cls / b64fix

Compute the Base64 fixpoint up to a given precision

Base64 Fixpoint

A few days ago I saw someone by the name of p4bl0 mention that the Base64 encoding has a fixpoint. That is, if you repeatedly Base64-encode any string, the result will tend towards the same unique (infinite) string of characters.

This caught my interest. I wrote this C++ program to compute that fixpoint up to a specified precision (in sextets). It does this by, instead of repeatedly Base64-encoding a string, simply keeping track of the delta between the 8-bit input and 6-bit output (prior to table lookup).

The result is reasonably fast:

cls@chalk$ n=$((32*1024*1024)) # 32 MiB
cls@chalk$ time ./b64fix $n > b64fix.txt
real    0m0.888s
user    0m0.772s
sys     0m0.099s
cls@chalk$ cmp -n $((n*4/3)) b64fix.txt <(base64 -w 0 b64fix.txt)
cls@chalk$

For more information, see https://news.ycombinator.com/item?id=37987225