vim-55/src/regexp.c

6806     char_u	*newsub = source;
6812     for (p = newsub; *p; ++p)
6818 		/* length = len(newsub) - 1 + len(prev_sub) + 1 */
6820 		tmpsub = alloc((unsigned)(STRLEN(newsub) + prevlen));
6824 		    len = (int)(p - newsub);	/* not including ~ */
6825 		    mch_memmove(tmpsub, newsub, (size_t)len);
6833 		    if (newsub != source)	/* already allocated newsub */
6834 			vim_free(newsub);
6835 		    newsub = tmpsub;
6836 		    p = newsub + len + prevlen;
6857     if (newsub != source)	/* newsub was allocated, just keep it */
6858 	reg_prev_sub = newsub;
6859     else			/* no ~ found, need to save newsub  */
6860 	reg_prev_sub = vim_strsave(newsub);
6861     return newsub;