From 6da125adbed4c279a899f91a699c648a06fbae5f Mon Sep 17 00:00:00 2001
From: Markus Birth <mbirth@gmail.com>
Date: Sun, 14 Oct 2018 22:45:16 +0200
Subject: [PATCH] More output after checksum calc.

---
 gcksum.py | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/gcksum.py b/gcksum.py
index b8c2528..1023e36 100644
--- a/gcksum.py
+++ b/gcksum.py
@@ -9,16 +9,23 @@ FILE = sys.argv[1]
 
 print("Opening {}".format(FILE))
 
+csum_pre = 0
 csum = 0
 
 with open(FILE, "rb") as f:
     while True:
         block = f.read(1024)
         for c in block:
+            csum_pre = csum
             csum += c
             csum &= 0xff
         if len(block) < 1024:
             print("End reached.")
             break
 
-print("Sum of all bytes: {}".format(csum))
+print("Sum of all bytes: {:02x}".format(csum))
+print("Sum without last: {:02x}".format(csum_pre))
+
+expected_cksum = ( 0x100 - csum_pre ) & 0xff
+
+print("Expected last byte: {:02x}".format(expected_cksum))