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-rw-r--r--delta.h22
1 files changed, 22 insertions, 0 deletions
diff --git a/delta.h b/delta.h
index bc3a220..31d1820 100644
--- a/delta.h
+++ b/delta.h
@@ -9,4 +9,26 @@ extern void *patch_delta(void *src_buf, unsigned long src_size,
void *delta_buf, unsigned long delta_size,
unsigned long *dst_size);
+/* the smallest possible delta size is 4 bytes */
+#define DELTA_SIZE_MIN 4
+
+/*
+ * This must be called twice on the delta data buffer, first to get the
+ * expected reference buffer size, and again to get the result buffer size.
+ */
+static inline unsigned long get_delta_hdr_size(const unsigned char **datap)
+{
+ const unsigned char *data = *datap;
+ unsigned char cmd = *data++;
+ unsigned long size = cmd & ~0x80;
+ int i = 7;
+ while (cmd & 0x80) {
+ cmd = *data++;
+ size |= (cmd & ~0x80) << i;
+ i += 7;
+ }
+ *datap = data;
+ return size;
+}
+
#endif