qsort.c

Go to the documentation of this file.

/* Copyright (C) 2011 by Valentin Ochs
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

/* Minor changes by Rich Felker for integration in musl, 2011-04-27. */

typedef unsigned int size_t;

#include "atomic.h"
#define ntz(x) a_ctz_l((x))

typedef int (*cmpfun)(const void *, const void *);

static inline int pntz(size_t p[2]) {
        int r = ntz(p[0] - 1);
        if(r != 0 || (r = 8*sizeof(size_t) + ntz(p[1])) != 8*sizeof(size_t)) {
                return r;
        }
        return 0;
}

static void cycle(size_t width, unsigned char* ar[], int n)
{
        unsigned char tmp[256];
        size_t l;
        int i;

        if(n < 2) {
                return;
        }

        ar[n] = tmp;
        while(width) {
                l = sizeof(tmp) < width ? sizeof(tmp) : width;
                memcpy(ar[n], ar[0], l);
                for(i = 0; i < n; i++) {
                        memcpy(ar[i], ar[i + 1], l);
                        ar[i] += l;
                }
                width -= l;
        }
}

/* shl() and shr() need n > 0 */
static inline void shl(size_t p[2], int n)
{
        if(n >= 8 * sizeof(size_t)) {
                n -= 8 * sizeof(size_t);
                p[1] = p[0];
                p[0] = 0;
        }
        p[1] <<= n;
        p[1] |= p[0] >> (sizeof(size_t) * 8 - n);
        p[0] <<= n;
}

static inline void shr(size_t p[2], int n)
{
        if(n >= 8 * sizeof(size_t)) {
                n -= 8 * sizeof(size_t);
                p[0] = p[1];
                p[1] = 0;
        }
        p[0] >>= n;
        p[0] |= p[1] << (sizeof(size_t) * 8 - n);
        p[1] >>= n;
}

static void sift(unsigned char *head, size_t width, int (*cmp)(const void *, const void *), int pshift, size_t lp[])
{
        unsigned char *rt, *lf;
        unsigned char *ar[14 * sizeof(size_t) + 1];
        int i = 1;

        ar[0] = head;
        while(pshift > 1) {
                rt = head - width;
                lf = head - width - lp[pshift - 2];

                if((*cmp)(ar[0], lf) >= 0 && (*cmp)(ar[0], rt) >= 0) {
                        break;
                }
                if((*cmp)(lf, rt) >= 0) {
                        ar[i++] = lf;
                        head = lf;
                        pshift -= 1;
                } else {
                        ar[i++] = rt;
                        head = rt;
                        pshift -= 2;
                }
        }
        cycle(width, ar, i);
}

static void trinkle(unsigned char *head, size_t width, int (*cmp)(const void *, const void *), size_t pp[2], int pshift, int trusty, size_t lp[])
{
        unsigned char *stepson,
                      *rt, *lf;
        size_t p[2];
        unsigned char *ar[14 * sizeof(size_t) + 1];
        int i = 1;
        int trail;

        p[0] = pp[0];
        p[1] = pp[1];

        ar[0] = head;
        while(p[0] != 1 || p[1] != 0) {
                stepson = head - lp[pshift];
                if((*cmp)(stepson, ar[0]) <= 0) {
                        break;
                }
                if(!trusty && pshift > 1) {
                        rt = head - width;
                        lf = head - width - lp[pshift - 2];
                        if((*cmp)(rt, stepson) >= 0 || (*cmp)(lf, stepson) >= 0) {
                                break;
                        }
                }

                ar[i++] = stepson;
                head = stepson;
                trail = pntz(p);
                shr(p, trail);
                pshift += trail;
                trusty = 0;
        }
        if(!trusty) {
                cycle(width, ar, i);
                sift(head, width, cmp, pshift, lp);
        }
}

void qsort(void *base, size_t nel, size_t width, int (*cmp)(const void *, const void *))
{
        size_t lp[12*sizeof(size_t)];
        size_t i, size = width * nel;
        unsigned char *head, *high;
        size_t p[2] = {1, 0};
        int pshift = 1;
        int trail;

        if (!size) return;

        head = base;
        high = head + size - width;

        /* Precompute Leonardo numbers, scaled by element width */
        for(lp[0]=lp[1]=width, i=2; (lp[i]=lp[i-2]+lp[i-1]+width) < size; i++);

        while(head < high) {
                if((p[0] & 3) == 3) {
                        sift(head, width, cmp, pshift, lp);
                        shr(p, 2);
                        pshift += 2;
                } else {
                        if(lp[pshift - 1] >= high - head) {
                                trinkle(head, width, cmp, p, pshift, 0, lp);
                        } else {
                                sift(head, width, cmp, pshift, lp);
                        }
                        
                        if(pshift == 1) {
                                shl(p, 1);
                                pshift = 0;
                        } else {
                                shl(p, pshift - 1);
                                pshift = 1;
                        }
                }
                
                p[0] |= 1;
                head += width;
        }

        trinkle(head, width, cmp, p, pshift, 0, lp);

        while(pshift != 1 || p[0] != 1 || p[1] != 0) {
                if(pshift <= 1) {
                        trail = pntz(p);
                        shr(p, trail);
                        pshift += trail;
                } else {
                        shl(p, 2);
                        pshift -= 2;
                        p[0] ^= 7;
                        shr(p, 1);
                        trinkle(head - lp[pshift] - width, width, cmp, p, pshift + 1, 1, lp);
                        shl(p, 1);
                        p[0] |= 1;
                        trinkle(head - width, width, cmp, p, pshift, 1, lp);
                }
                head -= width;
        }
}