Dear monks,

I try to develop a faster Diff/LCS than Algorithm::Diff::XS or LCS::BV.

My first approach with two strings to C looked promising with rates of 400 KHz for length ~10 (result 7 x 2 array). This is 8 times the speed of A::D::XS. But adding the composition of the resulting alignment as Array of Arrays slowed down the rate to 190 KHz. A more extreme case s1 = a..zA..Y, s2 = b..zA..Z, with only the first and last element different, drops down from 333 KHz to 60 KHz. That's because the result is a 50 x 2 array.

Here is the suspiciously slow part (see also on CPAN module LCS::XS or github.com/wollmers/LCS-XS):

void lcs_LCS(obj, s1, s2)
    SV *obj
    AV * s1
    AV * s2

    PREINIT:
        struct CTX *ctx = (struct CTX *)SvIVX(SvRV(obj));

    PPCODE:
        int d, sn, i;
        struct varray *ses = varray_new(sizeof(struct diff_edit), NULL
+);
  
        IV n;
        IV m;
        n = av_top_index(s1);
        m = av_top_index(s2);

        d = diff(s1, 0, n+1, s2, 0, m+1, &_cmp_idx,  NULL, 0, ses, &sn
+, NULL);

 
  int x,y,j;
  x=y=0;

  XSprePUSH;

  for (i = 0; i < sn; i++) {
      struct diff_edit *e = varray_get(ses, i);
  
      switch (e->op) {
          case DIFF_MATCH:
              //printf("MAT: ");
              //printf("off %d len %d\n", e->off, e->len);
              for (j = 0; j < e->len; j++) {
                //printf("x %d y %d\n", x, y);
                
                AV *arr;
              arr = newAV();
              av_push(arr, newSViv(x));
              av_push(arr, newSViv(y));
              XPUSHs(sv_2mortal(newRV_noinc((SV *)arr)));
                    
                x++;
                y++;
              }
              break;
          case DIFF_DELETE:
              //printf("DEL: ");
              //printf("off %d len %d\n", e->off, e->len);
              for (j = 0; j < e->len; j++) {
                x++;
              }
              break;
          case DIFF_INSERT:
              //printf("INS: ");
              //printf("off %d len %d\n", e->off, e->len);
              for (j = 0; j < e->len; j++) {
                y++;
              }
              break;
      }
  }

                
                
  varray_del(ses);
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