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Original file line number Diff line number Diff line change
Expand Up @@ -2,10 +2,10 @@

Implement variable length quantity encoding and decoding.

The goal of this exercise is to implement [VLQ](https://en.wikipedia.org/wiki/Variable-length_quantity) encoding/decoding.
The goal of this exercise is to implement [VLQ][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).
Only the first 7 bits of each byte are 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.
Expand All @@ -30,3 +30,5 @@ Here are examples of integers as 32-bit values, and the variable length quantiti
08000000 C0 80 80 00
0FFFFFFF FF FF FF 7F
```

[vlq]: https://en.wikipedia.org/wiki/Variable-length_quantity
Original file line number Diff line number Diff line change
@@ -0,0 +1,33 @@
use variable_length_quantity as vlq;
{% for test in cases %}
#[test]
{% if loop.index != 1 -%}
#[ignore]
{% endif -%}
fn {{ test.description | slugify | replace(from="-", to="_") }}() {
{%- if test.property == "encode" %}
let input = &{{ test.input.integers | json_encode() }};
let output = vlq::{{ fn_names[0] }}(input);
let expected = vec![
{%- for byte in test.expected -%}
0x{{ byte | to_hex }},
{%- endfor -%}
];
{%- elif test.property == "decode" %}
let input = &[
{%- for byte in test.input.integers -%}
0x{{ byte | to_hex }},
{%- endfor -%}
];
let output = vlq::{{ fn_names[1] }}(input);
let expected = {% if test.expected is object -%}
Err(vlq::Error::IncompleteNumber)
{%- else -%}
Ok(vec!{{ test.expected | json_encode() }})
{%- endif %};
{%- else %}
panic!("unknown property: {{ test.property }}");
{%- endif %}
assert_eq!(output, expected);
}
{% endfor -%}
91 changes: 88 additions & 3 deletions exercises/practice/variable-length-quantity/.meta/tests.toml
Original file line number Diff line number Diff line change
@@ -1,3 +1,88 @@
# This is an auto-generated file. Regular comments will be removed when this
# file is regenerated. Regenerating will not touch any manually added keys,
# so comments can be added in a "comment" key.
# This is an auto-generated file.
#
# Regenerating this file via `configlet sync` will:
# - Recreate every `description` key/value pair
# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
# - Preserve any other key/value pair
#
# As user-added comments (using the # character) will be removed when this file
# is regenerated, comments can be added via a `comment` key.

[35c9db2e-f781-4c52-b73b-8e76427defd0]
description = "Encode a series of integers, producing a series of bytes. -> zero"

[be44d299-a151-4604-a10e-d4b867f41540]
description = "Encode a series of integers, producing a series of bytes. -> arbitrary single byte"

[ea399615-d274-4af6-bbef-a1c23c9e1346]
description = "Encode a series of integers, producing a series of bytes. -> largest single byte"

[77b07086-bd3f-4882-8476-8dcafee79b1c]
description = "Encode a series of integers, producing a series of bytes. -> smallest double byte"

[63955a49-2690-4e22-a556-0040648d6b2d]
description = "Encode a series of integers, producing a series of bytes. -> arbitrary double byte"

[29da7031-0067-43d3-83a7-4f14b29ed97a]
description = "Encode a series of integers, producing a series of bytes. -> largest double byte"

[3345d2e3-79a9-4999-869e-d4856e3a8e01]
description = "Encode a series of integers, producing a series of bytes. -> smallest triple byte"

[5df0bc2d-2a57-4300-a653-a75ee4bd0bee]
description = "Encode a series of integers, producing a series of bytes. -> arbitrary triple byte"

[f51d8539-312d-4db1-945c-250222c6aa22]
description = "Encode a series of integers, producing a series of bytes. -> largest triple byte"

[da78228b-544f-47b7-8bfe-d16b35bbe570]
description = "Encode a series of integers, producing a series of bytes. -> smallest quadruple byte"

[11ed3469-a933-46f1-996f-2231e05d7bb6]
description = "Encode a series of integers, producing a series of bytes. -> arbitrary quadruple byte"

[d5f3f3c3-e0f1-4e7f-aad0-18a44f223d1c]
description = "Encode a series of integers, producing a series of bytes. -> largest quadruple byte"

[91a18b33-24e7-4bfb-bbca-eca78ff4fc47]
description = "Encode a series of integers, producing a series of bytes. -> smallest quintuple byte"

[5f34ff12-2952-4669-95fe-2d11b693d331]
description = "Encode a series of integers, producing a series of bytes. -> arbitrary quintuple byte"

[7489694b-88c3-4078-9864-6fe802411009]
description = "Encode a series of integers, producing a series of bytes. -> maximum 32-bit integer input"

[f9b91821-cada-4a73-9421-3c81d6ff3661]
description = "Encode a series of integers, producing a series of bytes. -> two single-byte values"

[68694449-25d2-4974-ba75-fa7bb36db212]
description = "Encode a series of integers, producing a series of bytes. -> two multi-byte values"

[51a06b5c-de1b-4487-9a50-9db1b8930d85]
description = "Encode a series of integers, producing a series of bytes. -> many multi-byte values"

[baa73993-4514-4915-bac0-f7f585e0e59a]
description = "Decode a series of bytes, producing a series of integers. -> one byte"

[72e94369-29f9-46f2-8c95-6c5b7a595aee]
description = "Decode a series of bytes, producing a series of integers. -> two bytes"

[df5a44c4-56f7-464e-a997-1db5f63ce691]
description = "Decode a series of bytes, producing a series of integers. -> three bytes"

[1bb58684-f2dc-450a-8406-1f3452aa1947]
description = "Decode a series of bytes, producing a series of integers. -> four bytes"

[cecd5233-49f1-4dd1-a41a-9840a40f09cd]
description = "Decode a series of bytes, producing a series of integers. -> maximum 32-bit integer"

[e7d74ba3-8b8e-4bcb-858d-d08302e15695]
description = "Decode a series of bytes, producing a series of integers. -> incomplete sequence causes error"

[aa378291-9043-4724-bc53-aca1b4a3fcb6]
description = "Decode a series of bytes, producing a series of integers. -> incomplete sequence causes error, even if value is zero"

[a91e6f5a-c64a-48e3-8a75-ce1a81e0ebee]
description = "Decode a series of bytes, producing a series of integers. -> multiple values"
1 change: 0 additions & 1 deletion exercises/practice/variable-length-quantity/src/lib.rs
Original file line number Diff line number Diff line change
@@ -1,7 +1,6 @@
#[derive(Debug, PartialEq, Eq)]
pub enum Error {
IncompleteNumber,
Overflow,
}

/// Convert a list of numbers to a stream of bytes encoded with variable length encoding.
Expand Down
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