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natural-mergesort.c
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natural-mergesort.c
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#include "natural-mergesort.h"
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
//get 2^n
size_t fix_capacity(size_t capacity)
{
size_t ret = 1;
while (ret < capacity) {
ret <<= 1;
}
return ret;
}
size_t max(size_t a, size_t b)
{
return a > b ? a : b;
}
run_length_queue* run_length_queue_alloc(size_t capacity)
{
run_length_queue *queue;
//choose larger capacity
capacity = max(capacity, MINIMUM_RUN_LENGTH_QUEUE_CAPACITY);
capacity = fix_capacity(capacity); //become 2^n
queue = malloc(sizeof(*queue)); //allocate memory for self
if (!queue) { //if failed
return NULL;
}
//allocate memory for queue->stirage (length:capacity type:int)
queue->storage = malloc(sizeof(int) * capacity);
if (!queue->storage) { //failed to malloc queue storage
free(queue);
return NULL;
}
//initialize queue
queue->capacity = capacity;
queue->mask = capacity - 1; //for circular queue
queue->head = 0; //starting point
queue->tail = 0; //end point
queue->size = 0; //total in queue
return queue;
}
void run_length_queue_enqueue(run_length_queue *queue, size_t run_size)
{
queue->storage[queue->tail] = run_size;
queue->tail = (queue->tail + 1) & queue->mask;
queue->size++;
}
void run_length_queue_add_to_last(run_length_queue *queue, size_t run_size)
{
queue->storage[(queue->tail - 1) & queue->mask] += run_size;
}
size_t run_length_queue_dequeue(run_length_queue *queue)
{
size_t run_length = queue->storage[queue->head];
queue->head = (queue->head + 1) & queue->mask;
queue->size--;
return run_length;
}
size_t run_length_queue_size(run_length_queue *queue)
{
return queue->size;
}
void run_length_queue_free(run_length_queue *queue)
{
if (queue && queue->storage) {
free(queue->storage);
}
}
void reverse_run(char *base, size_t num, size_t size, void *swap_buffer)
{
size_t left = 0;
size_t right = num - 1;
while (left < right) {
memcpy(swap_buffer, base + size * left, size);
memcpy(base + size * left, base + size * right, size);
memcpy(base + size * right, swap_buffer, size);
++left;
--right;
}
}
run_length_queue*
build_run_length_queue(void *base,
size_t num,
size_t size,
int (*cmp)(const void*, const void*))
{
run_length_queue *queue;
size_t head;
size_t left;
size_t right;
size_t last;
size_t run_length;
bool previous_was_descending;
void *swap_buffer = malloc(size);
queue = run_length_queue_alloc((num >> 1) + 1); //allocate (num/2+1) size (will resize to 2^n or 256) queue
if (!queue) { //if failed
return NULL;
}
//initialize
left = 0;
right = 1;
last = num - 1;
previous_was_descending = false;
while (left < last) {
head = left;
/* Decide the direction of the next run. */
if (cmp(((char*) base) + size * left++,
((char*) base) + size * right++) <= 0) {
/* The run is ascending. */
while (left < last
&& cmp(((char*) base) + size * left,
((char*) base) + size * right) <= 0) {
++left;
++right;
}
//calculate length
run_length = left - head + 1;
//if previous is descending (acturally it became ascending) , check if this can comibne with it
//data will become desc asc desc asc ... it may be combined only if previous is descending
if (previous_was_descending) {
if (cmp(((char*) base) + (head - 1) * size,
((char*) base) + head * size) <= 0) {
run_length_queue_add_to_last(queue, run_length);
} else {
run_length_queue_enqueue(queue, run_length);
}
} else {
run_length_queue_enqueue(queue, run_length);
}
previous_was_descending = false;
} else {
/* Scan a strictly descending run. */
while (left < last
&& cmp(((char*) base) + size * left,
((char*) base) + size * right) > 0) {
++left;
++right;
}
run_length = left - head + 1;
reverse_run(((char*) base) + head * size,
run_length,
size,
swap_buffer);
if (previous_was_descending) {
if (cmp(((char*) base) + size * (head - 1),
((char*) base) + size * head) <= 0) {
run_length_queue_add_to_last(queue, run_length);
} else {
run_length_queue_enqueue(queue, run_length);
}
} else {
run_length_queue_enqueue(queue, run_length);
}
previous_was_descending = true;
}
++left;
++right;
}
if (left == last) { //tackle last element
if (cmp(((char*) base) + size * (last - 1),
((char*) base) + size * last) <= 0) {
run_length_queue_add_to_last(queue, 1);
} else {
run_length_queue_enqueue(queue, 1);
}
}
free(swap_buffer);
return queue;
}
void merge(void *source,
void *target,
size_t size,
size_t offset,
size_t left_run_length,
size_t right_run_length,
int (*cmp)(const void*, const void*))
{
size_t left = offset;
size_t right = left + left_run_length;
const size_t left_bound = right;
const size_t right_bound = right + right_run_length;
size_t target_index = offset;
while (left < left_bound && right < right_bound) {
if (cmp(((char*) source) + size * right,
((char*) source) + size * left) < 0) {
/* right is smaller */
memcpy(((char*) target) + size * target_index,
((char*) source) + size * right,
size);
++right;
} else {
memcpy(((char*) target) + size * target_index,
((char*) source) + size * left,
size);
++left;
}
++target_index;
}
memcpy(((char*) target) + size * target_index,
((char*) source) + size * left,
(left_bound - left) * size);
memcpy(((char*) target) + size * target_index,
((char*) source) + size * right,
(right_bound - right) * size);
}
size_t get_number_of_leading_zeros(size_t number)
{
size_t mask = 1;
size_t number_of_leading_zeros = 0;
mask <<= (sizeof number) * BITS_PER_BYTE - 1;
while (mask && ((mask & number) == 0)) {
++number_of_leading_zeros;
mask >>= 1;
}
return number_of_leading_zeros;
}
size_t get_number_of_merge_passes(size_t runs)
{
//calculate size-clz
return sizeof(size_t) * BITS_PER_BYTE -
get_number_of_leading_zeros(runs - 1); //runs-1 ex:8runs(0001000)to 1 3 levels
}
/*
base :array pointer
num :data number
size :size of each element
comparator:comparator function
*/
void stable_sort(void *base, size_t num, size_t size, int (*comparator)(const void*, const void*))
{
run_length_queue *queue;
void *buffer;
void *source;
void *target;
void *tmp;
size_t offset;
size_t merge_passes;
size_t runs_remaining;
size_t tail_run_length;
size_t left_run_length;
size_t right_run_length;
//if wrong input
if (!base || !comparator || num < 2 || size == 0) {
return;
}
buffer = malloc(num * size);
// if failed to allocate memory for buffer >>> use qsort
if (!buffer) {
qsort(base, num, size, comparator);
return;
}
//build queue
queue = build_run_length_queue(base, num, size, comparator);
if (!queue) {
/* Cannot allocate the run length queue. Resort to qsort and possibly
fail in the same manner as qsort. */
qsort(base, num, size, comparator);
return;
}
// calcutlate the "level" of merge
merge_passes = get_number_of_merge_passes(run_length_queue_size(queue));
if ((merge_passes & 1) == 1) { //if odd
source = buffer;
target = base;
memcpy(buffer, base, num * size); //copy data to buffer, buffer is source
}// update state -> base -> buffer ->base -> buffer ->base
else { //if even -> don't copy, base is source, final target is base
source = base;
target = buffer;
}// update state -> buffer ->base -> buffer ->base -> buffer ->base
offset = 0; //data offset
runs_remaining = run_length_queue_size(queue); //get queue's size
// runs_remaining:the number of block in queue which is not tackled yet
while (run_length_queue_size(queue) > 1) {
left_run_length = run_length_queue_dequeue(queue); //get left array size
right_run_length = run_length_queue_dequeue(queue); //get right array size
merge(source,
target,
size,
offset,
left_run_length,
right_run_length,
comparator);
run_length_queue_enqueue(queue, left_run_length + right_run_length); //put into queue
runs_remaining -= 2;
offset += left_run_length + right_run_length;
switch (runs_remaining) {
case 1: //if these remains one block which can't make a pair
tail_run_length = run_length_queue_dequeue(queue); //pop
memcpy(((char*) target) + offset * size,
((char*) source) + offset * size,
size * tail_run_length);
run_length_queue_enqueue(queue, tail_run_length); //push
/* FALL THROUGH! */
case 0:
runs_remaining = run_length_queue_size(queue); //reget queue
offset = 0; //initialize to zero
/*change source and target*/
tmp = source;
source = target;
target = tmp;
break;
}
}
//free queue buffer
run_length_queue_free(queue);
free(buffer);
}