snapraid/tommyds/tommyarray.h

// SPDX-License-Identifier: BSD-2-Clause
// Copyright (C) 2011 Andrea Mazzoleni

/** \file
 * Dynamic array based on segments of exponentially growing size.
 *
 * This array is able to grow dynamically upon request, without any reallocation.
 *
 * The grow operation involves an allocation of a new array segment, without reallocating
 * the already used memory, and thus **not increasing** the heap fragmentation.
 * This also implies that the address of the stored elements never changes.
 *
 * Allocated segments grow in size exponentially.
 */

#ifndef TOMMY_ARRAY_H
#define TOMMY_ARRAY_H

#include "tommytypes.h"

#include <assert.h> /* for assert */

/******************************************************************************/
/* array */

/**
 * Initial and minimal size of the array expressed as a power of 2.
 * The initial size is 2^TOMMY_ARRAY_BIT.
 */
#define TOMMY_ARRAY_BIT 6

/**
 * Array container type.
 * \note Don't use internal fields directly, but access the container only using functions.
 */
typedef struct tommy_array_struct {
	void** bucket[TOMMY_SIZE_BIT]; /**< Dynamic array of buckets. */
	tommy_size_t bucket_max; /**< Number of buckets. */
	tommy_size_t count; /**< Number of initialized elements in the array. */
	tommy_uint_t bucket_bit; /**< Bits used in the bit mask. */
} tommy_array;

/**
 * Initializes the array.
 */
TOMMY_API void tommy_array_init(tommy_array* array);

/**
 * Deinitializes the array.
 */
TOMMY_API void tommy_array_done(tommy_array* array);

/**
 * Allocates space for at least the specified number of elements.
 * The initialized size and existing elements are unchanged.
 * Existing element references remain valid.
 */
TOMMY_API void tommy_array_reserve(tommy_array* array, tommy_size_t size);

/**
 * Grows the size up to the specified value.
 * All the new elements in the array are initialized with the 0 value.
 */
tommy_inline void tommy_array_grow(tommy_array* array, tommy_size_t size)
{
	if (size > array->count) {
		array->count = size;

		if (size > array->bucket_max)
			tommy_array_reserve(array, size);
	}
}

/**
 * Changes the initialized size, preserving the common prefix.
 * New elements are initialized to zero.
 * Reducing the size does not release allocated capacity.
 */
TOMMY_API void tommy_array_resize(tommy_array* array, tommy_size_t size);

/**
 * Removes all elements, preserving the allocated capacity.
 * Call tommy_array_shrink() after clearing to restore the initial capacity.
 * Pointed-to objects are not freed.
 * The array remains initialized and can be reused immediately.
 */
tommy_inline void tommy_array_clear(tommy_array* array)
{
	tommy_array_resize(array, 0);
}

/**
 * Releases unused allocated memory.
 * Preserves the size, values, and addresses of existing elements.
 */
TOMMY_API void tommy_array_shrink(tommy_array* array);

/**
 * Gets a reference to the element at the specified position.
 * You must be sure that space for this position is already
 * allocated by calling tommy_array_grow().
 */
tommy_inline void** tommy_array_ref(tommy_array* array, tommy_size_t pos)
{
	assert(pos < array->count);

	/* get the highest bit set, in case of all 0, return 0 */
	tommy_uint_t bsr = tommy_ilog2(pos | 1);

	return &array->bucket[bsr][pos];
}

/**
 * Sets the element at the specified position.
 * You must be sure that space for this position is already
 * allocated by calling tommy_array_grow().
 */
tommy_inline void tommy_array_set(tommy_array* array, tommy_size_t pos, void* element)
{
	*tommy_array_ref(array, pos) = element;
}

/**
 * Gets the element at the specified position.
 * You must be sure that space for this position is already
 * allocated by calling tommy_array_grow().
 */
tommy_inline void* tommy_array_get(tommy_array* array, tommy_size_t pos)
{
	return *tommy_array_ref(array, pos);
}

/**
 * Gets the last element.
 * The array must not be empty.
 */
tommy_inline void* tommy_array_tail(tommy_array* array)
{
	assert(array->count != 0);
	return tommy_array_get(array, array->count - 1);
}

/**
 * Grows and inserts a new element at the end of the array.
 */
tommy_inline void tommy_array_insert_tail(tommy_array* array, void* element)
{
	tommy_size_t pos = array->count;

	tommy_array_grow(array, pos + 1);

	tommy_array_set(array, pos, element);
}

/**
 * Removes and returns the last element.
 * The array must not be empty.
 * The removed slot is cleared, and allocated capacity is preserved.
 */
tommy_inline void* tommy_array_remove_tail(tommy_array* array)
{
	assert(array->count != 0);

	tommy_size_t pos = array->count - 1;
	void** ptr = tommy_array_ref(array, pos);
	void* element = *ptr;

	/* keep unused slots zero so growing within capacity needs no initialization */
	*ptr = 0;
	array->count = pos;

	return element;
}

/**
 * Checks whether the array is empty.
 */
tommy_inline tommy_bool_t tommy_array_empty(const tommy_array* array)
{
	return array->count == 0;
}

/**
 * Gets the initialized size of the array.
 */
tommy_inline tommy_size_t tommy_array_size(const tommy_array* array)
{
	return array->count;
}

/**
 * Gets the number of elements that fit without further allocation.
 */
tommy_inline tommy_size_t tommy_array_capacity(const tommy_array* array)
{
	return array->bucket_max;
}

/**
 * Exchanges two initialized arrays without copying their elements.
 * Element references remain valid and belong to the other array.
 * Passing the same array twice has no effect.
 */
tommy_inline void tommy_array_swap(tommy_array* first, tommy_array* second)
{
	tommy_array tmp = *first;
	*first = *second;
	*second = tmp;
}

/**
 * Calls the specified function for each element in the array.
 *
 * You cannot add or remove elements, nor change the size of the array,
 * from inside the callback.
 *
 * \param array Array to iterate.
 * \param func Function to call with each element.
 *
 * If the callback frees the objects, the array retains dangling
 * pointers. Call tommy_array_clear() before reusing it, or
 * tommy_array_done() to release its storage.
 */
TOMMY_API void tommy_array_foreach(tommy_array* array, tommy_foreach_func* func);

/**
 * Calls the specified function with an argument for each element in the array.
 *
 * \param array Array to iterate.
 * \param func Function to call with each element.
 * \param arg Argument to pass to the function.
 */
TOMMY_API void tommy_array_foreach_arg(tommy_array* array, tommy_foreach_arg_func* func, void* arg);

/**
 * Gets the size of allocated memory.
 */
TOMMY_API tommy_size_t tommy_array_memory_usage(const tommy_array* array);

#endif