lib/qsort.c

   1 /*
   2  * Code adapted from uClibc-0.9.30.3
   3  *
   4  * It is therefore covered by the GNU LESSER GENERAL PUBLIC LICENSE
   5  * Version 2.1, February 1999
   6  *
   7  * Wolfgang Denk <wd@denx.de>
   8  */
   9
  10 /* This code is derived from a public domain shell sort routine by
  11  * Ray Gardner and found in Bob Stout's snippets collection.  The
  12  * original code is included below in an #if 0/#endif block.
  13  *
  14  * I modified it to avoid the possibility of overflow in the wgap
  15  * calculation, as well as to reduce the generated code size with
  16  * bcc and gcc. */
  17
  18 #include <linux/types.h>
  19 #if 0
  20 #include <assert.h>
  21 #else
  22 #define assert(arg)
  23 #endif
  24
  25 void qsort(void  *base,
  26            size_t nel,
  27            size_t width,
  28            int (*comp)(const void *, const void *))
  29 {
  30         size_t wgap, i, j, k;
  31         char tmp;
  32
  33         if ((nel > 1) && (width > 0)) {
  34                 assert(nel <= ((size_t)(-1)) / width); /* check for overflow */
  35                 wgap = 0;
  36                 do {
  37                         wgap = 3 * wgap + 1;
  38                 } while (wgap < (nel-1)/3);
  39                 /* From the above, we know that either wgap == 1 < nel or */
  40                 /* ((wgap-1)/3 < (int) ((nel-1)/3) <= (nel-1)/3 ==> wgap <  nel. */
  41                 wgap *= width;                  /* So this can not overflow if wnel doesn't. */
  42                 nel *= width;                   /* Convert nel to 'wnel' */
  43                 do {
  44                         i = wgap;
  45                         do {
  46                                 j = i;
  47                                 do {
  48                                         register char *a;
  49                                         register char *b;
  50
  51                                         j -= wgap;
  52                                         a = j + ((char *)base);
  53                                         b = a + wgap;
  54                                         if ((*comp)(a, b) <= 0) {
  55                                                 break;
  56                                         }
  57                                         k = width;
  58                                         do {
  59                                                 tmp = *a;
  60                                                 *a++ = *b;
  61                                                 *b++ = tmp;
  62                                         } while (--k);
  63                                 } while (j >= wgap);
  64                                 i += width;
  65                         } while (i < nel);
  66                         wgap = (wgap - width)/3;
  67                 } while (wgap);
  68         }
  69 }