scummvm/common/algorithm.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#ifndef COMMON_ALGORITHM_H
#define COMMON_ALGORITHM_H

#include "common/scummsys.h"
#include "common/func.h"
#include "common/util.h"

namespace Common {

/**
 * @defgroup common_alg Algorithms
 * @ingroup common
 *
 * @brief Templates for algorithms used to manipulate data.
 *
 * @{
 */

/**
 * @name Copy templates
 * @{
 */

/**
 * Copy data from the range [first, last) to [dst, dst + (last - first)).
 *
 * The function requires the range [dst, dst + (last - first)) to be valid.
 * It also requires dst not to be in the range [first, last).
 */
template<class In, class Out>
Out copy(In first, In last, Out dst) {
	while (first != last)
		*dst++ = *first++;
	return dst;
}

/**
 * Copy data from the range [first, last) to [dst - (last - first), dst).
 *
 * The function requires the range [dst - (last - first), dst) to be valid.
 * It also requires dst not to be in the range [first, last).
 *
 * Unlike copy, copy_backward copies the data from the end to the beginning.
 */
template<class In, class Out>
Out copy_backward(In first, In last, Out dst) {
	while (first != last)
		*--dst = *--last;
	return dst;
}

/**
 * Copy data from the range [first, last) to [dst, dst + (last - first)).
 *
 * The function requires the range [dst, dst + (last - first)) to be valid.
 * It also requires dst not to be in the range [first, last).
 *
 * Unlike copy or copy_backward, it does not copy all data. It only copies
 * a data element when operator() of the op parameter returns true for the
 * passed data element.
 */
template<class In, class Out, class Op>
Out copy_if(In first, In last, Out dst, Op op) {
	while (first != last) {
		if (op(*first))
			*dst++ = *first;
		++first;
	}
	return dst;
}

/**
 * @}
 */

/**
 * @name Fill templates
 * @{
 */

/**
 * A 'fill' template for signed char arrays.
 *
 * Since C++ does not currently support partial specialized template functions,
 * this solution is implemented.
 * With this template, the usage of memset is assured, which is
 * faster than a simple loop like for the generic 'fill'.
 */
template<class Value>
signed char *fill(signed char *first, signed char *last, Value val) {
	memset(first, (val & 0xFF), last - first);
	return last;
}

/**
 * A 'fill' template for unsigned char arrays.
 *
 * Since C++ does not currently support partial specialized template functions,
 * this solution is implemented.
 * With this template, the usage of memset is assured, which is
 * faster than a simple loop like for the generic 'fill'.
 */
template<class Value>
unsigned char *fill(unsigned char *first, unsigned char *last, Value val) {
	memset(first, (val & 0xFF), last - first);
	return last;
}

/**
 * A 'fill' template for char arrays.
 *
 * Since C++ does not currently support partial specialized template functions,
 * this solution is implemented.
 * With this template, the usage of memset is assured, which is
 * faster than a simple loop like for the generic 'fill'.
 */
template<class Value>
char *fill(char *first, char *last, Value val) {
	memset(first, (val & 0xFF), last - first);
	return last;
}

/**
 * @}
 */

/**
 * @name Range templates
 * @{
 */

/**
 * Set all elements in the range [first, last) to val.
 */
template<class In, class Value>
In fill(In first, In last, const Value &val) {
	while (first != last)
		*first++ = val;
	return first;
}

/**
 * Find the first data value in the range [first, last) matching v.
 * For data comparison, it uses operator == of the data elements.
 */
template<class In, class T>
In find(In first, In last, const T &v) {
	while (first != last) {
		if (*first == v)
			return first;
		++first;
	}
	return last;
}

/**
 * Find the first data value in the range [first, last), for which
 * the specified predicate p returns true.
 */
template<class In, class Pred>
In find_if(In first, In last, Pred p) {
	while (first != last) {
		if (p(*first))
			return first;
		++first;
	}
	return last;
}

/**
 * Apply the function f on all elements from the range [first, last).
 * The processing order is from beginning to end.
 */
template<class In, class Op>
Op for_each(In first, In last, Op f) {
	while (first != last)
		f(*first++);
	return f;
}

/**
 * @}
 */

template<typename T>
unsigned int distance(T *first, T *last) {
	return last - first;
}

template<typename T>
unsigned int distance(T first, T last) {
	unsigned int n = 0;
	while (first != last) {
		++n;
		++first;
	}
	return n;
}

template<typename T>
T *sortChoosePivot(T *first, T *last) {
	return first + distance(first, last) / 2;
}

template<typename T>
T sortChoosePivot(T first, T last) {
	unsigned int n = distance(first, last);
	n /= 2;
	while (n--)
		++first;
	return first;
}

template<typename T, class StrictWeakOrdering>
T sortPartition(T first, T last, T pivot, StrictWeakOrdering &comp) {
	--last;
	if (pivot != last)
		SWAP(*pivot, *last);

	T sorted;
	for (sorted = first; first != last; ++first) {
		if (!comp(*last, *first)) {
			if (first != sorted)
				SWAP(*first, *sorted);
			++sorted;
		}
	}

	if (last != sorted)
		SWAP(*last, *sorted);
	return sorted;
}

/**
 * @name Sorting templates
 * @{
 */

/**
 * Simple sorting function, modeled after std::sort.
 *
 * This function compares data with the given comparator object comp.
 *
 * Like std::sort, this is not guaranteed to be stable.
 *
 * Two quotes from Wikipedia about stability:
 *
 * Stable sorting algorithms maintain the relative order of records with
 * equal keys.
 *
 * Unstable sorting algorithms may change the relative order of records with
 * equal keys, but stable sorting algorithms never do so.
 *
 * For more information, see:
 * http://en.wikipedia.org/wiki/Sorting_algorithm#Stability
 *
 * @note Currently, this implementation is unstable.
 *
 * @param[in] first First element to sort.
 * @param[in] last  Last element to sort.
 * @param[in] comp  Comparator object.
 */

template<typename T, class StrictWeakOrdering>
void sort(T first, T last, StrictWeakOrdering comp) {
	if (first == last)
		return;

	T pivot = sortChoosePivot(first, last);
	pivot = sortPartition(first, last, pivot, comp);
	sort<T, StrictWeakOrdering>(first, pivot, comp);
	sort<T, StrictWeakOrdering>(++pivot, last, comp);
}

/**
 * Simple sorting function, modeled after std::sort.
 *
 * @param[in] first First element to sort.
 * @param[in] last  Last element to sort.
 */
template<typename T>
void sort(T *first, T *last) {
	sort(first, last, Less<T>());
}

/**
 * Simple sorting function, modeled after std::sort.
 *
 * @param[in] first First element to sort.
 * @param[in] last  Last element to sort.
 */

template<class T>
void sort(T first, T last) {
	sort(first, last, Less<typename T::ValueType>());
}

/**
 * @}
 */

// MSVC is complaining about the minus operator being applied to an unsigned type
// We disable this warning for the affected section of code
#if defined(_MSC_VER)
#pragma warning(push)
#pragma warning(disable: 4146)
#endif

/**
 * Euclidean algorithm to compute the greatest common divisor.
 */
template<class T>
T gcd(T a, T b) {
	// Note: We check for <= instead of < to avoid spurious compiler
	// warnings if T is an unsigned type, i.e. warnings like "comparison
	// of unsigned expression < 0 is always false".
	if (a <= 0)
		a = -a;
	if (b <= 0)
		b = -b;

	while (a > 0) {
		T tmp = a;
		a = b % a;
		b = tmp;
	}

	return b;
}

#if defined(_MSC_VER)
#pragma warning(pop)
#endif

/**
 * Get the next highest power of 2.
 */
template<class T>
T nextHigher2(T v) {
	if (v == 0)
		return 1;
	v--;
	v |= v >> 1;
	v |= v >> 2;
	v |= v >> 4;
	v |= v >> 8;
	v |= v >> 16;
	return ++v;
}

/**
 * Replacement algorithm for iterables.
 *
 * Replaces all occurrences of "original" in [begin, end) with occurrences of "replaced".
 *
 * @param[in,out] begin    First element to be examined.
 * @param[in]     end      Last element in the subsection. Not examined.
 * @param[in]     original Elements to be replaced.
 * @param[in]     replaced Element to replace occurrences of @p original.
 *
 * @note Usage examples and unit tests may be found in "test/common/algorithm.h"
 */
template<class It, class Dat>
void replace(It begin, It end, const Dat &original, const Dat &replaced) {
	for (; begin != end; ++begin) {
		if (*begin == original) {
			*begin = replaced;
		}
	}
}

/**
 * Removes all elements that are equal to value from the range [first, last).
 * This function is the equivalent of std::remove.
 * 
 * @param[in] first Iterator to the first position to be examined.
 * @param[in] last  Iterator to the last position.
 * @param[in] val   Value to be removed.
 * @return          An iterator to the new end of the range.
 */
template<class It, class T>
It remove(It first, It last, const T& val) {
	first = find(first, last, val);
	if (first != last) {
		It i = first;
		while (++i != last) {
			if (!(*i == val)) {
				*first = move(*i);
				first++;
			}
		}
	}
	return first;
}

/**
 * Returns an iterator to the first item in the range [first, last) for which comp(item, val)
 * (item < val by default) is false, or last if no such item is found.
 * Items in the range [first, last) need to be partitioned by comp(item, val), that is,
 * all items for which comp(item, val) is true (items that are less than val)
 * come before all items for which the expression is false (items that are bigger than or
 * equal to val). A sorted range conforms to the requirement.
 *
 * This function is the equivalent of std::lower_bound for random access iterators.
 */
template<typename RandomIt, typename V, typename Comp = Less<V> >
RandomIt lowerBound(RandomIt first, RandomIt last, const V &val, Comp comp = {}) {
	while (first < last) {
		const RandomIt mid = first + distance(first, last) / 2;
		if (comp(*mid, val))
			first = mid + 1;
		else
			last = mid;
	}
	return first;
}

/**
 * Returns an iterator to the first item in the range [first, last) for which comp(val, item)
 * (val < item by default) is true, or last if no such item is found.
 * Items in the range [first, last) need to be partitioned by !comp(val, item), that is,
 * all items for which !comp(val, item) is true (items that are less than or equal to val),
 * come before all items for which the expression is false (items that are greater than val).
 * A sorted range conforms to the requirement.
 *
 * This function is the equivalent of std::upper_bound for random access iterators.
 */
template<typename RandomIt, typename V, typename Comp = Less<V> >
RandomIt upperBound(RandomIt first, RandomIt last, const V &val, Comp comp = {}) {
	while (first < last) {
		const RandomIt mid = first + distance(first, last) / 2;
		if (!comp(val, *mid))
			first = mid + 1;
		else
			last = mid;
	}
	return first;
}

/** @} */

} // End of namespace Common

#endif