CS253 HW1: Serialization

Description

For this assignment, you will write a C++ program called hw1 that reads integers from standard input, translates them to a serialized format, and writes the two-digit hexadecimal form of the serialized numbers to standard output, one per line.

Definition of a vnum

We define a vnum, or variable-length number, as a two’s complement, variable number of bits (but always of the length 8n+4, where n≥0), prefixed by a four-bit length. The output will always be a whole number of bytes, or a multiple of eight bits.

You can consider the length nibble to be either:

the number of bytes-1, including the first byte
the number of additional bytes needed, after the first one.

For example, the number five, in binary, is 101₂. We need to pad that to a length of 8n+4. Since it’s three bits long, we pad it on the left to four bits: 0101₂. This requires no additional bytes, so the four-bit length is zero, or 0000₂. Put those together: 0000 0101₂, or 05₁₆.

The number three hundred, in binary, is 1 0010 1100₂. Padded to length 8n+4, that is 0001 0010 1100₂. This requires two bytes, or one additional byte, so the four-bit length is one, or 0001₂. Put those together: 0001 0001 0010 1100₂, or 112c₁₆.

The number negative one, in two’s complement binary, is 1111₂. This requires no additional bytes, so the four-bit length is zero, or 0000₂. Put those together: 0000 1111₂, or 0f₁₆.

A vnum must always be the represented using the minimum number of bytes. For example, seven must serialize as 07₁₆, not as 30 00 00 07₁₆.

A one-byte vnum (-8 ≤ n < 8)
byte #1
length				bits
0	0	0	0	b₃	b₂	b₁	b₀

A two-byte vnum
byte #1								byte #2
length				bits
0	0	0	1	b₁₁	b₁₀	b₉	b₈	b₇	b₇	b₅	b₄	b₃	b₂	b₁	b₀

A three-byte vnum
byte #1								byte #2								byte #3
length				bits
0	0	1	0	b₁₉	b₁₈	b₁₇	b₁₆	b₁₅	b₁₄	b₁₃	b₁₂	b₁₁	b₁₀	b₉	b₈	b₇	b₆	b₅	b₄	b₃	b₂	b₁	b₀

In these examples, b₀ is the least significant bit (LSB), b₁ is next most significant bit, etc.

The four-bit length field has a maximum value of 15, so this scheme can only store a 16-byte, or 124-bit number.

Sample Runs

Here are several sample runs, where % is my prompt. What you type looks like this. Your output must match exactly. Ignore the indentation.

    % make
    make output appears here
    % echo '5 300 -1 1 2 -3 40 500' | ./hw1
    5: 05
    300: 11 2c
    -1: 0f
    1: 01
    2: 02
    -3: 0d
    40: 10 28
    500: 11 f4
    % ./hw1
    -6000
    -6000: 2f e8 90
    70000
    70000: 21 11 70
    1000000000
    1000000000: 40 3b 9a ca 00
    control-D
    %

How to emit hex

// Emit two-digit hexadecimal.
int n = 200;
cout << "decimal: " << dec << n << '\n'
     << "hex: " << hex << setw(2) << setfill('0') << (n & 0xff) << '\n';

decimal: 200
hex: c8

Requirements

You may not use C-style <stdio.h> or <cstdio> facilities, such as printf, scanf, fopen, and getchar.
- Instead, use C++ facilities such as cout, and ifstream.
Read and process integers until end-of-file, or an error occurrs.
If the data is bad (for example, the word “fish” is encountered), then emit an error message to standard error and stop the program.
You may assume that, if an integer is given to the program, that it will fit into a C++ int.
Your output must look exactly like the sample runs, given that input. Spaces and leading zeroes count.
The output must end with a newline.
- Newlines do not separate lines—newlines terminate lines.
No global variables.
For readability, don’t use ASCII int constants (65) instead of char constants ('A') for printable characters.
We will compile your program as shown above.
- If that generates warnings, you will lose a point.
- If that generates errors, you will lose all points.
There is no automated testing/pre-grading/re-grading.
- Test your code yourself. It’s your job.
- Even if you only change it a little bit.
- Even if all you do is add a comment.

If you have any questions about the requirements, ask. In the real world, your programming tasks will almost always be vague and incompletely specified. Same here.

Tar file

For each assignment this semester, you will create a tar file, and turn it in.
The tar file for this assignment must be called: hw1.tar
It must contain:
- source files (*.cc)
- header files (*.h) (if any)
- Makefile (Makefile, with a capital M)
The Makefile’s default target must create the executable file hw1.
Your Makefile must use at least -Wall when compiling.
HW0 has a splendid example of a tar file.

How to submit your homework:

Use web checkin, or Linux checkin:

    ~cs253/bin/checkin HW1 hw1.tar

How to receive negative points:

Turn in someone else’s work.

CS253: Software Development with C++

Spring 2018

HW 1