feat and refactor: Added mult_size_t_safe and changed how new capacity is calculated for an arena

I wanted to separate things but i was getting confused on how exactly to do it
so i did the best i could, just multiply everithing by 2 and if it overflows then
well, return error, should be enough for most cases to be honest

.gitignore

@@ -52,3 +52,5 @@ rules.ninja
 *.swo
 *~
 
+# Git
+COMMIT_MESSAGE

include/arena.h

@@ -1,4 +1,62 @@
 #ifndef ARENA_H
 #define ARENA_H
 
+#include <stdint.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <stdbool.h>
+
+typedef struct {
+    uint8_t *buffer;
+    size_t capacity;
+    size_t offset;
+} Arena;
+
+typedef enum {
+    ARENA_OK = 0,
+    ARENA_BAD_ALLOC,
+    ARENA_OUT_OF_SPACE,
+    ARENA_NULL_ARG,
+    ARENA_INVALID_SIZE,
+    ARENA_INVALID_ALIGN,
+    ARENA_CAPACITY_OVERFLOW,
+} ArenaErr;
+
+typedef struct {
+    bool is_valid;
+    union {
+        ArenaErr err;
+        uint8_t *address;
+    };
+} ArenaPointer;
+
+typedef struct {
+    bool is_valid;
+    union {
+        ArenaErr err;
+        Arena arena;
+    };
+} ArenaResult;
+
+typedef struct {
+    bool is_valid;
+    union {
+        ArenaErr err;
+        size_t val;
+    };
+} SizeResult;
+
+ArenaResult arena_init(size_t capacity);
+void arena_destroy(Arena *arena);
+
+ArenaPointer arena_alloc(Arena *arena, size_t size, size_t alignment);
+ArenaErr arena_push(Arena *arena, void *data, size_t size, size_t alignment);
+ArenaErr arena_realloc(Arena *arena, size_t new_capacity);
+
+SizeResult align_arena_offset(Arena *arena, size_t alignment);
+
+// Should be moved to something like general utilities,
+// i should make one for all my c projects
+bool mul_size_t_safe(size_t a, size_t b, size_t *out);
+
 #endif // !ARENA_H

src/arena.c

@@ -1 +1,172 @@
 #include "arena.h"
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+ArenaResult arena_init(size_t capacity) {
+
+    void *buffer = malloc(capacity);
+    if (buffer == NULL) {
+        ArenaResult err = {
+            .is_valid = false,
+            .err = ARENA_BAD_ALLOC,
+        };
+        return err;
+    }
+
+    if (capacity < 1) {
+        ArenaResult err = {
+            .is_valid = false,
+            .err = ARENA_INVALID_SIZE,
+        };
+        return err;
+    }
+
+    Arena new_arena = {
+        .buffer = buffer,
+        .capacity = capacity,
+        .offset = 0,
+    };
+    ArenaResult val = {
+        .is_valid = true,
+        .arena = new_arena,
+    };
+
+    return val;
+}
+
+void arena_destroy(Arena *arena) {
+    if (arena == NULL) {
+        return;
+    }
+
+    arena->offset = 0;
+    arena->capacity = 0;
+    free(arena->buffer);
+}
+
+ArenaPointer arena_alloc(Arena *arena, size_t size, size_t alignment) {
+    if (arena == NULL) {
+        ArenaPointer err = {
+            .is_valid = false,
+            .err = ARENA_NULL_ARG,
+        };
+        return err;
+    }
+
+    SizeResult new_offset = align_arena_offset(arena, alignment);
+    if (!new_offset.is_valid) {
+        ArenaPointer err = {
+            .is_valid = false,
+            .err = new_offset.err,
+        };
+        return err;
+    }
+
+    if (new_offset.val + size >= arena->capacity) {
+        ArenaPointer err = {
+            .is_valid = false,
+            .err = ARENA_OUT_OF_SPACE,
+        };
+        return err;
+    }
+
+    arena->offset = new_offset.val;
+
+    ArenaPointer val = {
+        .is_valid = true,
+        .address = arena->buffer + arena->offset,
+    };
+    return val;
+}
+
+ArenaErr arena_push(Arena *arena, void *data, size_t size, size_t alignment) {
+    if (arena == NULL || data == NULL) {
+        return ARENA_NULL_ARG;
+    }
+
+    ArenaPointer pointer = arena_alloc(arena, size, alignment);
+
+    if (!pointer.is_valid) {
+        return pointer.err;
+    }
+    while (!pointer.is_valid && pointer.err == ARENA_OUT_OF_SPACE) {
+        size_t new_capacity;
+
+        bool is_overflow = mul_size_t_safe(arena->capacity, 2, &new_capacity);
+        if (is_overflow) {
+            return ARENA_CAPACITY_OVERFLOW;
+        }
+
+        ArenaErr err = arena_realloc(arena, new_capacity);
+        if (err != ARENA_OK) {
+            return err;
+        }
+
+        pointer = arena_alloc(arena, size, alignment);
+    }
+
+    memcpy(
+        pointer.address,
+        data,
+        size);
+
+    return ARENA_OK;
+}
+
+ArenaErr arena_realloc(Arena *arena, size_t new_capacity) {
+    if (arena == NULL) {
+        return ARENA_NULL_ARG;
+    }
+
+    uint8_t *tmp = realloc(arena->buffer, new_capacity);
+    if (tmp == NULL) {
+        return ARENA_BAD_ALLOC;
+    }
+
+    arena->buffer = tmp;
+    arena->capacity = new_capacity;
+    return ARENA_OK;
+}
+
+SizeResult align_arena_offset(Arena *arena, size_t alignment) {
+    if (arena == NULL) {
+        SizeResult err = {
+            .is_valid = false,
+            .err = ARENA_NULL_ARG,
+        };
+        return err;
+    }
+
+    if (alignment < 1) {
+        SizeResult err = {
+            .is_valid = false,
+            .err = ARENA_INVALID_ALIGN,
+        };
+        return err;
+    }
+
+    SizeResult val = {
+        .is_valid = true,
+        .val = ((arena->offset + (alignment - 1)) & ~(alignment - 1)),
+        // Formula for alignment, found at stackoverflow, i came up with one
+        // but it involved 3 divisions, this one is way faster :)
+    };
+    return val;
+}
+
+bool mul_size_t_safe(size_t a, size_t b, size_t *out) {
+    if (out == NULL) {
+        return true;
+    }
+
+    if (a != 0 && b > SIZE_MAX / a) {
+        return true;
+    }
+
+    *out = a * b;
+    return false;
+}
+