icase - flag, if set to 1 the match is case insensitive
*/
int reg_replace(char** buf_p, int* buf_len_p, char *pattern,
                char *replace, char *string, int icase)
{
  my_regex_t r;
  my_regmatch_t *subs;
  char *replace_end;
  char *buf= *buf_p;
  int len;
  int buf_len, need_buf_len;
  int cflags= MY_REG_EXTENDED;
  int err_code;
  char *res_p,*str_p,*str_end;

  buf_len= *buf_len_p;
  len= strlen(string);
  str_end= string + len;

  /* start with a buffer of a reasonable size that hopefully will not
     need to be reallocated
  */
  need_buf_len= len * 2 + 1;
  res_p= buf;

  SECURE_REG_BUF

  if (icase)
    cflags|= MY_REG_ICASE;

  if ((err_code= my_regcomp(&r,pattern,cflags,&my_charset_latin1)))
  {
    check_regerr(&r,err_code);
    return 1;
  }

  subs= (my_regmatch_t*)my_malloc(PSI_NOT_INSTRUMENTED,
                                  sizeof(my_regmatch_t) * (r.re_nsub+1),
                                  MYF(MY_WME+MY_FAE));

  *res_p= 0;
  str_p= string;
  replace_end= replace + strlen(replace);

  /* for each pattern match instance perform a replacement */
  while (!err_code)
  {
    /* find the match */
    err_code= my_regexec(&r,str_p, r.re_nsub+1, subs,
                         (str_p == string) ? MY_REG_NOTBOL : 0);

    /* if regular expression error (eg. bad syntax, or out of memory) */
    if (err_code && err_code != MY_REG_NOMATCH)
    {
      check_regerr(&r,err_code);
      my_regfree(&r);
      return 1;
    }

    /* if match found */
    if (!err_code)
    {
      char* expr_p= replace;
      int c;

      /*
        we need at least what we have so far in the buffer + the part
        before this match
      */
      need_buf_len= (res_p - buf) + (int) subs[0].rm_so;

      /* on this pass, calculate the memory for the result buffer */
      while (expr_p < replace_end)
      {
        int back_ref_num= -1;
        c= *expr_p;

        if (c == '\\' && expr_p + 1 < replace_end)
        {
          back_ref_num= (int) (expr_p[1] - '0');
        }

        /* found a valid back_ref (eg. \1)*/
        if (back_ref_num >= 0 && back_ref_num <= (int)r.re_nsub)
        {
          my_regoff_t start_off, end_off;
          if ((start_off=subs[back_ref_num].rm_so) > -1 &&
              (end_off=subs[back_ref_num].rm_eo) > -1)
          {
            need_buf_len += (int) (end_off - start_off);
          }
          expr_p += 2;
        }
        else
        {
          expr_p++;
          need_buf_len++;
        }
      }
      need_buf_len++;
      /*
        now that we know the size of the buffer,
        make sure it is big enough
      */
      SECURE_REG_BUF

        /* copy the pre-match part */
        if (subs[0].rm_so)
        {
          memcpy(res_p, str_p, (size_t) subs[0].rm_so);
          res_p+= subs[0].rm_so;
        }

      expr_p= replace;

      /* copy the match and expand back_refs */
      while (expr_p < replace_end)
      {
        int back_ref_num= -1;
        c= *expr_p;

        if (c == '\\' && expr_p + 1 < replace_end)
        {
          back_ref_num= expr_p[1] - '0';
        }

        if (back_ref_num >= 0 && back_ref_num <= (int)r.re_nsub)
        {
          my_regoff_t start_off, end_off;
          if ((start_off=subs[back_ref_num].rm_so) > -1 &&
              (end_off=subs[back_ref_num].rm_eo) > -1)
          {
            int block_len= (int) (end_off - start_off);
            memcpy(res_p,str_p + start_off, block_len);
            res_p += block_len;
          }
          expr_p += 2;
        }
        else
        {
          *res_p++ = *expr_p++;
        }
      }

      /* handle the post-match part */
      if (subs[0].rm_so == subs[0].rm_eo)
      {
        if (str_p + subs[0].rm_so >= str_end)
          break;
        str_p += subs[0].rm_eo ;
        *res_p++ = *str_p++;
      }
      else
      {
        str_p += subs[0].rm_eo;
      }
    }
    else /* no match this time, just copy the string as is */
    {
      int left_in_str= str_end-str_p;
      need_buf_len= (res_p-buf) + left_in_str;
      SECURE_REG_BUF
        memcpy(res_p,str_p,left_in_str);
      res_p += left_in_str;
      str_p= str_end;
    }
  }
  my_free(subs);
  my_regfree(&r);
  *res_p= 0;
  *buf_p= buf;
  *buf_len_p= buf_len;