC(entry) + 4)
+#define ENTRY_VAL(entry) (ENTRY_KEY(entry) + FFALIGN(ctx->key_size, 4))
+
+#define KEYS_EQUAL(k1, k2) !memcmp(k1, k2, ctx->key_size)
+
+int av_hashtable_alloc(struct AVHashtableContext** ctx, size_t key_size, size_t val_size, size_t max_entries)
+{
+    struct AVHashtableContext *res = av_malloc(sizeof(struct AVHashtableContext));
+    if (!res)
+        return AVERROR(ENOMEM);
+    res->key_size = key_size;
+    res->val_size = val_size;
+    res->entry_size = sizeof(size_t) + 4 + FFALIGN(key_size, 4) + FFALIGN(val_size, 4);
+    res->max_entries = max_entries;
+    res->utilization = 0;
+    res->crc = av_crc_get_table(AV_CRC_32_IEEE);
+    if (!res->crc) {
+        av_hashtable_freep(&res);
+        return AVERROR_BUG;
+    }
+    res->table = av_calloc(res->max_entries, res->entry_size);
+    if (!res->table) {
+        av_hashtable_freep(&res);
+        return AVERROR(ENOMEM);
+    }
+    res->swapbuf = av_calloc(2, FFALIGN(key_size, 4) + FFALIGN(val_size, 4));
+    if (!res->swapbuf) {
+        av_hashtable_freep(&res);
+        return AVERROR(ENOMEM);
+    }
+    *ctx = res;
+    return 0;
+}
+
+static size_t hash_key(const struct AVHashtableContext* ctx, const void* key)
+{
+    return av_crc(ctx->crc, 0, key, ctx->key_size) % ctx->max_entries;
+}
+
+int av_hashtable_get(const struct AVHashtableContext* 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 av_hashtable_set(struct AVHashtableContext* 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 + FFALIGN(ctx->key_size, 4) + FFALIGN(ctx->val_size, 4);
+
+    memcpy(set, key, ctx->key_size);
+    memcpy(set + FFALIGN(ctx->key_size, 4), 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, FFALIGN(ctx->key_size, 4) + 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), FFALIGN(ctx->key_size, 4) + ctx->val_size);
+            memcpy(ENTRY_KEY(entry), set, FFALIGN(ctx->key_size, 4) + ctx->val_size);
+            FFSWAP(uint8_t*, set, tmp);
+            FFSWAP(size_t, psl, *(size_t*)ENTRY_PSL(entry));
+        }
+        psl++;
+    }
+    return 0;
+}
+
+int av_hashtable_delete(struct AVHashtableContext* 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_OCC(entry), ENTRY_OCC(next_entry), ctx->entry_size);
+                *(size_t*)ENTRY_PSL(entry)--;
+                *ENTRY_OCC(next_entry) = 0;
+                entry = next_entry;
+            }
+        }
+    };
+    return 0;
+}
+
+void av_hashtable_clear(struct AVHashtableContext* ctx)
+{
+    memset(ctx->table, 0, ctx->entry_size * ctx->max_entries);
+}
+
+void av_hashtable_freep(struct AVHashtableContext** ctx)
+{
+    if (*ctx) {
+        av_freep(&(*ctx)->table);
+        av_freep(&(*ctx)->swapbuf);
+    }
+    av_freep(ctx);
+}
diff --git a/libavutil/hashtable.h b/libavutil/hashtable.h
new file mode 100644
index 0000000000..90c6cad68a
--- /dev/null
+++ b/libavutil/hashtable.h
@@ -0,0 +1,47 @@
+/*
+ * 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 AVUTIL_HASHTABLE_H
+#define AVUTIL_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
+ *
+ * Entry slots are layed out in memory as follows:
+ * - [1 byte] occupancy flag that indicates whether a slot if occupied.
+ * - [key_size bytes] entry key.
+ * - [val_size bytes] entry value.
+ * - [sizeof(size_t) bytes] PSL (probe sequence length), used by the Robin Hood
+ *   algorithm.
+ */
+
+struct AVHashtableContext;
+
+int av_hashtable_alloc(struct AVHashtableContext** ctx, size_t key_size, size_t val_size, size_t max_entries);
+int av_hashtable_get(const struct AVHashtableContext* ctx, const void* key, void* val);
+int av_hashtable_set(struct AVHashtableContext* ctx, const void* key, const void* val);
+int av_hashtable_delete(struct AVHashtableContext* ctx, const void* key);
+void av_hashtable_clear(struct AVHashtableContext* ctx);
+void av_hashtable_freep(struct AVHashtableContext** ctx);
+
+#endif
diff --git a/libavutil/tests/hashtable.c b/libavutil/tests/hashtable.c
new file mode 100644
index 0000000000..0b38b34c5c
--- /dev/null
+++ b/libavutil/tests/hashtable.c
@@ -0,0 +1,108 @@
+/*
+ * 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 "libavutil/avassert.h"
+#include "libavutil/hashtable.h"
+
+int main(void)
+{
+    struct AVHashtableContext *ctx;
+    uint8_t k;
+    uint64_t v;
+
+    // impossibly large allocation should fail gracefully
+    av_assert0(av_hashtable_alloc(&ctx, -1, -1, -1) < 0);
+
+    // hashtable can store up to 3 uint8_t->uint64_t entries
+    av_assert0(!av_hashtable_alloc(&ctx, sizeof(k), sizeof(v), 3));
+
+    // unsuccessful deletes return 0
+    k = 1;
+    av_assert0(!av_hashtable_delete(ctx, &k));
+
+    // unsuccessful gets return 0
+    k = 1;
+    av_assert0(!av_hashtable_get(ctx, &k, &v));
+
+    // successful sets returns 1
+    k = 1;
+    v = 1;
+    av_assert0(av_hashtable_set(ctx, &k, &v));
+
+    // get should now contain 1
+    k = 1;
+    v = 0;
+    av_assert0(av_hashtable_get(ctx, &k, &v));
+    av_assert0(v == 1);
+
+    // updating sets should return 1
+    k = 1;
+    v = 2;
+    av_assert0(av_hashtable_set(ctx, &k, &v));
+
+    // get should now contain 2
+    k = 1;
+    v = 0;
+    av_assert0(av_hashtable_get(ctx, &k, &v));
+    av_assert0(v == 2);
+
+    // fill the table
+    k = 2;
+    v = 2;
+    av_assert0(av_hashtable_set(ctx, &k, &v));
+    k = 3;
+    v = 3;
+    av_assert0(av_hashtable_set(ctx, &k, &v));
+
+    // inserting sets on a full table should return 0
+    k = 4;
+    v = 4;
+    av_assert0(!av_hashtable_set(ctx, &k, &v));
+
+    // updating sets on a full table should return 1
+    k = 1;
+    v = 4;
+    av_assert0(av_hashtable_set(ctx, &k, &v));
+    v = 0;
+    av_assert0(av_hashtable_get(ctx, &k, &v));
+    av_assert0(v == 4);
+
+    // successful deletes should return 1
+    k = 1;
+    av_assert0(av_hashtable_delete(ctx, &k));
+
+    // get should now return 0
+    av_assert0(!av_hashtable_get(ctx, &k, &v));
+
+    // sanity check remaining keys
+    k = 2;
+    v = 0;
+    av_assert0(av_hashtable_get(ctx, &k, &v));
+    av_assert0(v == 2);
+    k = 3;
+    v = 0;
+    av_assert0(av_hashtable_get(ctx, &k, &v));
+    av_assert0(v == 3);
+
+    av_hashtable_freep(&ctx);
+
+    return 0;
+}
-- 
2.40.1

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