[PATCH] Deltification library work by Nicolas Pitre.

[thirdparty/git.git] / patch-delta.c

diff --git a/patch-delta.c b/patch-delta.c
new file mode 100644 (file)
index 0000000..a8d75ee
--- /dev/null
+++ b/patch-delta.c
@@ -0,0 +1,88 @@
+/*
+ * patch-delta.c:
+ * recreate a buffer from a source and the delta produced by diff-delta.c
+ *
+ * (C) 2005 Nicolas Pitre <nico@cam.org>
+ *
+ * This code is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include "delta.h"
+
+void *patch_delta(void *src_buf, unsigned long src_size,
+                 void *delta_buf, unsigned long delta_size,
+                 unsigned long *dst_size)
+{
+       const unsigned char *data, *top;
+       unsigned char *dst_buf, *out, cmd;
+       unsigned long size;
+       int i;
+
+       /* the smallest delta size possible is 6 bytes */
+       if (delta_size < 6)
+               return NULL;
+
+       data = delta_buf;
+       top = delta_buf + delta_size;
+
+       /* make sure the orig file size matches what we expect */
+       size = i = 0;
+       cmd = *data++;
+       while (cmd) {
+               if (cmd & 1)
+                       size |= *data++ << i;
+               i += 8;
+               cmd >>= 1;
+       }
+       if (size != src_size)
+               return NULL;
+
+       /* now the result size */
+       size = i = 0;
+       cmd = *data++;
+       while (cmd) {
+               if (cmd & 1)
+                       size |= *data++ << i;
+               i += 8;
+               cmd >>= 1;
+       }
+       dst_buf = malloc(size);
+       if (!dst_buf)
+               return NULL;
+
+       out = dst_buf;
+       while (data < top) {
+               cmd = *data++;
+               if (cmd & 0x80) {
+                       unsigned long cp_off = 0, cp_size = 0;
+                       const unsigned char *buf;
+                       if (cmd & 0x01) cp_off = *data++;
+                       if (cmd & 0x02) cp_off |= (*data++ << 8);
+                       if (cmd & 0x04) cp_off |= (*data++ << 16);
+                       if (cmd & 0x08) cp_off |= (*data++ << 24);
+                       if (cmd & 0x10) cp_size = *data++;
+                       if (cmd & 0x20) cp_size |= (*data++ << 8);
+                       if (cp_size == 0) cp_size = 0x10000;
+                       buf = (cmd & 0x40) ? dst_buf : src_buf;
+                       memcpy(out, buf + cp_off, cp_size);
+                       out += cp_size;
+               } else {
+                       memcpy(out, data, cmd);
+                       out += cmd;
+                       data += cmd;
+               }
+       }
+
+       /* sanity check */
+       if (data != top || out - dst_buf != size) {
+               free(dst_buf);
+               return NULL;
+       }
+
+       *dst_size = size;
+       return dst_buf;
+}