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libc: Implement an actual quicksort for qsort...

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This commit is contained in:
K. Lange 2021-08-28 19:50:54 +09:00
parent a7db67dbb1
commit 7975697786
1 changed files with 40 additions and 12 deletions
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52
libc/stdlib/qsort.c
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@ -1,3 +1,4 @@
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
@ -7,19 +8,46 @@
extern char * _argv_0;
extern int __libc_debug;
void qsort(void * base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)) {
if (!nmemb) return;
if (!size) return;
for (size_t i = 0; i < nmemb-1; ++i) {
for (size_t j = 0; j < nmemb-1; ++j) {
void * left = (char *)base + size * j;
void * right = (char *)base + size * (j + 1);
if (compar(left,right) > 0) {
char tmp[size];
memcpy(tmp, right, size);
memcpy(right, left, size);
memcpy(left, tmp, size);
struct SortableArray {
void * data;
size_t size;
int (*func)(const void *, const void *);
};
static ssize_t partition(struct SortableArray * array, ssize_t lo, ssize_t hi) {
char pivot[array->size];
memcpy(pivot, (char *)array->data + array->size * hi, array->size);
ssize_t i = lo - 1;
for (ssize_t j = lo; j <= hi; ++j) {
uint8_t * obj_j = (uint8_t *)array->data + array->size * j;
if (array->func(obj_j, pivot) <= 0) {
i++;
if (j != i) {
uint8_t * obj_i = (uint8_t *)array->data + array->size * i;
for (size_t x = 0; x < array->size; ++x) {
obj_j[x] ^= obj_i[x];
obj_i[x] ^= obj_j[x];
obj_j[x] ^= obj_i[x];
}
}
}
}
return i;
}
static void quicksort(struct SortableArray * array, ssize_t lo, ssize_t hi) {
if (lo >= 0 && hi >= 0) {
if (lo < hi) {
ssize_t pivot = partition(array, lo, hi);
quicksort(array, lo, pivot - 1);
quicksort(array, pivot + 1, hi);
}
}
}
void qsort(void * base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)) {
if (nmemb < 2) return;
if (!size) return;
struct SortableArray array = {base,size,compar};
quicksort(&array, 0, nmemb - 1);
}