3. Exercises - Q1

Exercises from the book using checksum.py

Recommended change so -D option can use other bases:

$ diff checksum.py.ORIG checksum.py
48c48
<         values.append(int(t))
---
>         values.append(int(t,0)) # automatic base detection, 0b1010..., 0xabc, etc.
$

Q1:

$ python ./checksum.py Decimal: 216 194 107 66 Hex: 0xd8 0xc2 0x6b 0x42 Bin: 0b11011000 0b11000010 0b01101011 0b01000010 Add: ? Xor: ? Fletcher: ? --> check by hand $ python ./checksum.py -c Decimal: 216 194 107 66 Hex: 0xd8 0xc2 0x6b 0x42 Bin: 0b11011000 0b11000010 0b01101011 0b01000010 Add: 71 (0b01000111) Xor: 51 (0b00110011) Fletcher(a,b): 73,196 (0b01001001,0b11000100) Xor Add 11011000 11011000 11000010 11000010 01101011 01101011 01000010 01000010 -------- --------

$ python3 >>> d = [216, 194, 107, 66] >>> X = d[0]^d[1]^d[2]^d[3] >>> X 51 >>> bin(X) '0b110011' >>> A = d[0]+d[1]+d[2]+d[3] >>> A 583 >>> A % 256 71 >>> A & 0xff 71 >>> A % 255 73 >>> A0 = d[0]; A1 = A0+d[1]; A2 = A1+d[2]; A3 = A2+d[3] >>> (A0+A1+A2+A3) % 255 196 >>>