File: rg_ssort.c

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/*
**  ssort()  --  Fast, small, qsort()-compatible Shell sort
**
**  by Ray Gardner,  public domain   5/90
*/

#include <stddef.h>

void ssort (void  *base,
            size_t nel,
            size_t width,
            int (*comp)(const void *, const void *))
{
      size_t wnel, gap, wgap, i, j, k;
      char *a, *b, tmp;

      wnel = width * nel;
      for (gap = 0; ++gap < nel;)
            gap *= 3;
      while ( gap /= 3 )
      {
            wgap = width * gap;
            for (i = wgap; i < wnel; i += width)
            {
                  for (j = i - wgap; ;j -= wgap)
                  {
                        a = j + (char *)base;
                        b = a + wgap;
                        if ( (*comp)(a, b) <= 0 )
                              break;
                        k = width;
                        do
                        {
                              tmp = *a;
                              *a++ = *b;
                              *b++ = tmp;
                        } while ( --k );
                        if (j < wgap)
                              break;
                  }
            }
      }
}