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sortix--sortix/libc/stdlib/qsort_r.cpp

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/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2012, 2014.
This file is part of the Sortix C Library.
The Sortix C Library is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
The Sortix C Library 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 Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
stdlib/qsort_r.cpp
Sort an array.
*******************************************************************************/
#include <stdlib.h>
#include <string.h>
static void memswap(unsigned char* a, unsigned char* b, size_t size)
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{
unsigned char tmp;
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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;
}
static
size_t partition(unsigned char* base,
size_t element_size,
size_t num_elements,
size_t pivot_index,
int (*compare)(const void*, const void*, void*),
void* arg)
{
if ( pivot_index != num_elements - 1 )
{
unsigned char* pivot = array_index(base, element_size, pivot_index);
unsigned char* other = array_index(base, element_size, num_elements - 1);
memswap(pivot, other, element_size);
pivot_index = num_elements - 1;
}
size_t store_index = 0;
for ( size_t i = 0; i < num_elements - 1; i++ )
{
unsigned char* pivot = array_index(base, element_size, pivot_index);
unsigned char* value = array_index(base, element_size, i);
if ( compare(value, pivot, arg) <= 0 )
{
unsigned char* other = array_index(base, element_size, store_index);
if ( value != other )
memswap(value, other, element_size);
store_index++;
}
}
unsigned char* pivot = array_index(base, element_size, pivot_index);
unsigned char* value = array_index(base, element_size, store_index);
memswap(pivot, value, element_size);
return store_index;
}
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extern "C"
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 = (unsigned char*) base_ptr;
if ( !element_size || num_elements < 2 )
return;
size_t pivot_index = num_elements / 2;
pivot_index = partition(base, element_size, num_elements, pivot_index, compare, arg);
if ( 2 <= pivot_index )
qsort_r(base, pivot_index, element_size, compare, arg);
if ( 2 <= num_elements - (pivot_index + 1) )
qsort_r(array_index(base, element_size, pivot_index + 1),
num_elements - (pivot_index + 1), element_size, compare, arg);
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}