1 files changed, 119 insertions, 0 deletions
diff --git a/unpack/optimize_unpack_order.c b/unpack/optimize_unpack_order.c
new file mode 100644
index 0000000..a76dd51
--- /dev/null
+++ b/unpack/optimize_unpack_order.c
@@ -0,0 +1,119 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * optimize_unpack_order.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "config.h"
+#include "rdsquashfs.h"
+
+static bool has_fragment(const fstree_t *fs, const file_info_t *file)
+{
+	if (file->size % fs->block_size == 0)
+		return false;
+
+	return file->fragment_offset < fs->block_size &&
+		(file->fragment != 0xFFFFFFFF);
+}
+
+static int compare_files(const fstree_t *fs, const file_info_t *lhs,
+			 const file_info_t *rhs)
+{
+	/* NOOP < everything else */
+	if (lhs->input_file == NULL)
+		return rhs->input_file == NULL ? 0 : -1;
+
+	if (rhs->input_file == NULL)
+		return 1;
+
+	/* Files with fragments come first, ordered by ID.
+	   In case of tie, files without data blocks come first,
+	   and the others are ordered by start block. */
+	if (has_fragment(fs, lhs)) {
+		if (!(has_fragment(fs, rhs)))
+			return -1;
+
+		if (lhs->fragment < rhs->fragment)
+			return -1;
+		if (lhs->fragment > rhs->fragment)
+			return 1;
+
+		if (lhs->size < fs->block_size)
+			return (rhs->size < fs->block_size) ? 0 : -1;
+		if (rhs->size < fs->block_size)
+			return 1;
+		goto order_by_start;
+	}
+
+	if (has_fragment(fs, rhs))
+		return 1;
+
+	/* order the rest by start block */
+order_by_start:
+	return lhs->startblock < rhs->startblock ? -1 :
+		lhs->startblock > rhs->startblock ? 1 : 0;
+}
+
+/* TODO: unify ad-hoc merge sort with the one in fstree_sort */
+static file_info_t *merge(const fstree_t *fs, file_info_t *lhs,
+			  file_info_t *rhs)
+{
+	file_info_t *it;
+	file_info_t *head = NULL;
+	file_info_t **next_ptr = &head;
+
+	while (lhs != NULL && rhs != NULL) {
+		if (compare_files(fs, lhs, rhs) <= 0) {
+			it = lhs;
+			lhs = lhs->next;
+		} else {
+			it = rhs;
+			rhs = rhs->next;
+		}
+
+		*next_ptr = it;
+		next_ptr = &it->next;
+	}
+
+	it = (lhs != NULL ? lhs : rhs);
+	*next_ptr = it;
+	return head;
+}
+
+static file_info_t *list_sort(const fstree_t *fs, file_info_t *head)
+{
+	file_info_t *it, *half, *prev;
+
+	it = half = prev = head;
+	while (it != NULL) {
+		prev = half;
+		half = half->next;
+		it = it->next;
+		if (it != NULL) {
+			it = it->next;
+		}
+	}
+
+	// half refers to the (count/2)'th element ROUNDED UP.
+	// It will be null therefore only in the empty and the
+	// single element list
+	if (half == NULL) {
+		return head;
+	}
+
+	prev->next = NULL;
+
+	return merge(fs, list_sort(fs, head), list_sort(fs, half));
+}
+
+file_info_t *optimize_unpack_order(fstree_t *fs)
+{
+	file_info_t *file_list;
+
+	file_list = list_sort(fs, fs->files);
+	while (file_list != NULL && file_list->input_file == NULL)
+		file_list = file_list->next;
+
+	fs->files = NULL;
+	return file_list;
+}