Overview

FPN module - it is a Fixed Point Number module for Redis 4, which adds decimal data type and different commands for such type.

IMPORTANT: This module works only from 4 Redis version...because modules API become available only in 4 version.

Contents

• How to load
• How to use
• Restrictions
• Development
  • Prerequisites
  • Building
• Built With
• Changelog
• Contributing
• Versioning
• Authors
• License

How to load

Just run the Redis server like this:

$> redis-server --loadmodule /<path_to_module>/fpn_module.so

You also can load the module using the following redis.conf configuration directive:

loadmodule /<path_to_module>/fpn_module.so

It is also possible to load a module at runtime using the following command:

MODULE LOAD /<path_to_module>/fpn_module.so

In order to list all loaded modules, use:

MODULE LIST

Finally, you can unload (and later reload if you wish) a module using the following command:

MODULE UNLOAD fpn_module

How to use

Available commands:

• FPN.SET key value [scale] - sets a new value for key with specified scale (optional, default is 2). It returns previous value or 0.

• FPN.GET key [scale] - gets a value by its key with specified scale (optional). If now value - it returns nil value.

• FPN.ADD key value [scale] - adds a value to the specified key, the result of the command could be converted to specific scale (optional) or it will be the max scale (ex: 12.34 + 5.678 = 18.018)

• FPN.SUBTRACT key value [scale] - subtracts a value from the specified key, the result of the command could be converted to specific scale (optional) or it will be the max scale (ex: 1.234 - 5.6 = -4.366)

• FPN.MULTIPLY key value [scale] - multiply the specified key by a value, the result of the command may be converted to specific scale (optional) or it will be the max scale

Example:

$> redis-cli FPN.GET popa.key
""
$> redis-cli FPN.SET popa.key 1.23
"0.00"
$> redis-cli FPN.ADD popa.key 3.567
"4.797"
$> redis-cli FPN.GET popa.key
"4.797"
$> redis-cli FPN.GET popa.key 2
"4.80"
$> redis-cli FPN.GET popa.key 0
"5"
$> redis-cli FPN.SUBTRACT popa.key 3
"1.797"
$> redis-cli FPN.MULTIPLY popa.key 2.36
"4.24092"
$> redis-cli FPN.MULTIPLY popa.key 2 1
"8.5"

Restrictions

The value in this lib is present as a structure:

/**
 * The structure represents decimal number.
 */
typedef struct {
  int128_t value; // 128bit integer for storing a value
  uint8_t scale;  // number of digits in mantissa
} Decimal;

int128_t has 39 digits at all (plus a sign), but we use only 38 digits, so the maximum value, which we could store in that structure, is 99_999_999_999_999_999_999_999_999_999_999_999_999 and the lowest is -99_999_999_999_999_999_999_999_999_999_999_999_999. The lib also validates your input values, like this:

$> redis-cli FPN.SET popa.key 1234567891234567890.0123456789123456789
"0.00"
$> redis-cli FPN.GET popa.key
"1234567891234567890.0123456789123456789"
$> redis-cli FPN.GET popa.key 19
"1234567891234567890.0123456789123456789"
$> redis-cli FPN.GET popa.key 20
(error) value must be greater or equal than -99_999_999_999_999_999_999_999_999_999_999_999_999 and lower or equal than 99_999_999_999_999_999_999_999_999_999_999_999_999

The error above shows us, what it couldn't conver value 1234567891234567890.0123456789123456789 to 1234567891234567890.01234567891234567890 (we have set 20 as the scale parameter), because 12_345_678_912_345_678_900_123_456_789_123_456_789 is greater than 99_999_999_999_999_999_999_999_999_999_999_999_999 (we store the whole value as integer).

Development

These instructions will get you a copy of the project up and running on your local machine for development and testing purposes.

Prerequisites

For building the project you need only a GCC.

$> git https://github.com/infobip/redis-fpn
$> cd redis-fpn

Building

The following make commands are useful:

• make build - just for building the module for your machine.

• make container_build - to build the module for Debian OS. It uses a Docker image with GCC inside it. After building, it compiles the module and puts the result into the target folder.

• make start_redis - it builds Debian module and starts a Docker container with Redis 4 and loads this module.

• make integration_tests - runs Redis with FPN module and executes integration tests against it.

IMPORTANT: The last three commands required the Docker.

Built With

• [C] - is a general-purpose, imperative computer programming language
• [make] - is a build automation tool that automatically builds executable programs and libraries from source code

Changelog

To see what has changed in recent versions of Popout, see the changelog file.

Contributing

Please read contributing file for details on my code of conduct, and the process for submitting pull requests to me.

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

Authors

• Artem Labazin - creator and the main developer

License

This project is licensed under the Apache License 2.0 License - see the license file for details