Function update_pre_post_images

apply.c:2433–2494

* Update the preimage, and the common lines in postimage, * from buffer buf of length len. */

 * from buffer buf of length len.
 */
static void update_pre_post_images(struct image *preimage,
				   struct image *postimage,
				   char *buf, size_t len)
{
	struct image fixed_preimage = IMAGE_INIT;
	size_t insert_pos = 0;
	int i, ctx, reduced;
	const char *fixed;

	/*
	 * Update the preimage with whitespace fixes.  Note that we
	 * are not losing preimage->buf -- apply_one_fragment() will
	 * free "oldlines".
	 */
	image_prepare(&fixed_preimage, buf, len, 1);
	for (i = 0; i < fixed_preimage.line_nr; i++)
		fixed_preimage.line[i].flag = preimage->line[i].flag;
	image_clear(preimage);
	*preimage = fixed_preimage;
	fixed = preimage->buf.buf;

	/*
	 * Adjust the common context lines in postimage.
	 */
	for (i = reduced = ctx = 0; i < postimage->line_nr; i++) {
		size_t l_len = postimage->line[i].len;

		if (!(postimage->line[i].flag & LINE_COMMON)) {
			/* an added line -- no counterparts in preimage */
			insert_pos += l_len;
			continue;
		}

		/* and find the corresponding one in the fixed preimage */
		while (ctx < preimage->line_nr &&
		       !(preimage->line[ctx].flag & LINE_COMMON)) {
			fixed += preimage->line[ctx].len;
			ctx++;
		}

		/*
		 * preimage is expected to run out, if the caller
		 * fixed addition of trailing blank lines.
		 */
		if (preimage->line_nr <= ctx) {
			reduced++;
			continue;
		}

		/* and copy it in, while fixing the line length */
		l_len = preimage->line[ctx].len;
		strbuf_splice(&postimage->buf, insert_pos, postimage->line[i].len,
			      fixed, l_len);
		insert_pos += l_len;
		fixed += l_len;
		postimage->line[i].len = l_len;
		ctx++;
	}