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https://github.com/colored-coins/sffc
sffc-encoder provides the encode/decode functions to and from SFFC (Significant Figures First Code) format.
https://github.com/colored-coins/sffc
Last synced: 2 months ago
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sffc-encoder provides the encode/decode functions to and from SFFC (Significant Figures First Code) format.
- Host: GitHub
- URL: https://github.com/colored-coins/sffc
- Owner: Colored-Coins
- Created: 2015-06-04T22:37:00.000Z (over 9 years ago)
- Default Branch: master
- Last Pushed: 2017-10-08T19:45:57.000Z (over 7 years ago)
- Last Synced: 2024-04-24T14:37:20.956Z (10 months ago)
- Language: JavaScript
- Homepage:
- Size: 13.7 KB
- Stars: 0
- Watchers: 6
- Forks: 6
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# sffc-encoder
[](https://travis-ci.org/Colored-Coins/SFFC) [](https://coveralls.io/r/Colored-Coins/SFFC?branch=master) [](http://badge.fury.io/js/sffc-encoder) [](http://slack.coloredcoins.org)
[](https://github.com/feross/standard)
sffc-encoder provides the encode/decode functions to and from SFFC (Significant Figures First Code) format.
SFFC format is an Integer to binary encoding format with a changing byte size (full bytes) based on the number of significant digits in base 10 that are needed to represent the Integer.
This format benefits the more "rounded" (Higher powers of 10) Integer with a lower byte size encoding.
The decoding Scheme:
- First 2 or 3 bits are length flag:
1. If first 2 bits are 1 then the flag is 2 bits.
2. Else the flag is the first 3 bits.
- Remove the flag bits and concat the rest with the next extra amount of bytes using the conversion table (appendix A).
- Split the bits to mantis and exponent to their respective bits using table 1.
- Multiply the mantis by 10^exponent in base 10 to get the encoded Integer.
There is also some encoding optimization, for example, even though 23 has 2 significant figures we can still encode it using 3 flag bits and 5 binary bits in only 1 byte.
### Installation
```sh
$ npm install sffc-encoder
```
### Encode
Params:
- number - takes any integer between 0 to 9007199254740991 (`Number.MAX_SAFE_INTEGER`)
Returns a new Buffer holding the encoded Integer
```js
var sffc = require('sffc-encoder')
console.log(sffc.encode(1321321321)) // Will print:
console.log(sffc.encode(1)) // Will print:
```
### Decode
Params:
- consume - takes a consumable buffer (You can use [buffer-consumer] like in the example to create one)
Returns the Integer as number
```js
var sffc = require('sffc-encoder')
var consumer = require('buffer-consumer')
var codeBuffer = new Buffer([0x82,0x76,0x0e,0x1b,0x48])
console.log(sffc.decode(consumer(codeBuffer))) // Will print: 1321321321
```
### Testing
In order to test you need to install [mocha] globaly on your machine
```sh
$ cd /"module-path"/sffc-encoder
$ mocha
```
### Apendix A
-------------------------------------------------------------------------------------------------------------------------
|Byte Flag | Significant Digits | Mantis bit size | Exponent bit size | Extra Bytes | Total Bytes|
|----------|---------------------------------------------|-----------------|-------------------|-------------|------------|
|000 | 1-31 (Number Value, not significant digits) | 5 | 0 | 0 | 1 |
|001 | 2 | 9 | 4 | 1 | 2 |
|010 | 5 | 17 | 4 | 2 | 3 |
|011 | 7 | 25 | 4 | 3 | 4 |
|100 | 10 | 34 | 3 | 4 | 5 |
|101 | 12 | 42 | 3 | 5 | 6 |
|11* | 16 | 54 | 0 | 6 | 7 |
-------------------------------------------------------------------------------------------------------------------------
License
----
[Apache-2.0](http://www.apache.org/licenses/LICENSE-2.0)
[mocha]:https://www.npmjs.com/package/mocha
[buffer-consumer]:https://www.npmjs.com/package/buffer-consumer