Initial commit

LICENSE

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+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.

Makefile

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+
+test: test.c arena.h
+	cc -Wall -Wextra -DDEBUG -o test test.c
+
+clean:
+	rm -rf test

README.md

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+# arena.h
+
+A single header library that implements
+[https://en.wikipedia.org/wiki/Region-based_memory_management](region-based memory management) in C.
+
+## Example
+
+```c
+#define ARENA_IMPLEMENTATION
+#include "arena.h"
+
+int main(void)
+{
+    Arena a = {0};
+
+    int *x = arena_alloc(&a, sizeof(*x) * 69);
+    float *y = arena_alloc(&a, sizeof(*y) * 420);
+
+    arena_free(&a);
+    return 0;
+}
+```

arena.h

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+#ifndef ARENA_H_
+#define ARENA_H_
+
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifndef ARENA_MIN_CAPACITY
+#define ARENA_MIN_CAPACITY 4096
+#endif // ARENA_MIN_CAPACITY
+
+typedef struct Arena_Region Arena_Region;
+
+struct Arena_Region {
+    size_t count;
+    size_t capacity;
+    Arena_Region *next;
+    uint8_t data[];
+};
+
+typedef struct {
+    Arena_Region *head;
+    Arena_Region *tail;
+} Arena;
+
+void *arena_alloc(Arena *a, size_t bytes);
+void arena_free(Arena *a);
+void arena_reset(Arena *a);
+
+#endif // ARENA_H_
+
+#ifdef ARENA_IMPLEMENTATION
+
+void *arena_alloc(Arena *a, size_t bytes)
+{
+    if (a == NULL) {
+        return NULL;
+    }
+
+    // Empty a
+    if (a->head == NULL) {
+        size_t size = (bytes > ARENA_MIN_CAPACITY ? bytes : ARENA_MIN_CAPACITY);
+        a->head = malloc(sizeof(*a->head) + size);
+        if (a->head == NULL) {
+            return NULL;
+        }
+        memset(a->head, 0, sizeof(*a->head));
+        a->head->count = bytes;
+        a->head->capacity = size;
+        a->tail = a->head;
+        return a->head->data;
+    }
+
+    // Not enough capacity
+    if (bytes > a->tail->capacity - a->tail->count) {
+        // Find first suitable region
+        while (a->tail->next != NULL && bytes > a->tail->capacity - a->tail->count) {
+            a->tail = a->tail->next;
+        }
+
+        // If found allocate on that region
+        if (bytes <= a->tail->capacity - a->tail->count) {
+            a->tail->count += bytes;
+            return a->tail->data + a->tail->count;
+        }
+
+        // If not create a new region
+        a->tail->next = malloc(sizeof(*a->tail) + bytes);
+        if (a->tail->next == NULL) {
+            return NULL;
+        }
+        a->tail = a->tail->next;
+        memset(a->tail, 0, sizeof(*a->tail));
+        a->tail->count = bytes;
+        a->tail->capacity = bytes;
+        return a->tail->data;
+    }
+
+    a->tail->count += bytes;
+    return a->tail->data + a->tail->count;
+}
+
+void arena_free(Arena *a)
+{
+    if (a == NULL) {
+        return;
+    }
+
+    Arena_Region *cur = a->head;
+    while (cur != NULL) {
+        Arena_Region *next = cur->next;
+        free(cur);
+        cur = next;
+    }
+
+    memset(a, 0, sizeof(*a));
+}
+
+void arena_reset(Arena *a)
+{
+    if (a == NULL) {
+        return;
+    }
+
+    for (Arena_Region *cur = a->head; cur != NULL; cur = cur->next) {
+        cur->count = 0;
+    }
+
+    a->tail = a->head;
+}
+
+#endif // ARENA_IMPLEMENTATION

test.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+#ifdef DEBUG
+#define malloc(n) (printf("%s:%d:%s: malloc(%ld)\n",\
+            __FILE__, __LINE__, __func__, (n)), malloc((n)));
+#define free(p)   (printf("%s:%d:%s: free(%p)\n",\
+            __FILE__, __LINE__, __func__, (p)), free((p)));
+#endif // DEBUG
+
+#define ARENA_MIN_CAPACITY 400
+#define ARENA_IMPLEMENTATION
+#include "arena.h"
+
+void arena_print(Arena arena)
+{
+    int i = 0;
+    for (Arena_Region *cur = arena.head; cur != NULL; cur = cur->next) {
+        printf("Arena_Region #%d:\n", ++i);
+        printf("    count    = %ld\n", cur->count);
+        printf("    capacity = %ld\n", cur->capacity);
+        printf("    next     = %p\n", cur->next);
+        printf("    data     = %p\n", cur->data);
+    }
+}
+
+int main(void)
+{
+    Arena a = {0};
+
+    printf("------ small alloc ------\n");
+
+    arena_alloc(&a, 100);
+    arena_alloc(&a, 100);
+    arena_alloc(&a, 100);
+    arena_alloc(&a, 100);
+    arena_print(a);
+
+    printf("\n=========================================================\n\n");
+    printf("------ big alloc ------\n");
+
+    arena_alloc(&a, 8000);
+    arena_print(a);
+
+    printf("\n=========================================================\n\n");
+    printf("------ reset ------\n");
+
+    arena_reset(&a);
+    arena_print(a);
+
+    printf("\n=========================================================\n\n");
+    printf("------ allocs after reset ------\n");
+
+    arena_alloc(&a, 300);
+    arena_alloc(&a, 400);
+    arena_alloc(&a, 9000);
+    arena_print(a);
+
+    arena_free(&a);
+    return 0;
+}