Problem Set 8 An inventory of blockchains


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CPSC 427: Object-Oriented Programming Handout #10

Problem Set 8

1 Introduction
This 10-point assignment is required for graduate students and anyone else registered under
CPSC 527. It is optional for students registered under CPSC 427. For those students,
points earned on this assignment will offset points lost on previous homework assignments,
but they will not apply against points lost on exams, nor will they permit anyone to earn
more than 100% of the possible homework points.
The due date for this assignment is the same as that for homework assignment 7. However, they are separate assignments and should be submitted separately.
2 Problem
The goal of this assignment is to modify your solution to homework assignment 7 to gather
and print additional information about the progress of the simulation.
An inventory of blockchains is a pr´ecis of the current set of choices of all of the agents
in the population. A sample inventory from a real simulation run with 10 agents is:
Inventory: 5 active blockchain(s):
1 copies of [0,1] [1,46] [2,123] [3,255]
1 copies of [0,1] [1,46] [2,123] [3,271]
6 copies of [0,1] [1,46] [2,123]
1 copies of [0,1] [1,46] [2,160]
1 copies of [0,1] [1,46] [2,236]
We see that all of the agents agree on the level-0 and level-1 blocks of each chain and
eight agents agree on level-2 block [2,123]. However, two different chains have already
been forked from it, so two agents have distinct level-3 blocks, and it is unclear which will
eventually win out.
Thus, an inventory is a compressed version of the current choices of the population
that allows one to relatively quickly find those blocks for which consensus has already been
achieved. However, finding consensus blocks is not a part of this assignment. All that is
required is to create the initial inventory, to maintain it step by step during the simulation,
and to print it when required (in the format shown above).
3 Programming Notes
1. You should create a class Inventory whose sole data member is a std::map.
2 Problem Set 8
2. To maintain the inventory, you should write functions add() and sub that add (insert) and subtract (remove) blockchains from the inventory, respectively. After each
simulation step, if the agent’s new and old choices differ, the new one should be added
and the old one subtracted from the inventory.
3. There should be no occurrences of new in PS8 other than those already present in
PS7. In particular, the map should be composed in Inventory and not be a dynamic
extension. Keeping the use of dynamic storage confined to classes that can manage it
such as SPtr and std::map simplies your code and makes it less likely to have hidden
errors. Remember the motto: “No new’s is good news!”
4. You should define Blockchain::operator<() and Blockchain::operator==(). The
default definitions won’t work properly because they end up comparing the embedded
SPtr’s, which will always differ in their my_id fields, even when one is a copy of
another. For our purposes, it works to compare the serial numbers of the last block
in the chain to which each Blockchain points.
5. The same sample call on your simulator that was provided for PS7 is given again on the
Zoo in /c/cs427/code/ps8/, along with the corresponding output. Note
that adding the inventory to your PS7 code will change the serial numbers assigned
to the blocks. This is okay.
4 Grading Rubric
Your assignment will be graded according to the scale given in Figure 1 (see below).
# Pts. Item
1. 1 All relevant standards from previous problem sets are followed regarding submission, identification of authorship on all files, and so forth. A
well-formed Makefile or makefile is submitted that specifies compiler
options -O1 -g -Wall -std=c++17. Running make successfully compiles
and links the project and results in an executable file blockchain. Each
function definition is preceded by a comment that describes clearly what
it does.
2. 1 Sample input and output files are submitted that show good coverage of
the parameter space, e.g., small inputs, large inputs, edge cases for the
probabilities (e.g., 0.0 and 1.0) as well as reasonable intermediate cases.
This is in addition to the furnished sample file.
3. 1 The program shows good style. All functions are clean and concise. Inline
initializations, inline functions, and const are used where appropriate.
Variable names are appropriate to the context. Programs are consistently
indented according to the course indenting style. Each class has a separate
.hpp file and, if needed, a separate .cpp file.
4. 2 The guidelines in section 3 are followed.
5. 5 All of the functionality in section 2 is correctly implemented.
10 Total points.
Figure 1: Grading rubric.

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