added rpssl snippet

Assignment3/rpssl.py

@@ -0,0 +1,123 @@
+# coding: utf-8
+import os, sys, subprocess
+import time
+from z3 import *
+
+CHOICES = ["Rock", "Paper", "Scissors", "Spock", "Lizard"]
+
+def next_random_number(s_i):
+    return ((11 * s_i) + 12345) & 0x7fff
+
+class RPSSLComputer:
+    def __init__(self, s0):
+        self.previous_random_number = s0
+
+    def compute_choice(self):
+        random_number = next_random_number(self.previous_random_number)
+        self.previous_random_number = random_number
+        return random_number % 5, CHOICES[random_number % 5]
+
+
+# cf. https://bigbangtheory.fandom.com/wiki/Rock,_Paper,_Scissors,_Lizard,_Spock
+def winning_mapping(i):
+    if i == 0: return 1#"Paper"
+    if i == 1: return 2#"Scissors"
+    if i == 2: return 0#"Rock"
+    if i == 3: return 4#"Lizard"
+    if i == 4: return 0#"Rock"
+    return "Did you forget to compute the remainder modulo 5?"
+
+def compute_winner(computer, player):
+    if computer == player:
+        return "\tTie.", False
+    is_player_bigger = True if player > computer else False
+    absolute_difference = abs(computer - player)
+    if absolute_difference % 2 == 1:
+        if is_player_bigger:
+            return "\tPlayer wins.", True
+        else:
+            return "\tComputer wins.", False
+    else:
+        if is_player_bigger:
+            return "\tComputer wins.", False
+        else:
+            return "\tPlayer wins.", True
+
+solver = Solver()
+states = list()
+
+# We are adding the first state s_0 to the list of states
+states.append(BitVec("state0", 16))
+
+s0 = int(sys.argv[1])
+computer = RPSSLComputer(s0)
+
+preprocess_count = 5
+
+def add_constraint(solver, index, computers_choice):
+    # TODO create a BitVec and append it to the list of states
+    # You might want to call it state{index}
+
+    # TODO Enforce that the newly added BitVec-variable must evaluate to the result of the LCG computation using the previous result
+
+    # TODO Enforce that the unsigned remainder of the newly added BitVec-varialbe and 5 evaluates to the choice of the computer
+
+    pass
+
+def store_backtracking_point(solver):
+    solver.push()
+
+def restore_backtracking_point(solver):
+    solver.pop()
+
+def add_next_state_constraint(solver):
+    s_i_plus_1 = BitVec("s_i_plus_1", 16)
+    # TODO Enforce that the next state value is computed via the same computation as above
+
+    return s_i_plus_1
+
+def get_players_choice(solver, s_i_plus_1):
+    # TODO Get the value of next_state from the model and return it modulo 5
+    # Hint: winning_mapping(...) returns a good answer for the computer's choice
+    # Hint: use solver.model() like a python dict.
+    # Hint: use `.as_long()` to convert a z3 variable to a python integer value
+    return 0
+
+
+# Main loop:
+
+# We read preprocess_count many choices from the computer before we start to ask z3 for a solution
+# Note that for these preprocessing rounds we do not need to make a good guess and compute the winner
+# We are only interested in what the computer picks for the first few rounds
+for index in range(1,preprocess_count):
+    computer_choice, _ = computer.compute_choice()
+    player_choice = 0 # We always choose Rock since we cannot make good guesses in the beginning
+
+    add_constraint(solver,index,computer_choice)
+    output, won = compute_winner(computer_choice, player_choice)
+    print(output)
+    if won: print("Congratulations!")
+    else:   print("Try again.")
+
+
+# Now we start by adding a 'special' variable s_i_plus_1 and try to win
+index = preprocess_count
+while True:
+    store_backtracking_point(solver)
+    s_i_plus_1 = add_next_state_constraint(solver)
+    solver.check()
+
+    player_choice = get_players_choice(solver, s_i_plus_1)
+    computer_choice, _ = computer.compute_choice()
+    output, won = compute_winner(computer_choice, player_choice)
+
+    print(output)
+    if won: print("Congratulations!")
+    else:   print("Try again.")
+
+    restore_backtracking_point(solver)
+    add_constraint(solver, index, computer_choice)
+    # input("")
+    index += 1
+    if index >= 100:
+        break