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+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+/**
+ * @file vec.h
+ * @brief A dynamically sized contiguous sequence with byte-based storage.
+ *
+ * `struct vec` stores the element size rather than a type. The caller is
+ * responsible for using the type associated with the initialized element size.
+ */
+#ifndef VEC_H
+#define VEC_H
+
+#include <stddef.h>
+#include <stdbool.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+/**
+ * @brief A dynamically sized contiguous sequence.
+ *
+ * `data` points to storage for at most `capacity` elements. The first
+ * `size` positions contain valid elements.
+ */
+typedef struct vec {
+ void *data;
+ size_t size;
+ size_t capacity;
+ size_t elem_size;
+} vec;
+
+/**
+ * @brief Compares two elements.
+ *
+ * @return A value less than, equal to, or greater than zero when the left
+ * element is less than, equal to, or greater than the right element.
+ */
+typedef int (*vec_compare_fn)(const void *lhs, const void *rhs);
+
+/** @name Initialization */
+/** @{ */
+
+/**
+ * @brief Produces an initializer for an empty vector of the given element type.
+ * @param type The element type.
+ */
+#define VEC_INIT(type) { \
+ .data = NULL, \
+ .size = 0, \
+ .capacity = 0, \
+ .elem_size = sizeof(type), \
+}
+
+/**
+ * @brief Declares and initializes a vector for the given element type.
+ * @param name The vector variable name.
+ * @param type The element type.
+ */
+#define VEC(name, type) \
+ struct vec name = VEC_INIT(type)
+
+/**
+ * @brief Initializes an existing vector.
+ * @param v A pointer to the vector.
+ * @param type The element type.
+ */
+#define vec_init(v, type) \
+ (*(v) = (struct vec)VEC_INIT(type))
+
+/** @} */
+
+/** @name Basic properties */
+/** @{ */
+
+/** @brief Returns the number of valid elements in the vector. */
+static inline size_t vec_size(const struct vec *v)
+{
+ return v->size;
+}
+
+/** @brief Returns the current storage capacity of the vector. */
+static inline size_t vec_capacity(const struct vec *v)
+{
+ return v->capacity;
+}
+
+/** @brief Returns the size of one element in bytes. */
+static inline size_t vec_elem_size(const struct vec *v)
+{
+ return v->elem_size;
+}
+
+/**
+ * @brief Returns the maximum number of elements representable at this element size.
+ */
+static inline size_t vec_max_size(const struct vec *v)
+{
+ return SIZE_MAX / v->elem_size;
+}
+
+/** @brief Tests whether the vector is empty. */
+static inline int vec_empty(const struct vec *v)
+{
+ return v->size == 0;
+}
+
+/** @} */
+
+/** @name Lifetime and capacity */
+/** @{ */
+
+/**
+ * @brief Removes all valid elements from the vector.
+ *
+ * The operation does not release the allocated capacity.
+ */
+static inline void vec_clear(struct vec *v)
+{
+ v->size = 0;
+}
+
+/**
+ * @brief Destroys the vector and releases its storage.
+ */
+static inline void vec_destroy(struct vec *v)
+{
+ free(v->data);
+
+ v->data = NULL;
+ v->size = 0;
+ v->capacity = 0;
+ v->elem_size = 0;
+}
+
+/**
+ * @brief Ensures that the vector has at least the requested capacity.
+ * @param v A pointer to the vector.
+ * @param capacity The minimum requested number of elements.
+ * @return `true` on success; `false` on overflow or allocation failure.
+ */
+static inline bool vec_reserve(struct vec *v, size_t capacity)
+{
+ if (!v || v->elem_size == 0) {
+ return false;
+ }
+ // 当前容量已满足需求，直接返回成功
+ if (capacity <= v->capacity) {
+ return true;
+ }
+ // 乘法溢出检查 (capacity * elem_size > SIZE_MAX)
+ if (capacity > SIZE_MAX / v->elem_size) {
+ return false;
+ }
+
+ size_t new_bytes = capacity * v->elem_size;
+ void *new_data = realloc(v->data, new_bytes);
+ if (!new_data) {
+ return false; // 分配失败，原 v->data 依然有效
+ }
+
+ v->data = new_data;
+ v->capacity = capacity;
+ return true;
+}
+
+/**
+ * @brief Changes the number of valid elements in the vector.
+ *
+ * Elements added by growing the vector are uninitialized.
+ *
+ * @param v A pointer to the vector.
+ * @param size The new number of elements.
+ * @return `true` on success; `false` on allocation failure.
+ */
+static inline bool vec_resize(struct vec *v, size_t size)
+{
+ if (!v) {
+ return false;
+ }
+
+ if (size > v->capacity) {
+ if (!vec_reserve(v, size)) {
+ return false;
+ }
+ }
+ v->size = size;
+ return true;
+}
+
+/**
+ * @brief Changes the vector size and clears newly added bytes.
+ *
+ * Clearing bytes does not guarantee a type-specific zero value; it only
+ * guarantees that the corresponding storage bytes are zero.
+ */
+static inline bool vec_resize_zero(struct vec *v, size_t size)
+{
+ if (!v) {
+ return false;
+ }
+ size_t old_size = v->size;
+
+ if (size > old_size) {
+ if (size > v->capacity) {
+ if (!vec_reserve(v, size)) {
+ return false;
+ }
+ }
+ /* 这里使用 memset 清零字节，不保证所有元素类型都得到
+ * 该类型语义上的零值。 */
+ char *start = (char *)v->data + (old_size * v->elem_size);
+ size_t zero_bytes = (size - old_size) * v->elem_size;
+ memset(start, 0, zero_bytes);
+ }
+
+ v->size = size;
+ return true;
+}
+
+/**
+ * @brief Attempts to reduce the capacity to the current size.
+ * @return `true` on success; `false` if reallocation fails.
+ */
+static inline bool vec_shrink_to_fit(struct vec *v)
+{
+ if (!v || v->elem_size == 0) {
+ return false;
+ }
+ // 已经完全贴合，无需缩容
+ if (v->capacity == v->size) {
+ return true;
+ }
+
+ // 当 size == 0 时，彻底归还堆内存
+ if (v->size == 0) {
+ free(v->data);
+ v->data = NULL;
+ v->capacity = 0;
+ return true;
+ }
+
+ // 缩容至刚好容纳 size 个元素
+ size_t bytes = v->size * v->elem_size;
+ void *new_data = realloc(v->data, bytes);
+ if (!new_data) {
+ return false; // 极少数情况下缩容可能失败，保持原样
+ }
+
+ v->data = new_data;
+ v->capacity = v->size;
+ return true;
+}
+
+/** @} */
+
+/** @name Raw element access */
+/** @{ */
+
+/** @brief Returns a writable pointer to the vector storage. */
+static inline void *vec_data(struct vec *v)
+{
+ return v->data;
+}
+
+/** @brief Returns a read-only pointer to the vector storage. */
+static inline const void *vec_data_const(const struct vec *v)
+{
+ return v->data;
+}
+
+/**
+ * @brief Tests two vectors for equality using a comparison function.
+ */
+static inline bool vec_equal(const struct vec *a,
+ const struct vec *b,
+ vec_compare_fn compare)
+{
+ if (a->elem_size != b->elem_size || a->size != b->size) {
+ return false;
+ }
+
+ for (size_t i = 0; i < a->size; ++i) {
+ const void *lhs = (const unsigned char *)a->data
+ + i * a->elem_size;
+ const void *rhs = (const unsigned char *)b->data
+ + i * b->elem_size;
+ if (compare(lhs, rhs) != 0) {
+ return false;
+ }
+ }
+ return true;
+}
+
+/**
+ * @brief Compares two vectors lexicographically.
+ * @return -1, 0, or 1 when the left vector is less than, equal to, or
+ * greater than the right vector.
+ */
+static inline int vec_compare(const struct vec *a,
+ const struct vec *b,
+ vec_compare_fn compare)
+{
+ size_t common_size = a->size < b->size ? a->size : b->size;
+
+ for (size_t i = 0; i < common_size; ++i) {
+ const void *lhs = (const unsigned char *)a->data
+ + i * a->elem_size;
+ const void *rhs = (const unsigned char *)b->data
+ + i * b->elem_size;
+ int result = compare(lhs, rhs);
+ if (result < 0) {
+ return -1;
+ }
+ if (result > 0) {
+ return 1;
+ }
+ }
+
+ if (a->size < b->size) {
+ return -1;
+ }
+ if (a->size > b->size) {
+ return 1;
+ }
+ return 0;
+}
+
+/**
+ * @brief Returns a writable pointer to the element at `index`.
+ * @pre `index < v->size`.
+ */
+static inline void *vec_at(struct vec *v, size_t index)
+{
+ assert(index < v->size);
+
+ return (unsigned char *)v->data
+ + index * v->elem_size;
+}
+
+/**
+ * @brief Returns a read-only pointer to the element at `index`.
+ * @pre `index < v->size`.
+ */
+static inline const void *vec_at_const(const struct vec *v,
+ size_t index)
+{
+ assert(index < v->size);
+
+ return (const unsigned char *)v->data
+ + index * v->elem_size;
+}
+
+/**
+ * @brief Returns a writable pointer to the element at `index`, or `NULL`
+ * when `index` is out of range.
+ */
+static inline void *vec_at_checked(struct vec *v, size_t index)
+{
+ if (index >= v->size) {
+ return NULL;
+ }
+
+ return (unsigned char *)v->data
+ + index * v->elem_size;
+}
+
+/**
+ * @brief Returns a read-only pointer to the element at `index`, or `NULL`
+ * when `index` is out of range.
+ */
+static inline const void *vec_at_checked_const(const struct vec *v,
+ size_t index)
+{
+ if (index >= v->size) {
+ return NULL;
+ }
+
+ return (const unsigned char *)v->data
+ + index * v->elem_size;
+}
+
+/**
+ * @brief Returns a writable pointer to the first element.
+ * @pre The vector is not empty.
+ */
+static inline void *vec_front(struct vec *v)
+{
+ assert(v->size);
+ return v->data;
+}
+
+/**
+ * @brief Returns a read-only pointer to the first element.
+ * @pre The vector is not empty.
+ */
+static inline const void *vec_front_const(const struct vec *v)
+{
+ assert(v->size);
+ return v->data;
+}
+
+/**
+ * @brief Returns a writable pointer to the last element.
+ * @pre The vector is not empty.
+ */
+static inline void *vec_back(struct vec *v)
+{
+ assert(v->size);
+ return vec_at(v, v->size - 1);
+}
+
+/**
+ * @brief Returns a read-only pointer to the last element.
+ * @pre The vector is not empty.
+ */
+static inline const void *vec_back_const(const struct vec *v)
+{
+ assert(v->size);
+ return vec_at_const(v, v->size - 1);
+}
+
+/** @} */
+
+/** @name Typed access macros */
+/** @{ */
+
+/** @brief Converts the storage pointer to a writable pointer of `type`. */
+#define vec_data_as(v, type) \
+ ((type *)vec_data(v))
+
+/** @brief Converts the storage pointer to a read-only pointer of `type`. */
+#define vec_data_as_const(v, type) \
+ ((const type *)vec_data_const(v))
+
+/** @brief Accesses the writable element at `i` as `type`. */
+#define vec_at_as(v, type, i) \
+ (*(type *)vec_at((v), (i)))
+
+/** @brief Accesses the read-only element at `i` as `type`. */
+#define vec_at_as_const(v, type, i) \
+ (*(const type *)vec_at_const((v), (i)))
+
+/** @brief Accesses the first element as a writable `type`. */
+#define vec_front_as(v, type) \
+ (*(type *)vec_front(v))
+
+/** @brief Accesses the first element as a read-only `type`. */
+#define vec_front_as_const(v, type) \
+ (*(const type *)vec_front_const(v))
+
+/** @brief Accesses the last element as a writable `type`. */
+#define vec_back_as(v, type) \
+ (*(type *)vec_back(v))
+
+/** @brief Accesses the last element as a read-only `type`. */
+#define vec_back_as_const(v, type) \
+ (*(const type *)vec_back_const(v))
+
+/** @} */
+
+/** @name Raw element insertion */
+/** @{ */
+
+/* 内部辅助函数：按 2 倍几何级数扩容，确保至少容纳 needed 个元素 */
+static inline bool __vec_grow_to(struct vec *v, size_t needed)
+{
+ size_t max_elements = SIZE_MAX / v->elem_size;
+ if (needed > max_elements) {
+ return false;
+ }
+ if (needed <= v->capacity) {
+ return true;
+ }
+ // 初始默认给 8 个元素容量，之后每次翻倍
+ size_t new_cap = v->capacity ? v->capacity : 8;
+ if (new_cap > max_elements) {
+ new_cap = max_elements;
+ }
+ while (new_cap < needed) {
+ // 防止翻倍超过最大元素数量
+ if (new_cap > max_elements / 2) {
+ new_cap = max_elements;
+ break;
+ }
+ new_cap *= 2;
+ }
+ return vec_reserve(v, new_cap);
+}
+
+/**
+ * @brief Reserves an uninitialized slot at the end of the vector.
+ * @return A pointer to the new slot, or `NULL` on failure.
+ */
+static inline void *vec_emplace_back(struct vec *v)
+{
+ if (!v || v->elem_size == 0) {
+ return NULL;
+ }
+ size_t max_elements = SIZE_MAX / v->elem_size;
+ if (v->size >= max_elements) {
+ return NULL;
+ }
+ size_t needed = v->size + 1;
+ /* Grow the storage when the current capacity is exhausted. */
+ if (v->size >= v->capacity) {
+ if (!__vec_grow_to(v, needed)) {
+ return NULL;
+ }
+ }
+ void *slot = (char *)v->data + (v->size * v->elem_size);
+ v->size++;
+ return slot;
+}
+
+static inline size_t __vec_source_index(const struct vec *v,
+ const void *elem)
+{
+ if (!v || !v->data || !elem || v->elem_size == 0) {
+ return SIZE_MAX;
+ }
+
+ uintptr_t base = (uintptr_t)v->data;
+ uintptr_t address = (uintptr_t)elem;
+ if (address < base) {
+ return SIZE_MAX;
+ }
+
+ uintptr_t offset = address - base;
+ if (offset % v->elem_size != 0) {
+ return SIZE_MAX;
+ }
+
+ size_t index = (size_t)(offset / v->elem_size);
+ return index < v->size ? index : SIZE_MAX;
+}
+
+/**
+ * @brief Appends one raw element to the vector.
+ * @param v A pointer to the vector.
+ * @param elem A pointer to the element to copy.
+ * @return `true` on success; `false` on invalid input or allocation failure.
+ */
+static inline bool vec_push_back(struct vec *v,
+ const void *elem)
+{
+ if (!elem) {
+ return false;
+ }
+ size_t source_index = __vec_source_index(v, elem);
+ void *slot = vec_emplace_back(v);
+ if (!slot) {
+ return false;
+ }
+ const void *source = source_index == SIZE_MAX
+ ? elem
+ : (const unsigned char *)v->data
+ + source_index * v->elem_size;
+ memcpy(slot, source, v->elem_size);
+ return true;
+}
+
+/**
+ * @brief Reserves an uninitialized slot at `index`.
+ * @param v A pointer to the vector.
+ * @param index The insertion index in the range `[0, size]`.
+ * @return A pointer to the new slot, or `NULL` on failure.
+ */
+static inline void *vec_emplace(struct vec *v,
+ size_t index)
+{
+ if (!v || v->elem_size == 0 || index > v->size) {
+ return NULL;
+ }
+ size_t max_elements = SIZE_MAX / v->elem_size;
+ if (v->size >= max_elements) {
+ return NULL;
+ }
+ size_t needed = v->size + 1;
+ if (v->size >= v->capacity) {
+ if (!__vec_grow_to(v, needed)) {
+ return NULL;
+ }
+ }
+ char *slot = (char *)v->data + (index * v->elem_size);
+
+ /* Shift the suffix when insertion is not at the end. */
+ if (index < v->size) {
+ memmove(slot + v->elem_size, slot, (v->size - index) * v->elem_size);
+ }
+
+ v->size++;
+ return (void *)slot;
+
+}
+
+/**
+ * @brief Inserts one raw element at `index`.
+ * @param v A pointer to the vector.
+ * @param index The insertion index in the range `[0, size]`.
+ * @param elem A pointer to the element to copy.
+ * @return `true` on success; `false` on invalid input or allocation failure.
+ */
+static inline bool vec_insert(struct vec *v,
+ size_t index,
+ const void *elem)
+{
+ if (!elem) {
+ return false;
+ }
+ size_t source_index = __vec_source_index(v, elem);
+ void *slot = vec_emplace(v, index);
+ if (!slot) {
+ return false;
+ }
+ if (source_index != SIZE_MAX && source_index >= index) {
+ source_index++;
+ }
+ const void *source = source_index == SIZE_MAX
+ ? elem
+ : (const unsigned char *)v->data
+ + source_index * v->elem_size;
+ memcpy(slot, source, v->elem_size);
+ return true;
+}
+
+/**
+ * @brief Inserts a range of raw elements at `index`.
+ *
+ * The source range must not refer to the vector's storage.
+ *
+ * @param v A pointer to the vector.
+ * @param index The insertion index in the range `[0, size]`.
+ * @param src The source range.
+ * @param count The number of elements to insert.
+ * @return `true` on success; `false` on invalid input or allocation failure.
+ */
+static inline bool vec_insert_range(struct vec *v,
+ size_t index,
+ const void *src,
+ size_t count)
+{
+ /* 前置条件：src 不得指向当前 vector 的存储区，
+ * 这与 std::vector::insert(position, first, last) 一致。 */
+ if (!v || v->elem_size == 0 || index > v->size) {
+ return false;
+ }
+ if (count == 0) {
+ return true; /* Inserting zero elements succeeds. */
+ }
+ if (!src) {
+ return false;
+ }
+ /* Check for overflow in size + count. */
+ if (count > SIZE_MAX - v->size) {
+ return false;
+ }
+
+ size_t needed = v->size + count;
+ if (needed > v->capacity) {
+ if (!__vec_grow_to(v, needed)) {
+ return false;
+ }
+ }
+
+ char *dest = (char *)v->data + (index * v->elem_size);
+
+ /* Shift the suffix when insertion is not at the end. */
+ if (index < v->size) {
+ memmove(dest + (count * v->elem_size), dest, (v->size - index) * v->elem_size);
+ }
+
+ /* Copy the source range into the newly opened gap. */
+ memcpy(dest, src, count * v->elem_size);
+ v->size += count;
+ return true;
+}
+
+/**
+ * @brief Replaces the vector with `count` copies of one raw element.
+ * @param v A pointer to the vector.
+ * @param count The resulting number of elements.
+ * @param value A pointer to the value to copy.
+ * @return `true` on success; `false` on invalid input or allocation failure.
+ */
+static inline bool vec_assign_n(struct vec *v,
+ size_t count,
+ const void *value)
+{
+ if (!v || v->elem_size == 0) {
+ return false;
+ }
+ if (count == 0) {
+ v->size = 0;
+ return true;
+ }
+ if (!value || count > vec_max_size(v)) {
+ return false;
+ }
+
+ size_t source_index = __vec_source_index(v, value);
+ if (count > v->capacity && !vec_reserve(v, count)) {
+ return false;
+ }
+
+ const void *source = source_index == SIZE_MAX
+ ? value
+ : (const unsigned char *)v->data
+ + source_index * v->elem_size;
+ for (size_t i = 0; i < count; ++i) {
+ void *dest = (unsigned char *)v->data + i * v->elem_size;
+ memmove(dest, source, v->elem_size);
+ }
+ v->size = count;
+ return true;
+}
+
+/**
+ * @brief Replaces the vector with a range of raw elements.
+ *
+ * The source range must not refer to the vector's storage.
+ *
+ * @param v A pointer to the vector.
+ * @param src The source range.
+ * @param count The number of elements to assign.
+ * @return `true` on success; `false` on invalid input or allocation failure.
+ */
+static inline bool vec_assign_range(struct vec *v,
+ const void *src,
+ size_t count)
+{
+ /* 前置条件：src 不得指向当前 vector 的存储区。 */
+ if (!v || v->elem_size == 0) {
+ return false;
+ }
+ if (count == 0) {
+ v->size = 0;
+ return true;
+ }
+ if (!src || count > vec_max_size(v)) {
+ return false;
+ }
+ if (count > v->capacity && !vec_reserve(v, count)) {
+ return false;
+ }
+
+ memmove(v->data, src, count * v->elem_size);
+ v->size = count;
+ return true;
+}
+
+/**
+ * @brief Appends a range of raw elements to the vector.
+ *
+ * The source range must not refer to the vector's storage.
+ *
+ * @param v A pointer to the vector.
+ * @param src The source range.
+ * @param count The number of elements to append.
+ * @return `true` on success; `false` on invalid input or allocation failure.
+ */
+static inline bool vec_append(struct vec *v,
+ const void *src,
+ size_t count)
+{
+ /* The source must not refer to the vector's storage. */
+ if (!v) {
+ return false;
+ }
+ /* Reuse vec_insert_range() at the current end position. */
+ return vec_insert_range(v, v->size, src, count);
+}
+
+
+/** @} */
+
+/** @name Value insertion wrappers */
+/** @{ */
+
+/** @brief Appends a typed value after checking its size. */
+#define vec_push(v, value) ({ \
+ typeof(value) __vec_tmp = (value); \
+ assert(sizeof(__vec_tmp) == \
+ (v)->elem_size); \
+ vec_push_back((v), &__vec_tmp); \
+})
+
+/** @brief Inserts a typed value after checking its size. */
+#define vec_insert_value(v, index, value) ({ \
+ typeof(value) __vec_tmp = (value); \
+ assert(sizeof(__vec_tmp) == \
+ (v)->elem_size); \
+ vec_insert((v), (index), &__vec_tmp); \
+})
+
+/** @brief Reserves a typed slot at the end of the vector. */
+#define vec_emplace_back_as(v, type) \
+ ((type *)vec_emplace_back(v))
+
+/** @brief Reserves a typed slot at the specified index. */
+#define vec_emplace_as(v, type, index) \
+ ((type *)vec_emplace((v), (index)))
+
+
+/** @} */
+
+/** @name Erasure */
+/** @{ */
+
+/** @brief Removes the last element, if one exists. */
+static inline void vec_pop_back(struct vec *v)
+{
+ if (!v || v->size == 0) {
+ return;
+ }
+ v->size--;
+}
+
+/**
+ * @brief Removes the last element and copies it to `out`.
+ * @return `true` on success; `false` when the vector is empty or `out` is null.
+ */
+static inline bool vec_pop_back_copy(struct vec *v,
+ void *out)
+{
+ if (!v || !out || v->size == 0) {
+ return false;
+ }
+ v->size--;
+ const char *last_elem = (const char *)v->data + (v->size * v->elem_size);
+ memcpy(out, last_elem, v->elem_size);
+ return true;
+}
+
+/**
+ * @brief Removes up to `count` elements starting at `index`.
+ */
+static inline void vec_erase_n(struct vec *v,
+ size_t index,
+ size_t count)
+{
+ if (!v || index >= v->size || count == 0) {
+ return;
+ }
+
+ /* Limit the count without allowing index + count to overflow. */
+ if (count > v->size - index) {
+ count = v->size - index;
+ }
+
+ size_t trailing_elems = v->size - (index + count);
+ if (trailing_elems > 0) {
+ char *dest = (char *)v->data + (index * v->elem_size);
+ const char *src = (const char *)v->data + ((index + count) * v->elem_size);
+ /* The source and destination overlap, so use memmove. */
+ memmove(dest, src, trailing_elems * v->elem_size);
+ }
+
+ v->size -= count;
+}
+
+/** @brief Removes the element at `index`, if it exists. */
+static inline void vec_erase(struct vec *v,
+ size_t index)
+{
+ vec_erase_n(v, index, 1);
+}
+
+/**
+ * @brief Removes the half-open range `[first, last)`.
+ * @return A pointer to the element now at `first`, or the end pointer.
+ */
+static inline void *vec_erase_range(struct vec *v,
+ size_t first,
+ size_t last)
+{
+ if (!v || first > last || last > v->size) {
+ return NULL;
+ }
+
+ vec_erase_n(v, first, last - first);
+ if (first == v->size) {
+ if (!v->data) {
+ return NULL;
+ }
+ return (unsigned char *)v->data + v->size * v->elem_size;
+ }
+ return (unsigned char *)v->data + first * v->elem_size;
+}
+
+/** @brief Exchanges the contents of two vectors. */
+static inline void vec_swap(struct vec *a, struct vec *b)
+{
+ struct vec tmp = *a;
+ *a = *b;
+ *b = tmp;
+}
+
+
+/**
+ * @brief Removes an element by replacing it with the last element.
+ *
+ * The order of the remaining elements is not preserved.
+ */
+static inline void vec_swap_erase(struct vec *v,
+ size_t index)
+{
+ if (!v || index >= v->size) {
+ return;
+ }
+
+ size_t last_idx = v->size - 1;
+ /* Move the last element over the erased element when necessary. */
+ if (index < last_idx) {
+ char *dest = (char *)v->data + (index * v->elem_size);
+ const char *src = (const char *)v->data + (last_idx * v->elem_size);
+ memcpy(dest, src, v->elem_size);
+ }
+
+ v->size--;
+}
+
+/** @} */
+
+/** @name Forward iterators */
+/** @{ */
+
+/** @brief Returns a writable iterator to the first element. */
+static inline void *vec_begin(struct vec *v)
+{
+ return v->data;
+}
+
+/** @brief Returns a read-only iterator to the first element. */
+static inline const void *vec_cbegin(const struct vec *v)
+{
+ return v->data;
+}
+
+/** @brief Returns a writable iterator past the last element. */
+static inline void *vec_end(struct vec *v)
+{
+ if (!v->data)
+ return NULL;
+
+ return (unsigned char *)v->data
+ + v->size * v->elem_size;
+}
+
+/** @brief Returns a read-only iterator past the last element. */
+static inline const void *vec_cend(const struct vec *v)
+{
+ if (!v->data)
+ return NULL;
+
+ return (const unsigned char *)v->data
+ + v->size * v->elem_size;
+}
+
+/** @brief Returns the first element as a typed writable iterator. */
+#define vec_begin_as(v, type) \
+ ((type *)vec_begin(v))
+
+/** @brief Returns the end as a typed writable iterator. */
+#define vec_end_as(v, type) \
+ ((type *)vec_end(v))
+
+/** @brief Returns the first element as a typed read-only iterator. */
+#define vec_cbegin_as(v, type) \
+ ((const type *)vec_cbegin(v))
+
+/** @brief Returns the end as a typed read-only iterator. */
+#define vec_cend_as(v, type) \
+ ((const type *)vec_cend(v))
+
+
+/** @} */
+
+/** @name Iterator helpers */
+/** @{ */
+
+/** @brief Advances a pointer iterator by one element. */
+#define vec_iter_next(it) \
+ (++(it))
+
+/** @brief Moves a pointer iterator back by one element. */
+#define vec_iter_prev(it) \
+ (--(it))
+
+/**
+ * @brief Returns the distance between two pointer iterators.
+ *
+ * Equal iterators, including two null pointers, have distance zero.
+ */
+#define vec_iter_distance(first, last) ({ \
+ __auto_type __vec_first = (first); \
+ __auto_type __vec_last = (last); \
+ __vec_first == __vec_last \
+ ? 0 \
+ : __vec_last - __vec_first; \
+})
+
+/**
+ * @brief A reverse iterator over mutable vector storage.
+ */
+struct vec_reverse_iterator {
+ void *data;
+ size_t size;
+ size_t elem_size;
+ size_t offset;
+};
+
+/**
+ * @brief A reverse iterator over read-only vector storage.
+ */
+struct vec_const_reverse_iterator {
+ const void *data;
+ size_t size;
+ size_t elem_size;
+ size_t offset;
+};
+
+/** @brief Returns a reverse iterator to the last element. */
+static inline struct vec_reverse_iterator vec_rbegin(struct vec *v)
+{
+ return (struct vec_reverse_iterator){
+ .data = v->data,
+ .size = v->size,
+ .elem_size = v->elem_size,
+ .offset = 0,
+ };
+}
+
+/** @brief Returns a reverse iterator past the first element. */
+static inline struct vec_reverse_iterator vec_rend(struct vec *v)
+{
+ return (struct vec_reverse_iterator){
+ .data = v->data,
+ .size = v->size,
+ .elem_size = v->elem_size,
+ .offset = v->size,
+ };
+}
+
+/** @brief Returns a read-only reverse iterator to the last element. */
+static inline struct vec_const_reverse_iterator
+vec_crbegin(const struct vec *v)
+{
+ return (struct vec_const_reverse_iterator){
+ .data = v->data,
+ .size = v->size,
+ .elem_size = v->elem_size,
+ .offset = 0,
+ };
+}
+
+/** @brief Returns a read-only reverse iterator past the first element. */
+static inline struct vec_const_reverse_iterator
+vec_crend(const struct vec *v)
+{
+ return (struct vec_const_reverse_iterator){
+ .data = v->data,
+ .size = v->size,
+ .elem_size = v->elem_size,
+ .offset = v->size,
+ };
+}
+
+/** @brief Dereferences a mutable reverse iterator. */
+static inline void *vec_reverse_deref(struct vec_reverse_iterator it)
+{
+ return (unsigned char *)it.data
+ + (it.size - it.offset - 1) * it.elem_size;
+}
+
+/** @brief Dereferences a read-only reverse iterator. */
+static inline const void *
+vec_reverse_deref_const(struct vec_const_reverse_iterator it)
+{
+ return (const unsigned char *)it.data
+ + (it.size - it.offset - 1) * it.elem_size;
+}
+
+/** @brief Advances a mutable reverse iterator. */
+static inline void vec_reverse_next(struct vec_reverse_iterator *it)
+{
+ ++it->offset;
+}
+
+/** @brief Advances a read-only reverse iterator. */
+static inline void
+vec_reverse_next_const(struct vec_const_reverse_iterator *it)
+{
+ ++it->offset;
+}
+
+/** @brief Moves a mutable reverse iterator backwards. */
+static inline void vec_reverse_prev(struct vec_reverse_iterator *it)
+{
+ --it->offset;
+}
+
+/** @brief Moves a read-only reverse iterator backwards. */
+static inline void
+vec_reverse_prev_const(struct vec_const_reverse_iterator *it)
+{
+ --it->offset;
+}
+
+/** @brief Compares two mutable reverse iterators. */
+static inline bool vec_reverse_equal(struct vec_reverse_iterator lhs,
+ struct vec_reverse_iterator rhs)
+{
+ return lhs.data == rhs.data && lhs.offset == rhs.offset;
+}
+
+/** @brief Compares two read-only reverse iterators. */
+static inline bool
+vec_reverse_equal_const(struct vec_const_reverse_iterator lhs,
+ struct vec_const_reverse_iterator rhs)
+{
+ return lhs.data == rhs.data && lhs.offset == rhs.offset;
+}
+
+/** @brief Returns the distance between mutable reverse iterators. */
+static inline ptrdiff_t
+vec_reverse_distance(struct vec_reverse_iterator first,
+ struct vec_reverse_iterator last)
+{
+ return (ptrdiff_t)last.offset - (ptrdiff_t)first.offset;
+}
+
+/** @brief Returns the distance between read-only reverse iterators. */
+static inline ptrdiff_t
+vec_reverse_distance_const(struct vec_const_reverse_iterator first,
+ struct vec_const_reverse_iterator last)
+{
+ return (ptrdiff_t)last.offset - (ptrdiff_t)first.offset;
+}
+
+
+/** @} */
+
+/** @name Traversal */
+/** @{ */
+
+/**
+ * @brief Iterates over mutable vector elements.
+ *
+ * Example:
+ * @code
+ * int *it;
+ * vec_for_each(it, &v, int)
+ * printf("%d\\n", *it);
+ * @endcode
+ */
+
+#define vec_for_each(pos, v, type) \
+ for ((pos) = vec_begin_as((v), type); \
+ (pos) != vec_end_as((v), type); \
+ ++(pos))
+
+/** @brief Iterates over read-only vector elements. */
+#define vec_for_each_const(pos, v, type) \
+ for ((pos) = vec_cbegin_as((v), type); \
+ (pos) != vec_cend_as((v), type); \
+ ++(pos))
+
+/**
+ * @brief Iterates over vector indexes in ascending order.
+ */
+
+#define vec_for_each_index(i, v) \
+ for (size_t i = 0; i < (v)->size; ++i)
+
+/** @brief Iterates over vector indexes in descending order. */
+#define vec_for_each_index_reverse(i, v) \
+ for (size_t i = (v)->size; i-- > 0; )
+
+/** @} */
+
+#endif /* VEC_H */
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