C语言qsort()函数的实现

#include <stdio.h>
void qsort(void * base, int num, int width, int (*comp)(const void *, const void *));
void sort(char * lo, char * hi, int (*comp)(const void *, const void *), int width);
char * partition(char * lo, char * hi, int (*comp)(const void *, const void *), int width);
void swap(char * a, char * b, int width);
int mycomp(const void * p1, const void * p2);

int main(void) {
	int i;
    int a[10] = {5, 3, 2, 9, 12, 6, 7, 10, 11, 1};
	qsort(a, 10, 4, mycomp);
	for (i = 0; i < 10; i++)
		printf("%d ", a[i]);
	printf("\n");

	return 0;
}

int mycomp(const void * p1, const void * p2) {
	const int * a1 = (const int *) p1;
	const int * a2 = (const int *) p2;
	if (*a1 < *a2)
		return -1;
	else if (*a1 == *a2)
		return 0;
	else
		return 1;
}

void qsort(void * base, int num, int width, int (*comp)(const void *, const void *)) {
    char * lo = (char *) base;
    char * hi = (char *) base;
    hi += (num - 1) * width;
    sort(lo, hi, comp, width);
}

void sort(char * lo, char * hi, int (*comp)(const void *, const void *), int width) {
    char * p;
    if (lo >= hi)    return;

    p = partition(lo, hi, comp, width);
    sort(lo, p - width, comp, width);
    sort(p + width, hi, comp, width);
}

char * partition(char * lo, char * hi, int (*comp)(const void *, const void *), int width) {
    char * i = lo;
	char * j = hi;

    while (i <= j) {
        do {
            i += width;
            if (i == hi)   break;
        } while ((*comp)(i, lo) < 0);

        while (1) {
			if ((*comp)(j, lo) <= 0)
				break;
			j -= width;
		}

        if (i <= j)
            swap(i, j, width);
    }
    swap(j, lo, width);
    return j;
}

//swap one byte at a time
void swap(char * a, char * b, int width) {
    char tmp;
    while (width--) {
        tmp = *a;
        *a++ = *b;
        *b++ = tmp;
    }
}