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/*
* Copyright (c) 2012, 2014, 2021 Jonas 'Sortie' Termansen.
* Copyright (c) 2021 Juhani 'nortti' Krekelä.
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
* stdlib/qsort_r.c
* Sort an array. Implemented using heapsort, which is not a stable sort.
*/
#include <stdbool.h>
#include <stdlib.h>
static void memswap(unsigned char* a, unsigned char* b, size_t size)
{
unsigned char tmp;
for ( size_t i = 0; i < size; i++ )
{
tmp = a[i];
a[i] = b[i];
b[i] = tmp;
}
}
static unsigned char* array_index(unsigned char* base,
size_t element_size,
size_t index)
{
return base + element_size * index;
}
void qsort_r(void* base_ptr,
size_t num_elements,
size_t element_size,
int (*compare)(const void*, const void*, void*),
void* arg)
{
unsigned char* base = base_ptr;
if ( !element_size || num_elements < 2 )
return;
// Incrementally left-to-right transform the array into a max-heap, where
// each element has up to two children that aren't bigger than the element.
for ( size_t i = 0; i < num_elements; i++ )
{
// Grow the heap by inserting another element into it (implicit, done by
// moving the boundary between the heap and the yet-to-be-processed
// array elements) and swapping it up the parent chain as long as it's
// bigger than its parent.
size_t element = i;
while ( element > 0 )
{
unsigned char* ptr = array_index(base, element_size, element);
size_t parent = (element - 1) / 2;
unsigned char* parent_ptr = array_index(base, element_size, parent);
if ( compare(parent_ptr, ptr, arg) < 0 )
{
memswap(parent_ptr, ptr, element_size);
element = parent;
}
else
break;
}
}
// The array is split into two sections, first the max-heap and then the
// part of the array that has been sorted.
// Sorting progresses right-to-left, taking the biggest value of the heap
// (at its root), swapping it with the last element of the heap, and
// adjusting the boundary between the two sections such that the old biggest
// value is now part of the sorted section.
// After this, the max-heap property is restored by swapping the old last
// element down as long as it's smaller than one of its children.
for ( size_t size = num_elements; --size; )
{
memswap(array_index(base, element_size, size), base, element_size);
size_t first_without_left = size / 2;
size_t first_without_right = (size - 1) / 2;
size_t element = 0;
while ( element < size )
{
unsigned char* ptr = array_index(base, element_size, element);
size_t left = 2 * element + 1;
unsigned char* left_ptr = NULL;
bool left_bigger = false;
if ( element < first_without_left )
{
left_ptr = array_index(base, element_size, left);
left_bigger = compare(ptr, left_ptr, arg) < 0;
}
size_t right = 2 * element + 2;
unsigned char* right_ptr = NULL;
bool right_bigger = false;
if ( element < first_without_right )
{
right_ptr = array_index(base, element_size, right);
right_bigger = compare(ptr, right_ptr, arg) < 0;
}
if ( left_bigger && right_bigger )
{
// If both the left and right child are bigger than the element,
// then swap the element with whichever of the left and right
// child is bigger.
if ( compare(left_ptr, right_ptr, arg) < 0 )
{
memswap(ptr, right_ptr, element_size);
element = right;
}
else
{
memswap(ptr, left_ptr, element_size);
element = left;
}
}
else if ( left_bigger )
{
memswap(ptr, left_ptr, element_size);
element = left;
}
else if ( right_bigger )
{
memswap(ptr, right_ptr, element_size);
element = right;
}
else
break;
}
}
}
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