Base36_914

A fast and space-efficient Base36 encoding for large data.

About

Base36_914 encodes every 9 bytes as a block into 14 chars, with a max space efficiency of 99.5% of the theoretical limit.

If the remaining data is less than 9 bytes, the output will be padded to 14 chars. So this algorithm is suitable for longer inputs, or input length close to a multiple of 9.

Encode API

Full Block

void base36_encode_block(u8 plain[9], u8 code[14], u8 encode_table[36])

Read 9 bytes from plain and write 14 bytes to code.

The built-in BASE36_ENCODE_TABLE_DEFAULT can be used for encode_table.（0-9 a-z）

Last Block

void base36_encode_last_block(u8 plain[], int len, u8 code[14], encode_table[36])

Read len (0 < len < 9) bytes from plain and write 14 bytes to code.

All-in-One

void base36_encode(u8 plain[], int len, u8 code[], encode_table)

Read len bytes from plain and write ceil(len / 9) * 14 bytes to code.

Decode API

Full Block

void base36_decode_block(u8 code[14], u8 plain[9], u8 decode_talbe[256])

Read 14 bytes from code and write 9 bytes to plain.

The built-in BASE36_DECODE_TABLE_DEFAULT can be used for decode_talbe.

Last Block

int base36_decode_last_block(u8 code[14], u8 plain[], decode_talbe[256])

Read 14 bytes from code and write len bytes to plain.

len is the return value. (0 < len <= 9)

All-in-One

int base36_decode(u8 code[], int len, u8 plain[], decode_table)

Read len (must be a multiple of 14) bytes from code and write len / 14 * 9 bytes to plain, return len / 14 * 9.

This function calls base36_decode_last_block only once.

Stream Mode

int base36_decode_stream(u8 code[], int len, u8 plain[], decode_table)

If base36_encode is called multiple times during encoding, the 14-char-padding(s) may be located in the middle of the codes. In this case, this function must be used for decoding.

This function always uses base36_decode_last_block, and returns the length of the decoded data.

Check

None of the above decoding functions check the input code, it needs to be checked by the caller.

Even if the input code is out of the code table, the decoding functions can still work, just with wrong result. If the decoded data has an integrity check, the input check can be ignored.

Demo1

demo-wasm

Online: https://etherdream.com/base36/

Demo2

demo-pipe

Test:

./base36 <<< "Hello World 12345"

Print gatk40t14s0idcgzbz9l6nvgmq31.

Encode:

./base36 < file > file36.txt

Decode:

./base36 -d < file36.txt > file-re

TODO

SIMD support.