commit b13e0f09c12809f6799c1615194932c7638d7510
Author: seajee <teapods@proton.me>
Date:   Tue Nov 18 21:33:06 2025 +0100

    Initial commit

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..1cc8e11
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,6 @@
+
+test: main.c hm.h
+	cc -Wall -Wextra -ggdb -o test main.c
+
+clean:
+	rm -rf test
diff --git a/hm.h b/hm.h
new file mode 100644
index 0000000..47cdc01
--- /dev/null
+++ b/hm.h
@@ -0,0 +1,544 @@
+// hm.h - v1.0.0 - MIT License
+// chained hash table implementation as a single header library.
+
+#ifndef _HM_H_
+#define _HM_H_
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#ifndef HM_INITIAL_CAPACITY
+#    define HM_INITIAL_CAPACITY 256
+#endif // HM_INITIAL_CAPACITY
+
+#ifndef HM_MAX_LOAD_FACTOR
+#    define HM_MAX_LOAD_FACTOR 0.75f
+#endif // HM_MAX_LOAD_FACTOR
+
+#ifndef HM_GROWTH_FACTOR
+#    define HM_GROWTH_FACTOR 2
+#endif // HM_GROWTH_FACTOR
+
+#ifndef HM_NO_ASSERT
+#    ifndef HM_ASSERT
+#        include <assert.h>
+#        define HM_ASSERT assert
+#    endif // HM_ASSERT
+#else
+#    define HM_ASSERT(...) ((void)0)
+#endif // HM_NO_ASSERT
+
+#ifndef HM_REALLOC
+#    include <stdlib.h>
+#    define HM_REALLOC realloc
+#endif // HM_REALLOC
+
+#ifndef HM_FREE
+#    include <stdlib.h>
+#    define HM_FREE free
+#endif // HM_FREE
+
+#ifdef __cplusplus
+extern "C" { // Prevent name mangling
+#endif // __cplusplus
+
+typedef struct Hm__Bucket {
+    struct Hm__Bucket *next;
+    struct Hm__Bucket *prev;
+    void *key;
+    void *value;
+    size_t value_size;
+} Hm__Bucket;
+
+typedef struct {
+    Hm__Bucket **map;
+    size_t count;
+    size_t capacity;
+    size_t key_size;
+    size_t value_size;
+} HashMap;
+
+typedef struct {
+    const HashMap *hm;
+    Hm__Bucket *bucket;
+    size_t index;
+    bool end;
+} HashMapIterator;
+
+// Create and free
+HashMap hm_create(size_t key_size, size_t value_size);
+void hm_free(HashMap *hm);
+
+// Modify, access and remove
+bool hm_put(HashMap *hm, const void *key, const void *value);
+void *hm_get(const HashMap *hm, const void *key);
+bool hm_remove(HashMap *hm, const void *key);
+
+// Iterator functions
+HashMapIterator hm_iterate(const HashMap *hm);
+const void *hm_key(const HashMapIterator *it);
+void *hm_value(const HashMapIterator *it);
+void *hm_next(HashMapIterator *it);
+
+// Private functions
+uint64_t hm__fnv1a(const void *buffer, size_t size);
+size_t hm__key_size(const HashMap *hm, const void *key);
+size_t hm__value_size(const HashMap *hm, const void *value);
+bool hm__keycmp(const HashMap *hm, const void *key1, const void *key2);
+bool hm__rehash(HashMap *hm);
+Hm__Bucket *hm__bucket_create(const void *key, size_t key_size, const void *value, size_t value_size);
+
+#ifdef __cplusplus
+}
+#endif // __cplusplus
+
+#endif // _HM_H_
+
+#ifdef HM_IMPLEMENTATION
+
+#ifdef __cplusplus
+extern "C" { // Prevent name mangling
+#endif // __cplusplus
+
+HashMap hm_create(size_t key_size, size_t value_size)
+{
+    HashMap hm;
+    memset(&hm, 0, sizeof(hm));
+    hm.capacity = HM_INITIAL_CAPACITY;
+    hm.key_size = key_size;
+    hm.value_size = value_size;
+    return hm;
+}
+
+void hm_free(HashMap *hm)
+{
+    if (hm == NULL || hm->map == NULL) {
+        memset(hm, 0, sizeof(*hm));
+        return;
+    }
+
+    for (size_t i = 0; i < hm->capacity; ++i) {
+        Hm__Bucket *cur = hm->map[i];
+        if (cur == NULL) {
+            continue;
+        }
+
+        while (cur != NULL) {
+            Hm__Bucket *next = cur->next;
+            HM_FREE(cur->key);
+            HM_FREE(cur->value);
+            HM_FREE(cur);
+            cur = next;
+        }
+    }
+
+    HM_FREE(hm->map);
+    memset(hm, 0, sizeof(*hm));
+}
+
+bool hm_put(HashMap *hm, const void *key, const void *value)
+{
+    if (hm == NULL || key == NULL || value == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return false;
+    }
+
+    // Ensure that HashMap is initialised
+    if (hm->map == NULL) {
+        hm->map = (Hm__Bucket**)HM_REALLOC(NULL, sizeof(*hm->map) * HM_INITIAL_CAPACITY);
+        if (hm->map == NULL) {
+            HM_ASSERT(false && "Reallocation failed");
+            return false;
+        }
+        hm->capacity = HM_INITIAL_CAPACITY;
+        memset(hm->map, 0, sizeof(*hm->map) * hm->capacity);
+    }
+
+    // Rehash if necessary
+    if ((float)hm->count + 1 > (float)hm->capacity * HM_MAX_LOAD_FACTOR) {
+        if (!hm__rehash(hm)) {
+            return false;
+        }
+    }
+
+    // Key-value sizes
+    size_t key_size = hm__key_size(hm, key);
+    size_t value_size = hm__value_size(hm, value);
+
+    // Get the head bucket
+    size_t idx = hm__fnv1a(key, key_size) % hm->capacity;
+    Hm__Bucket *head = hm->map[idx];
+
+    // Check if key already exists
+    for (Hm__Bucket *cur = head; cur != NULL; cur = cur->next) {
+        if (!hm__keycmp(hm, key, cur->key)) {
+            continue;
+        }
+
+        // Fixed or equal value_size
+        if (hm->value_size != 0 || value_size == cur->value_size) {
+            memcpy(cur->value, value, value_size);
+            return true;
+        }
+
+        // Temporary buffer in case of overlapping pointers
+        uint8_t *tmp = (uint8_t*)HM_REALLOC(NULL, value_size);
+        if (tmp == NULL) {
+            HM_ASSERT(false && "Reallocation failed");
+            return false;
+        }
+        memcpy(tmp, value, value_size);
+
+        // Realloc and copy
+        uint8_t *new_value = (uint8_t*)HM_REALLOC(cur->value, value_size);
+        if (new_value == NULL) {
+            HM_ASSERT(false && "Reallocation failed");
+            return false;
+        }
+        cur->value = new_value;
+        memcpy(cur->value, tmp, value_size);
+
+        HM_FREE(tmp);
+
+        return true;
+    }
+
+    // Insert the new value
+    Hm__Bucket *new_bucket = hm__bucket_create(key, key_size, value, value_size);
+    if (new_bucket == NULL) {
+        return false;
+    }
+
+    new_bucket->next = head;
+    if (head != NULL) {
+        head->prev = new_bucket;
+    }
+    hm->map[idx] = new_bucket;
+    ++hm->count;
+
+    return true;
+}
+
+void *hm_get(const HashMap *hm, const void *key)
+{
+    if (hm == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return NULL;
+    }
+
+    if (hm->map == NULL || key == NULL) {
+        return NULL;
+    }
+
+    size_t key_size = hm__key_size(hm, key);
+    size_t idx = hm__fnv1a(key, key_size) % hm->capacity;
+
+    Hm__Bucket *head = hm->map[idx];
+    if (head == NULL) {
+        return NULL;
+    }
+
+    for (Hm__Bucket *cur = head; cur != NULL; cur = cur->next) {
+        if (hm__keycmp(hm, key, cur->key)) {
+            return cur->value;
+        }
+    }
+
+    return NULL;
+}
+
+bool hm_remove(HashMap *hm, const void *key)
+{
+    if (hm == NULL || hm->map == NULL || key == NULL) {
+        return false;
+    }
+
+    size_t key_size = hm__key_size(hm, key);
+    size_t idx = hm__fnv1a(key, key_size) % hm->capacity;
+
+    Hm__Bucket *head = hm->map[idx];
+    if (head == NULL) {
+        return false;
+    }
+
+    for (Hm__Bucket *cur = head; cur != NULL; cur = cur->next) {
+        if (hm__keycmp(hm, key, cur->key)) {
+            if (cur == head) {
+                hm->map[idx] = cur->next;
+            } else {
+                cur->prev->next = cur->next;
+            }
+
+            if (cur->next != NULL) {
+                cur->next->prev = cur->prev;
+            }
+
+            HM_FREE(cur->key);
+            HM_FREE(cur->value);
+            HM_FREE(cur);
+            --hm->count;
+            return true;
+        }
+    }
+
+    return false;
+}
+
+HashMapIterator hm_iterate(const HashMap *hm)
+{
+    HashMapIterator it;
+    memset(&it, 0, sizeof(it));
+
+    if (hm == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+    }
+
+    it.hm = hm;
+
+    return it;
+}
+
+const void *hm_key(const HashMapIterator *it)
+{
+    if (it == NULL || it->hm == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return NULL;
+    }
+
+    // Reached the end
+    if (it->end) {
+        return NULL;
+    }
+
+    return it->bucket->key;
+}
+
+void *hm_value(const HashMapIterator *it)
+{
+    if (it == NULL || it->hm == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return NULL;
+    }
+
+    // Reached the end
+    if (it->end) {
+        return NULL;
+    }
+
+    return it->bucket->value;
+}
+
+void *hm_next(HashMapIterator *it)
+{
+    if (it == NULL || it->hm == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return NULL;
+    }
+
+    // Reached the end
+    if (it->end) {
+        return NULL;
+    }
+
+    if (it->bucket == NULL) {
+        // Find first list of buckets
+        while ((it->bucket = it->hm->map[it->index++]) == NULL);
+        return it->bucket->value;
+    }
+
+    // Next bucket
+    if (it->bucket->next != NULL) {
+        it->bucket = it->bucket->next;
+        return it->bucket->value;
+    }
+
+    // Find next list of buckets
+    while ((it->bucket = it->hm->map[++it->index]) == NULL);
+
+    // Reached the end
+    if (it->index >= it->hm->capacity) {
+        it->end = true;
+        return NULL;
+    }
+
+    it->bucket = it->hm->map[it->index];
+    return it->bucket->value;
+}
+
+uint64_t hm__fnv1a(const void *buffer, size_t size)
+{
+    if (buffer == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return 0;
+    }
+
+    const uint8_t *b = (const uint8_t*)buffer;
+    uint64_t hash = 14695981039346656037ULL;
+
+    for (size_t i = 0; i < size; ++i) {
+        hash ^= b[i];
+        hash *= 1099511628211ULL;
+    }
+
+    return hash;
+}
+
+size_t hm__key_size(const HashMap *hm, const void *key)
+{
+    if (hm == NULL || key == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return 0;
+    }
+
+    return (hm->key_size == 0 ? strlen((const char*)key) + 1 : hm->key_size);
+}
+
+size_t hm__value_size(const HashMap *hm, const void *value)
+{
+    if (hm == NULL || value == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return 0;
+    }
+
+    return (hm->value_size == 0 ? strlen((const char*)value) + 1 : hm->value_size);
+}
+
+bool hm__keycmp(const HashMap *hm, const void *key1, const void *key2)
+{
+    if (hm == NULL || key1 == NULL || key2 == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return false;
+    }
+
+    if (hm->key_size == 0) {
+        return strcmp((const char*)key1, (const char*)key2) == 0;
+    }
+
+    return memcmp(key1, key2, hm->key_size) == 0;
+}
+
+bool hm__rehash(HashMap *hm)
+{
+    if (hm == NULL || hm->map == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return false;
+    }
+
+    // Allocate new table
+    size_t new_capacity = hm->capacity * HM_GROWTH_FACTOR;
+    Hm__Bucket **new_map = (Hm__Bucket**)HM_REALLOC(NULL, sizeof(*new_map) * new_capacity);
+    if (new_map == NULL) {
+        HM_ASSERT(false && "Reallocation failed");
+        return false;
+    }
+    memset(new_map, 0, sizeof(*new_map) * new_capacity);
+
+    // Iterate old table
+    for (size_t i = 0; i < hm->capacity; ++i) {
+        Hm__Bucket *cur = hm->map[i];
+        while (cur != NULL) {
+            Hm__Bucket *next = cur->next;
+
+            size_t key_size = hm__key_size(hm, cur->key);
+            uint64_t idx = hm__fnv1a(cur->key, key_size) % new_capacity;
+
+            // Insert new bucket
+            cur->prev = NULL;
+            cur->next = new_map[idx];
+            if (new_map[idx] != NULL) {
+                new_map[idx]->prev = cur;
+            }
+            new_map[idx] = cur;
+
+            cur = next;
+        }
+    }
+
+    HM_FREE(hm->map);
+    hm->map = new_map;
+    hm->capacity = new_capacity;
+
+    return true;
+}
+
+Hm__Bucket *hm__bucket_create(const void *key, size_t key_size, const void *value, size_t value_size)
+{
+    if (key == NULL || value == NULL) {
+        HM_ASSERT(false && "Invalid parameters");
+        return NULL;
+    }
+
+    // Allocate bucket
+    Hm__Bucket *bucket = (Hm__Bucket*)HM_REALLOC(NULL, sizeof(*bucket));
+    if (bucket == NULL) {
+        HM_ASSERT(false && "Reallocation failed");
+        return NULL;
+    }
+    memset(bucket, 0, sizeof(*bucket));
+
+    // Allocate key
+    bucket->key = HM_REALLOC(NULL, key_size);
+    if (bucket->key == NULL) {
+        HM_ASSERT(false && "Reallocation failed");
+        HM_FREE(bucket);
+        return NULL;
+    }
+    memset(bucket->key, 0, key_size);
+
+    // Allocate value
+    bucket->value = HM_REALLOC(NULL, value_size);
+    if (bucket->value == NULL) {
+        HM_ASSERT(false && "Reallocation failed");
+        HM_FREE(bucket->key);
+        HM_FREE(bucket);
+        return NULL;
+    }
+    memset(bucket->value, 0, value_size);
+
+    // Copy Key-value data
+    memcpy(bucket->key, key, key_size);
+    memcpy(bucket->value, value, value_size);
+    bucket->value_size = value_size;
+
+    return bucket;
+}
+
+#ifdef __cplusplus
+}
+#endif // __cplusplus
+
+#endif // HM_IMPLEMENTATION
+
+// TODO: Find a way to reduce calls to malloc
+
+/*
+ * Revision history:
+ *
+ *     1.0.0 (2025-11-18) Initial release
+ */
+
+/*
+ * MIT License
+ *
+ * Copyright (c) 2025 seajee
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..7f87a18
--- /dev/null
+++ b/main.c
@@ -0,0 +1,58 @@
+#include <stdio.h>
+
+#define HM_IMPLEMENTATION
+#define HM_INITIAL_CAPACITY 1
+#include "hm.h"
+
+void print_hm(const HashMap *hm)
+{
+    HashMapIterator it = hm_iterate(hm);
+    while (hm_next(&it) != NULL) {
+        printf("%-15s: ", (const char*)hm_key(&it));
+        printf("%d\n", *(int*)hm_value(&it));
+    }
+}
+
+const char *words[49] = {
+    "apple", "banana", "cherry", "date", "elderberry", "fig", "grape",
+    "honeydew", "apple", "banana", "kiwi", "lemon", "mango", "nectarine",
+    "orange", "papaya", "quince", "raspberry", "strawberry", "tangerine",
+    "ugli", "voavanga", "watermelon", "xigua", "yellowfruit", "zucchini",
+    "apple", "banana", "cherry", "mango", "kiwi", "lemon", "lemon", "orange",
+    "papaya", "papaya", "grape", "grape", "grape", "strawberry", "strawberry",
+    "date", "date", "date", "fig", "fig", "elderberry", "nectarine", "plum"
+};
+const size_t N = sizeof(words)/sizeof(words[0]);
+const int ONE = 1;
+
+int main(void)
+{
+    HashMap freq = hm_create(0, sizeof(int));
+
+    for (size_t i = 0; i < N; ++i) {
+        const char *word = words[i];
+
+        int *f = hm_get(&freq, word);
+        if (f == NULL) {
+            hm_put(&freq, word, &ONE);
+        } else {
+            *f += 1;
+        }
+    }
+
+    print(&freq);
+    printf("count = %zu\n", freq.count);
+
+    HashMapIterator it = hm_iterate(&freq);
+    hm_next(&it);
+    while (hm_value(&it) != NULL) {
+        const void *key = hm_key(&it);
+        hm_next(&it);
+        hm_remove(&freq, key);
+    }
+
+    printf("count = %zu\n", freq.count);
+    hm_free(&freq);
+
+    return 0;
+}