variable-length-quantity

Variable Length Quantity

Implement variable length quantity encoding and decoding.

The goal of this exercise is to implement VLQ encoding/decoding.

In short, the goal of this encoding is to encode integer values in a way that would save bytes. Only the first 7 bits of each byte is significant (right-justified; sort of like an ASCII byte). So, if you have a 32-bit value, you have to unpack it into a series of 7-bit bytes. Of course, you will have a variable number of bytes depending upon your integer. To indicate which is the last byte of the series, you leave bit #7 clear. In all of the preceding bytes, you set bit #7.

So, if an integer is between 0-127, it can be represented as one byte. Although VLQ can deal with numbers of arbitrary sizes, for this exercise we will restrict ourselves to only numbers that fit in a 32-bit unsigned integer. Here are examples of integers as 32-bit values, and the variable length quantities that they translate to:

 NUMBER        VARIABLE QUANTITY
00000000              00
00000040              40
0000007F              7F
00000080             81 00
00002000             C0 00
00003FFF             FF 7F
00004000           81 80 00
00100000           C0 80 00
001FFFFF           FF FF 7F
00200000          81 80 80 00
08000000          C0 80 80 00
0FFFFFFF          FF FF FF 7F

Rust Installation

Refer to the exercism help page for Rust installation and learning resources.

Writing the Code

Execute the tests with:

$ cargo test

All but the first test have been ignored. After you get the first test to pass, open the tests source file which is located in the tests directory and remove the #[ignore] flag from the next test and get the tests to pass again. Each separate test is a function with #[test] flag above it. Continue, until you pass every test.

If you wish to run all ignored tests without editing the tests source file, use:

$ cargo test -- --ignored

To run a specific test, for example some_test, you can use:

$ cargo test some_test

If the specific test is ignored use:

$ cargo test some_test -- --ignored

To learn more about Rust tests refer to the online test documentation

Make sure to read the Modules chapter if you haven't already, it will help you with organizing your files.

Further improvements

After you have solved the exercise, please consider using the additional utilities, described in the installation guide, to further refine your final solution.

To format your solution, inside the solution directory use

cargo fmt

To see, if your solution contains some common ineffective use cases, inside the solution directory use

cargo clippy --all-targets

Submitting the solution

Generally you should submit all files in which you implemented your solution (src/lib.rs in most cases). If you are using any external crates, please consider submitting the Cargo.toml file. This will make the review process faster and clearer.

Feedback, Issues, Pull Requests

The exercism/rust repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!

If you want to know more about Exercism, take a look at the contribution guide.

Source

A poor Splice developer having to implement MIDI encoding/decoding. https://splice.com

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.