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//===-- Implementation of qsort -------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "src/stdlib/qsort.h"
#include "src/__support/common.h"
#include <stdint.h>
namespace __llvm_libc {
namespace internal {
// A simple quicksort implementation using the Hoare partition scheme.
class Array {
typedef int (*comparator)(const void *, const void *);
uint8_t *array;
size_t array_size;
size_t elem_size;
comparator compare;
public:
Array(uint8_t *a, size_t s, size_t e, comparator c)
: array(a), array_size(s), elem_size(e), compare(c) {}
uint8_t *get(size_t i) const { return array + i * elem_size; }
void swap(size_t i, size_t j) const {
uint8_t *elem_i = get(i);
uint8_t *elem_j = get(j);
for (size_t b = 0; b < elem_size; ++b) {
uint8_t temp = elem_i[b];
elem_i[b] = elem_j[b];
elem_j[b] = temp;
}
}
int elem_compare(size_t i, const uint8_t *other) const {
// An element must compare equal to itself so we don't need to consult the
// user provided comparator.
if (get(i) == other)
return 0;
return compare(get(i), other);
}
size_t size() const { return array_size; }
// Make an Array starting at index |i| and size |s|.
Array make_array(size_t i, size_t s) const {
return Array(get(i), s, elem_size, compare);
}
};
static size_t partition(const Array &array) {
const size_t array_size = array.size();
size_t pivot_index = array_size / 2;
uint8_t *pivot = array.get(pivot_index);
size_t i = 0;
size_t j = array_size - 1;
while (true) {
int compare_i, compare_j;
while ((compare_i = array.elem_compare(i, pivot)) < 0)
++i;
while ((compare_j = array.elem_compare(j, pivot)) > 0)
--j;
// At some point i will crossover j so we will definitely break out of
// this while loop.
if (i >= j)
return j + 1;
array.swap(i, j);
// The pivot itself might have got swapped so we will update the pivot.
if (i == pivot_index) {
pivot = array.get(j);
pivot_index = j;
} else if (j == pivot_index) {
pivot = array.get(i);
pivot_index = i;
}
if (compare_i == 0 && compare_j == 0) {
// If we do not move the pointers, we will end up with an
// infinite loop as i and j will be stuck without advancing.
++i;
--j;
}
}
}
static void quicksort(const Array &array) {
const size_t array_size = array.size();
if (array_size <= 1)
return;
size_t split_index = partition(array);
if (array_size <= 2) {
// The partition operation sorts the two element array.
return;
}
quicksort(array.make_array(0, split_index));
quicksort(array.make_array(split_index, array.size() - split_index));
}
} // namespace internal
LLVM_LIBC_FUNCTION(void, qsort,
(void *array, size_t array_size, size_t elem_size,
int (*compare)(const void *, const void *))) {
if (array == nullptr || array_size == 0 || elem_size == 0)
return;
internal::quicksort(internal::Array(reinterpret_cast<uint8_t *>(array),
array_size, elem_size, compare));
}
} // namespace __llvm_libc
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