/** Macro for a generic minimal dynamic array: `MIN_ARRAY(name, type)`, where
 `name` is an identifier prefix that satisfies `C` naming conventions when
 mangled and `type` is defined tag-type associated therewith. When expanding
 the array, resizing may be necessary and incurs amortised cost; any pointers
 to this memory may become stale.
 @param[MIN_ARRAY_CAPACITY] Must be greater than 1; defaults to 3. */

#include <stdlib.h> /* size_t realloc free */
#include <errno.h>  /* errno */
#include <assert.h> /* assert */

#define MIN_ARRAY_IDLE { 0, 0, 0 }
#ifndef MIN_ARRAY_CAPACITY
#define MIN_ARRAY_CAPACITY 3 /* > 1 */
#endif
#define MIN_ARRAY(name, type) \
struct name##_array { type *data; size_t size, capacity; }; \
/** Initialises `a` to idle. */ \
static void name##_array(struct name##_array *const a) \
	{ assert(a); a->data = 0; a->capacity = a->size = 0; } \
/** Destroys `a` and returns it to idle. */ \
static void name##_array_(struct name##_array *const a) \
	{ assert(a); free(a->data); name##_array(a); } \
/** Ensures `min_capacity` of `a`. @return Success; otherwise, `errno` will be
 set. @throws[ERANGE] Tried allocating more then can fit in an object or
 doesn't follow POSIX. @throws[realloc] */ \
static int name##_array_reserve(struct name##_array *const a, \
	const size_t min) { \
	size_t c0; \
	type *data; \
	const size_t max_size = (size_t)-1 / sizeof *a->data; \
	assert(a); \
	if(a->data) { \
		assert(a->size <= a->capacity); \
		if(min <= a->capacity) return 1; \
		c0 = a->capacity < MIN_ARRAY_CAPACITY \
			? MIN_ARRAY_CAPACITY : a->capacity; \
	} else { /* Idle. */ \
		assert(!a->size && !a->capacity); \
		if(!min) return 1; \
		c0 = MIN_ARRAY_CAPACITY; \
	} \
	if(min > max_size) return errno = ERANGE, 0; \
	/* `c_n = a1.625^n`, approximation golden ratio `\phi ~ 1.618`. */ \
	while(c0 < min) { \
		size_t c1 = c0 + (c0 >> 1) + (c0 >> 3); \
		if(c0 > c1) { c0 = max_size; break; } \
		c0 = c1; \
	} \
	if(!(data = realloc(a->data, sizeof *a->data * c0))) \
		{ if(!errno) errno = ERANGE; return 0; } \
	a->data = data, a->capacity = c0; \
	return 1; \
} \
/** Increases the capacity of `a` to at least `n` elements beyond the size.
 @return The start of the buffered space at the back of the array. If `a` is
 idle and `buffer` is zero, a null pointer is returned, otherwise null
 indicates an error. @throws[realloc, ERANGE] */ \
static type *name##_array_buffer(struct name##_array *const a, \
	const size_t n) { \
	assert(a); \
	if(a->size > (size_t)-1 - n) { errno = ERANGE; return 0; } /* Unlikely. */ \
	return name##_array_reserve(a, a->size + n) && a->data \
		? a->data + a->size : 0; \
} \
/** Adds `n` elements to the back of `a`. @return A pointer to the elements. If
 `a` is idle and `n` is zero, a null pointer will be returned, otherwise null
 indicates an error. @throws[realloc, ERANGE] */ \
static type *name##_array_append(struct name##_array *const a, \
	const size_t n) { \
	type *buffer; \
	if(!(buffer = name##_array_buffer(a, n))) return 0; \
	assert(n <= a->capacity && a->size <= a->capacity - n); \
	return a->size += n, buffer; \
} \
/** @return Adds (push back) one new element of `a`.
 @throws[realloc, ERANGE] */ \
static type *name##_array_new(struct name##_array *const a) \
	{ return name##_array_append(a, 1); } \
/* It's perfectly valid that these functions are not used. */ \
static void name##_unused_coda(void); static void name##_unused(void) { \
	name##_array(0); name##_array_new(0); name##_unused_coda(); } \
static void name##_unused_coda(void) { name##_unused(); }