More tools.

gcksum_search.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+"""
+Adds up all bytes from the beginning of a file and shows where
+a byte in the file matches the expected checksum at that location.
+"""
+
+from grmn import ChkSum
+import sys
+
+FILE = sys.argv[1]
+BLOCKSIZE = 4096
+OFFSET = 0x0
+
+csum = ChkSum()
+prev_remainder = b"\x00"
+print("Reading {} ...".format(FILE))
+with open(FILE, "rb") as f:
+    while True:
+        start_pos = f.tell()
+        block = f.read(BLOCKSIZE)
+        block = block[OFFSET:]
+        for i in range(0, len(block)):
+            c = block[i:i+1]
+            exp = bytes([csum.get_expected()])
+            if c == exp:
+                print("Found matching 0x{:02x} at 0x{:x} ({:x} + {:d}).".format(c[0], OFFSET + start_pos + i, OFFSET, start_pos + i))
+            csum.add(bytes(c))
+        if len(block) < BLOCKSIZE:
+            break
+        #break
+    f.close()